2nd Edition
C. J. Baker, K. E. Saxton,W. R. Ritchie,W. C. T. Chamen,
D. C. Reicosky, F. Ribeiro, S. E. Justice and P. R. Hobbs
No-tillage Seeding in
Conservation Agriculture
No-tillage Seeding in Conservation Agriculture
Second Edition
This book is dedicated to the scientists and students whose work is reviewed, together with
their long-suffering families. Such people were driven by a desire to make no-tillage as sustainable
and risk-free as possible, and in the process to make food production itself sustainable
for the first time in history. The odds were great but the results have been significant
and will have far-reaching consequences.
No-tillage Seeding in Conservation
Agriculture
Second Edition
C.J. Baker, K.E. Saxton, W.R. Ritchie, W.C.T. Chamen,
D.C. Reicosky, M.F.S. Ribeiro, S.E. Justice and P.R. Hobbs
Edited by
C.J. Baker and K.E. Saxton
Published by
Food and Agriculture Organization of the United Nations
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Library of Congress Cataloging-in-Publication Data
No-tillage seeding in conservation agriculture/C.J. Baker . . . [et al.] edited by
C.J. Baker and K.E. Saxton.-- 2nd ed.
p. cm.
Rev. ed. of: No-tillage seeding/C.J. Baker. 1996.
Includes bibliographical references and index.
ISBN 1-84593-116-5 (alk. paper)
1. No-tillage. I. Baker, C.J. (C. John) II. Saxton, Keith E., 1937- III. Baker, C.J.
(C. John). No-tillage seeding. IV. Food and Agriculture Organization of the
United Nations. V. Title.
S604.B36 2006
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2005035401
Published jointly by CAB International and FAO.
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ISBN-10: 1-84593-116-5 (CABI)
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ISBN: 92-5-105389-8 (FAO)
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Contents
Contributors xi
Foreword to the Second Edition xii
Shivaji Pandey and Theodor Friedrich
Preface xiii
1 The ‘What’ and ‘Why’ of No-tillage Farming 1
C. John Baker and Keith E. Saxton
What is No-tillage? 3
Why No-tillage? 5
Advantages 6
Disadvantages 7
Summary of the 'What' and 'Why' of No-tillage 10
2 The Benefits of No-tillage 11
Don C. Reicosky and Keith E. Saxton
Introduction 11
Principles of Conservation Agriculture 12
Crop Production Benefits 13
Increased organic matter 14
Increased available soil water 15
Reduced soil erosion 15
Enhanced soil quality 16
Improved nutrient cycles 17
Reduced energy requirements 17
Carbon Emissions and Sequestration 19
Summary of the Benefits of No-tillage 20
v
3 The Nature of Risk in No-tillage 21
C. John Baker, W. (Bill) R. Ritchie and Keith E. Saxton
What is the Nature of Risk in No-tillage? 21
Biological risks 21
Physical risks 24
Chemical risks 27
Economic risk 29
Conclusions 32
Summary of the Nature of Risk in No-tillage 33
4 Seeding Openers and Slot Shape 34
C. John Baker
Vertical Slots 35
V-shaped slots 35
Slanted V-shaped slots 40
U-shaped slots 40
Vibrating openers 50
Horizontal Slots 51
Inverted T-shaped slots 51
Punch Planting 56
Surface Broadcasting 57
Summary of Seeding Openers and Slot Shape 58
5 The Role of Slot Cover 60
C. John Baker
The Role of Soil Humidity 63
Methods of Covering Seed Slots 65
Squeezing 67
Rolling 67
Pressing 68
Scuffing 69
Deflecting 69
Tilling 71
Folding 71
Summary of the Role of Slot Cover 72
6 Drilling into Dry Soils 74
C. John Baker
How Soils Lose Moisture 74
The Role of Vapour-phase Soil Water 75
Germination 76
Subsurface Survival 77
Seedling Emergence 80
The Effects of Pressing 83
Field Experience 84
Summary of Drilling into Dry Soils 84
vi Contents
7 Drilling into Wet Soils 85
C. John Baker
Drilling Wet Soils 85
Vertical double (or triple) disc openers (V-shaped slots) 86
Slanted double (or triple) disc openers (slanted V-shaped slots) 86
Vertical angled flat (or dished) disc openers (U-shaped slots) 86
Hoe-type openers (U-shaped slots) 86
Power till openers (U-shaped slots) 87
Winged openers (inverted-T-shaped slots) 87
Drilled Dry Soils that Become Wet 89
Opener performance 93
Summary of Drilling into Wet Soils 98
8 Seed Depth, Placement and Metering 99
C. John Baker and Keith E. Saxton
Seeding Depth and Seedling Emergence 100
Maintaining Consistent Opener Depth 101
Surface following 101
Depth-gauging devices 101
The value of semi-pneumatic tyres 103
Walking beams 104
Disc seed flick 105
Soil disturbance 105
Residue hairpinning or tucking 105
Opener bounce 105
Seed bounce 106
Slot closure 106
Drill and Planter Functions 106
Downforce mechanisms 106
Seed metering and delivery 113
Summary of Seed Depth, Placement and Metering 116
9 Fertilizer Placement 118
C. John Baker
Toxicity 119
Banded fertilizer 120
Vertical banding versus horizontal banding 121
Retention of gaseous fertilizers 126
Crop Yield 126
Banding options 128
How close should banded fertilizer be to the seed? 131
Conclusion 132
Summary of Fertilizer Placement 133
10 Residue Handling 134
C. John Baker, Fatima Ribeiro and Keith E. Saxton
The Forms that Residues can Take 134
Short root-anchored standing vegetation 134
Tall root-anchored standing vegetation 136
Lying straw or stover 136
Contents vii
Management of Residues on a Field Scale 138
Large field-scale no-tillage 138
Small-scale no-tillage 140
Management of Residues by Openers, Drills and Planters: Micro-management of
Crop Residues 145
Opener handling of residues 145
Row cleaners 147
Chopping of straw into short lengths 147
Random cutting of straw in place 149
Wet versus dry straw 155
The case for and against scrapers 156
Clearance between openers 156
Summary of Residue Handling 158
11 Comparing Surface Disturbance and Low-disturbance Disc Openers 159
C. John Baker
Minimum versus Maximum Slot Disturbance – How Much
Disturbance is Too Much? 159
Disturbance effects 160
Disc opener feature comparisons 163
Summary of Comparing Surface Disturbance and
Low-disturbance Disc Openers 163
12 No-tillage for Forage Production 168
C. John Baker and W. (Bill) R. Ritchie
Forage Species 168
Integrated Systems 169
No-tillage of Pasture Species 171
Pasture renewal 171
Pasture renovation 175
Seed metering 183
Summary of No-tillage for Forage Production 183
13 No-tillage Drill and Planter Design – Large-scale Machines 185
C. John Baker
Operating Width 185
Surface Smoothing 186
Power Requirements 189
Weight and Opener Forces 190
Re-establishing Downforce 194
Wheel and Towing Configurations 195
End wheels 196
Fore-and-aft wheels 196
Matching Tractors to Drills and Planters 198
Product Storage and Metering 200
Summary of No-tillage Drill and Planter Design – Large-scale Machines 202
viii Contents
14 No-tillage Drill and Planter Design – Small-scale Machines 204
Fatima Ribeiro, Scott E. Justice, Peter R. Hobbs and C. John Baker
Characteristics 204
Range of Equipment 204
Hand-jab planters (dibblers) 205
Row-type planters (animal-drawn and tractor-mounted) 206
Animal-drawn planters 212
Planters adapted from power tillers 212
Tractor-drawn planters 213
No-tillage farming in Asia 213
Summary of No-tillage Drill and Planter Design – Small-scale Machines 225
15 Managing a No-tillage Seeding System 226
W. (Bill) R. Ritchie and C. John Baker
Site Selection and Preparation 226
Weed Competition 227
Pest and Disease Control 228
Managing Soil Fertility 228
Seeding Rates and Seed Quality 228
Operator Skills 229
Post-seeding Management 230
Planning – the Ultimate Management Tool 230
Cost Comparisons 234
Summary of Managing a No-tillage Seeding System 235
16 Controlled-traffic Farming as a Complementary Practice to No-tillage 236
W.C. Tim Chamen
What is Controlled-traffic Farming? 236
Why Adopt a CTF Regime within a No-tillage Farming System? 236
The benefits of CTF 236
The effects of CTF on soil conditions 237
Making CTF Happen 245
Basic principles 245
Forward planning and machinery matching 245
The width-matching process 245
Field layout and system management 248
Orientation of permanent wheel ways 249
Wheel-way management 249
Guidance systems 251
Economics 251
Transition costs and timescale for change to CTF 252
Fixed and variable costs 253
Change in output 253
In-field management costs 254
Summary of costs and returns 254
Summary of Controlled-traffic Farming as a Complementary
Practice to No-tillage 254
Contents ix
17 Reduced Environmental Emissions and Carbon Sequestration 257
Don C. Reicosky and Keith E. Saxton
Introduction 257
Tillage-induced Carbon Dioxide Emissions 257
Emission measurements 258
Tillage and residue effects 258
Strip tillage and no-tillage effects on CO2 loss 260
Carbon Sequestration Using No-tillage 262
Nitrogen Emissions 263
Policy of Carbon Credits 265
Summary of Reduced Environmental Emissions and
Carbon Sequestration 267
18 Some Economic Comparisons 268
C. John Baker
New Zealand Comparisons 269
Assumptions 269
General conclusions 274
European Comparisons 275
Summary of Some Economic Comparisons 276
19 Procedures for Development and Technology Transfer 277
C. John Baker
Plant Responses to No-tillage Openers in Controlled Conditions 278
The micro-environment within and surrounding no-tillage seed slots 281
Soil Compaction and Disturbance by No-tillage Openers 284
Soil strength 284
Instantaneous soil pressure (stress) 286
Instantaneous and permanent soil displacement 287
Soil bulk density 287
Smearing and compaction 287
Locating Seeds in the Soil 287
Seed spacing 287
Seed depth 287
Lateral positioning of seeds relative to the centre line of the slot 288
Seed Travel within No-tillage Openers 289
Drag on a Disc Opener 291
Accelerated Wear Tests of No-tillage Openers 292
Effects of Fertilizer Banding in the Slot 292
Prototype Drills and Management Strategies 294
Single-row test drills 294
Simultaneous field testing of several opener designs 295
Plot-sized field drills and planters 297
Field-scale prototype drills and a drilling service for farmers 297
Summary of Drill Development and Technology Transfer 299
References 301
Index 317
x Contents
Contributors
C.J. Baker, Centre for International No-tillage Research and Engineering (CINTRE),
Feilding, New Zealand
W.C.T. Chamen, 4Ceasons Agriculture and Environment, Maulden, Bedfordshire, UK
P.R. Hobbs, Department of Crops and Soil Science, Cornell University, Ithaca, New York,
USA
S.E. Justice, National Agriculture and Environment Forum (NAEF), Kathmandu, Nepal
D.C. Reicosky, United States Department of Agriculture, Agricultural Research Service,
Morris, Minnesota, USA
M.F.S. Ribeiro, Instituto Agronômico do Paraná (IAPAR), Ponta Grossa, Parana, Brazil
W.R. Ritchie, Centre for International No-tillage Research and Engineering (CINTRE),
Feilding, New Zealand
K.E. Saxton, Retired, formerly United States Department of Agriculture, Agricultural
Research Service, Pullman, Washington, USA
xi
xii
Foreword to the Second Edition
The Food and Agriculture Organization (FAO) has a history of supporting the development
and extension of conservation agriculture cropping systems. No-tillage seeding is one of
the key operations of conservation agriculture; no-till seeding, together with the principles
of cover crops and crop rotation, constitute conservation agriculture. The availability of
suitable technology and equipment is a necessary precondition for making conservation
agriculture work. Special equipment is required not only for direct seeding and planting,
but also for the management of crop residues and cover crops.
The earlier book, entitled No-tillage Seeding: Science and Practice, by Baker, Saxton
and Ritchie, was, at the time of its publication, one of the most comprehensive publications
covering the engineering aspects of no-tillage seeding as well as the agronomic and environmental
background for no-tillage farming. It has been valuable as a reference for scientists
and students, and also as a guide for practitioners. A case was reported where a farmer
after reading this book bought a no-till planter and converted his farm to no-till.
This new book, No-tillage Seeding in Conservation Agriculture, provides a broader picture
of the equipment used in conservation agriculture cropping systems. It includes chapters on
material not previously covered, for example, the management of crop residues and cover
crops, preparation for the no-tillage seeding operation, and controlled-traffic farming as a complementary
technology. There are also new chapters describing no-tillage seeding technologies
for small-scale farmers. Technology developments from South America and South Asia are
described, including manual equipment, draught-animal equipment and equipment for power
tillers. The subject of greenhouse gases as driving forces for climate change is also discussed in
a chapter on carbon sequestration under no-tillage farming systems.
We hope that this book contributes to a better understanding of the engineering components
of conservation agriculture. It is also our wish that it helps with the introduction and
expanded application of this technology. Conservation agriculture is a valuable approach to
cropping that can lead to more productive, competitive and sustainable agricultural systems
with parallel benefits to the environment and to farmers and their families.
Shivaji Pandey
Director
Theodor Friedrich
Senior Agricultural Engineer
Agricultural Support Systems Division
FAO
Rome, November 2005
Preface
And he gave for his opinion, that whoever could make two ears of corn or
two blades of grass to grow upon a spot of ground where only one grew before,
would deserve better of mankind, and do more essential service to
his country than the whole race of politicians put together.
Jonathan Swift, Gulliver’s Travels (1726)
‘A Voyage to Brobdingnag’
The authors of this book describe and analyse no-tillage technologies, particularly those
related to no-tillage seed drilling, from a variety of accumulated experiences over the past
40 years. Most of us set out to discover why no-tillage did not always work and how to
overcome these obstacles. The more we learned the more appealing no-tillage farming
became. The understanding and system science have now been acquired and tested to the
point where we are ever more confident it represents the future of farming.
Some of the reported research started from knowledge that none of the traditional
drills, planters or opener technologies used for tillage farming then provided a fail-safe
methodology for untilled, residue-covered soils. Inevitably that resulted in new machine
designs and evaluations, and combined associated technologies. The guiding premise was
that every functional part of any new design had to have a verifiable scientific reason and
performance, which often resulted in a long evolution.
No functional assumptions were made. All commonly held ideas about what seeds
required were challenged or discarded and new experiments set up to determine their
requirements specifically in untilled soils. This new knowledge was combined with whatever
existing knowledge proved still to be applicable. In other cases the rules for tilled soils
simply did not apply, or were proved wrong, when applied to untilled soils. Undisturbed
soils were found to provide different resources and challenges from those of tilled soils,
thus requiring different approaches to seed sowing.
Other authors report what happened to soil when ploughing ceases. Everyone by now
knows that no-tillage is good and ploughing is bad for the soil, but what are the causal
mechanisms and can the improvements or damage be quantified? Can the gains be further
improved by techniques such as controlled-traffic farming? Still other authors studied
available equipment and management methods and relate these to no-tillage systems and
xiii
applications, large and small. Only when the capabilities of modern no-tillage equipment
are understood and fully integrated into a crop production enterprise can it be fully quantified
and realistic local recommendations made.
Collectively these authors have provided a comprehensive overview of what makes a
successful no-tillage enterprise work. This includes machinery design and operating principles,
the interactions of machines with the soil, the importance of parallel inputs, such as
herbicides, pesticides and controlled traffic, and the management of the system as a whole,
including quantifying the importance of soil carbon and tracking carbon dioxide emissions
as a function of soil disturbance. They have also provided a guide to experimental
procedures for evaluation of variables.
The book is not intended to be a blueprint on how to design any one style of no-tillage
machine, component or system. It is a record of the comparative performances of several
different machine design options and management practices, tested under controlled scientific
conditions, and how these have been found to integrate into a whole no-tillage system.
Much of the information is about the biological performance of machines and soils,
since both primarily perform biological functions. But mechanical performance is not
ignored either. The interface between the two is particularly important.
The reader is invited to place his or her own value on the relevance of the data presented.
The relevance some of the authors placed on the data led to the design of the disc
version of a winged opener, called Cross Slot®. Others will see different things in the data.
However, independent research and field experience have increasingly shown that the
data and the conclusions drawn from them have been remarkably accurate and prophetic.
The relevance of the book is that it illustrates that there are now ways and means to
make no-tillage more fail-safe than tillage and to obtain crop yields not only equal to those
from tillage but, in many cases, superior. Untilled soils contain greater potential to germinate,
establish and grow plants than tilled soils ever did. And, of course, they are much
more environmentally friendly. The problem for humankind has been to learn and understand
how to harness that potential. We hope this book goes some way towards achieving
that objective.
The book expands on the first edition, entitled No-tillage Seeding: Science and Practice
(Baker, Saxton and Ritchie, ISBN 0 85199 103 3, first published by CAB International
in 1996 and reprinted in 2002).
xiv Preface
1 The ‘What’ and ‘Why’ of
No-tillage Farming
C. John Baker and Keith E. Saxton
No farming technique yet devised by
humankind has been anywhere near as
effective as no-tillage at halting soil erosion
and making food production truly
sustainable.
Since the early 1960s farmers have been
urged to adopt some form of conservation
tillage to save the planet’s soil, to reduce the
amount of fossil fuels burnt in growing
food, to reduce runoff pollution of our waterways,
to reduce wind erosion and air quality
degradation and a host of other noble
and genuine causes. Charles Little in Green
Fields Forever (1987) epitomized the genuine
enthusiasm most conservationists have
for the technique. But early farmer experience,
especially with no-tillage, suggested
that adopting such techniques would result
in greater short-term risk of reduced seedling
emergence, crop yield or, worse, crop
failure, which they were being asked to
accept for the long-term gains outlined above.
Farmers of today were unlikely to see
many short-term benefits of their conservation
practices. Leaving a legacy of better
land for future generations was one thing,
but the short-term reality of feeding the
present generation and making a living
was quite another. Not unreasonably, shortterm
expediency often took priority.
Although some countries already produce
50% or more of their food by no-tillage (e.g.
Brazil, Argentina and Paraguay), it is estimated
that, worldwide, no-tillage currently
accounts for only some 5–10% of food
production. We still have a long way to go.
Certainly there have been good, and even
excellent, no-tillage crops, but there have
also been failures. And it is the failures that
take prime position in the minds of all
but the most forward-looking or innovative
farmers.
Tillage has been fundamental to crop
production for centuries to clear and soften
seedbeds and control weeds. So now we are
changing history, not always totally omitting
tillage (although that is certainly a
laudable objective) but significantly altering
the reasons and processes involved.
Most people understand tillage to be a process
of physically manipulating the soil to
achieve weed control, fineness of tilth,
smoothness, aeration, artificial porosity, friability
and optimum moisture content so as
to facilitate the subsequent sowing and covering
of the seed. In the process, the undisturbed
soil is cut, accelerated, impacted,
inverted, squeezed, burst and thrown, in an
effort to break the soil physically and bury
weeds, expose their roots to drying or to
physically destroy them by cutting. The
objective of tillage is to create a weed-free,
smooth, friable soil material through which
© FAO and CAB International 2007. No-tillage Seeding in Conservation
Agriculture, 2nd edn. (eds C.J. Baker and K.E. Saxton) 1
relatively unsophisticated seed drill openers
can travel freely.
During no-tillage, few, if any, of the
processes listed above take place. Under
no-tillage, other weed-control measures,
e.g. chemicals, must substitute for the physical
disturbance during tillage to dislodge,
bury or expose existing weeds. But part of
the tillage objective is also to stimulate new
weed seed germination so that fresh weeds
get an ‘even start’ and can therefore be
easily killed in their juvenile stages by a
single subsequent tillage operation. Notillage,
therefore, must either find another
way of stimulating an ‘even start’ for new
weeds, which would then require a subsequent
application of herbicide or avoid
stimulating new weed growth in the first
place.
In his keynote address to the 1994
World Congress of Soil Science, Nobel
Prize-winner Norman Borlaug estimated
that world cereal production (which accounts
for 69% of world food supply) would
need to be raised by 24% by the year 2000
and doubled by the year 2025. More importantly,
Borlaug estimated that grain yields
would need to increase by 80% over the
same time span because creating new arable
land is severely limited throughout the
world. Until now, yield increases have
come largely from increased fertilizer and
pesticide use and genetic improvement to
the species grown. The challenge is for
no-tillage to contribute to future increases,
while simultaneously achieving resource
preservation and environmental goals. But
this is only going to happen if no-tillage is
practised at advanced technology levels.
The notion of sowing seeds into untilled
soils is very old. The ancient Egyptians practised
it by creating a hole in untilled soil
with a stick, dropping seeds into the hole
and then closing it again by pressing the
sides together with their feet. But it was
not until the 1960s, when the herbicides
paraquat and diquat were released by the
then Imperial Chemical Industries Ltd (now
Syngenta) in England, that the modern
concept of no-tillage was born because
now weeds could be effectively controlled
without tillage.
For the preceding decade it had been
recognized that, for no-tillage to be viable,
weeds had to be controlled by some other
method than tillage. But the range of agricultural
chemicals then available was limited
because of their residual effects in the
soil. A delay of several weeks was necessary
after spraying before the new crop could be
safely sown, which partly negated saving of
time, one of the more noteworthy advantages
of no-tillage compared with tillage.
Paraquat and diquat are almost instantly
deactivated upon contact with soil. When
sprayed onto susceptible living weeds, the
soil beneath is almost instantly ready to
accept new seeds, without the risk of injury.
This breakthrough in chemical weed
control spawned the birth of true no-tillage.
Since then, there have been other broaderspectrum
translocated non-residual chemicals,
such as glyphosate, which was first
introduced as Roundup by Monsanto. Other
generic compounds, such as glyphosate
trimesium (Touchdown) and glufosinate
ammonium (Buster), were later marketed by
other companies, which have expanded the
concept even further.
In other circumstances non-chemical
weed control measures have been used.
These include flame weeding, steam weeding,
knife rolling and mechanical hand
weeding. None of the alternative measures
has yet proved as effective as spraying with a
translocated non-residual herbicide. These
chemicals are translocated to the roots of the
plant thereby affecting a total kill of the plant.
Killing the aerial parts alone often allows
regeneration of non-affected plant parts.
The application of any chemicals
within agricultural food production correctly
raises the question of human and
biological safety. Indeed, many chemicals
must be very carefully applied under very
specific conditions for specific results, just
like any of the modern pharmaceuticals that
assist in cures and controls. Through careful
science, and perhaps some good fortune,
glyphosate has been found to be non-toxic
to any biological species other than green
plants and has been safely used for many
years with virtually no known effects other
than the control of undesired plants.
2 C.J. Baker and K.E. Saxton
An even more recent development
using genetic modification of the crops
themselves has made selected plant varieties
immune to very specific herbicides such
as glyphosate. This unique trait permits
planting the crop without weed concerns
until the crop is well established and then
spraying both the crop and the weeds with a
single pass. The susceptible weeds are eliminated
and the immune crop thrives, making
a full canopy that competes with any
subsequent weed growth, usually through
to harvest. Only selected crops such as
maize and soybean are currently commonly
used in this fashion, but they have already
attained a very significant percentage of the
world’s acreage. With this success, other
important food and fibre crops are being
modified for this capability.
What is No-tillage?
As soon as the modern concept of no-tillage
based on non-residual (and mostly translocated)
herbicides was recognized, everyone,
it seems, invented a new name to
describe the process. ‘No-tillage’, ‘direct drilling’
or ‘direct seeding’ are all terms describing
the sowing of seeds into soil that has not
been previously tilled in any way to form a
‘seedbed’. ‘Direct drilling’ was the first term
used, mainly in England, where the modern
concept of the technique originated in the
1960s. The term ‘no-tillage’ began in North
America soon after, but there has been recent
support for the term ‘direct seeding’ because
of the apparent ambiguity that a negative
word like ‘no’ causes when it is used to
describe a positive process. The terms are
used synonymously in most parts of the
world, as we do in this book.
Some of these names are listed below
with their rationales, some only for historical
interest. After all, it’s the process, not
the name, that’s important.
Chemical fallow, or chem-fallow, describes
a field currently not cropped in which
the weeds have been suppressed by
chemical means.
Chemical ploughing attempted to indicate
that the weed control function usually
attributed to ploughing was being done
by chemicals. The anti-chemical lobby
soon de-popularized such a restrictive
name, which is little used today.
Conservation tillage and conservation agriculture
are the collective umbrella terms
commonly given to no-tillage, minimum
tillage and/or ridge tillage, to denote that
the inclusive practices have a conservation
goal of some nature. Usually, the
retention of at least 30% ground cover by
residues after seeding characterizes the
lower limit of classification for conservation
tillage or conservation agriculture,
but other conservation objectives include
conservation of money, labour, time,
fuel, earthworms, soil water, soil structure
and nutrients. Thus, residue levels
alone do not adequately describe all conservation
tillage or conservation agricultural
practices and benefits.
Disc-drilling reflects the early perception
that no-tillage or direct drilling could
only be achieved with disc drills (a perception
that proved to be erroneous);
thus some started referring to the practice
as disc-drilling. Fortunately the
term has not persisted. Besides, disc
drills are also used in tilled soils.
Drillage was a play on words that suggested
that under no-tillage the seed drill was
in fact tilling the soil and drilling the
seed at the same time. It is not commonly
used.
Minimum tillage, min-till and reduced tillage
all describe the practice of restricting
the amount of general tillage of the
soil to the minimum possible to establish
a new crop and/or effect weed control
or fertilization. The practice lies
somewhere between no-tillage and
conventional tillage. Modern practice
emphasizes the amount of surface residue
retention as an important aim of
minimum or reduced tillage.
No-till is a shortening of no-tillage and is
not encouraged by purists, for grammatical
reasons.
Residue farming describes conservation tillage
practices in which residue retention
‘What’ and ‘Why’ of No-tillage 3
is the primary objective, even though
many of the ‘conservation tillage’ benefits
previously mentioned may also
accrue.
Ridge tillage, or ridge-till, describes the
practice of forming ridges from tilled
soil into which widely spaced row crops
are drilled. Such ridges may remain in
place for several seasons while successive
crops are no-tilled into the ridges,
or they might be re-formed annually.
Sod-seeding, undersowing, oversowing,
overdrilling and underdrilling all refer
to the specific no-tillage practice of
drilling new pasture seeds into existing
pasture swards, collectively referred to
as pasture renovation. The correct use
of the term oversowing does not involve
drilling at all, but rather is the broadcasting
of seed on to the surface of the
ground. Each of the other listed terms
involves drilling of the seed.
Stale seedbed describes an untilled seedbed
that has undergone a period of fallow,
usually (but not exclusively) with
periodic chemical weed control.
Strip tillage, or zone tillage, refers to the
practice of tilling a narrow strip ahead
of (or with) the drill openers, so the
seed is sown into a strip of tilled soil
but the soil between the sown rows
remains undisturbed. ‘Strip tillage’ also
refers to the general tilling of much
wider strips of land (100 or more
metres wide) on the contour, separated
by wide fallowed strips, as an erosioncontrol
measure based on tillage.
Sustainable farming is the end product of
applying no-tillage practices continuously.
Continuous cropping based on
tillage is now considered to be unsustainable
because of resource degradation
and farming inefficiencies, while
continuous cropping based on no-tillage
is much more likely to be sustainable
on a long-term basis under most agricultural
conditions. Some discussions of
‘sustainability’ include broader considerations
beyond the preservation of
natural resources and food production,
such as economics, energy and quality
of life.
Zero-tillage was synonymous with notillage
and is still used to a limited
extent today.
The most commonly identified feature
of no-tillage is that as much as possible of
the surface residue from the previous crop
is left intact on the surface of the ground,
whether this be the flattened or standing
stubble of an arable crop that has been
harvested or a sprayed dense sward of grass.
In the USA, where the broad category of
conservation tillage is generally practised
as an erosion-control measure, the accepted
minimum amount of surface covered by
residue after passage of the drill is 30%.
Most practitioners of the more demanding
option of no-tillage or direct seeding aim for
residue-coverage levels of at least 70%.
Of course, some crops, such as cotton,
soybean and lupin, leave so little residue
after harvest that less than 70% of the
ground is likely to be covered by residue
even before drilling. Such a soil, however,
can be equally well direct drilled as a fully
residue-covered soil in the course of establishing
the next crop. Thus it is also
regarded as true no-tillage. What is no-tillage
to one observer may not be no-tillage to
another, depending upon the terms of reference
and expectations of each observer.
The most fundamental criterion common
to all no-tillage is not the amount of
residue remaining on the soil after drilling,
but whether or not that soil has been
disturbed in any way prior to drilling. Even
then, during drilling, as will be explained
later, such a seemingly unambiguous definition
becomes confused when you consider
the actions of different drills and
openers in the soil. Some literally till a strip
as they go, while others leave all of the soil
almost undisturbed. So the untilled soil
prior to drilling might well become something
quite different after drilling.
This book is focused on the subject of
‘no-tillage’ in which no prior disturbance
or manipulation of the soil has occurred
other than possibly minimal disturbance by
operations such as shallow weed control,
fertilization or loosening of subsurface compacted
layers. Such objectives are entirely
4 C.J. Baker and K.E. Saxton
compatible with true no-tillage. Any disturbance
before seeding is expected to have
had very minimal surface disturbance of
soil or residues.
Depending on the field cropping history
and the available seeding machine capability,
it may be necessary to perform one or
more very minimal-disturbance functions
for best crop performance. The most common
of these needs is the application of fertilizer
when that function can not be made
part of the seeding operation. Early no-tillage
seeding trials often simply broadcast the fertilizer
over the soil surface expecting it to be
carried into the soil profile by precipitation,
but two things became readily apparent.
First, only the nitrogen component was
moved by water, leaving the remaining
forms, such as phosphorus and potassium,
on or near the soil surface. And even then
preferential flow of soluble nitrogen down
earthworm and old root channels often
meant that much of it bypassed the juvenile
roots of the newly sown crop (see Chapter 9).
Secondly, emerging weeds between the
crop plants readily helped themselves as
the first consumers of this fertilizer and
‘outgrew’ the crop. Subsurface placement is
now the only recommended procedure,
often banded near the seeding furrow or
emerging crop row.
Where herbicides are less available, it
may prove more economical to perform a
weeding pass prior to seeding to reduce
the weed pressures on the emerging crop.
If used in conservation agriculture, this
operation must be very shallow and leave
the soil surface and residues nearly intact
ready for the seeding operation. Typical
implements that can achieve this quality of
weed control are shallow-running V-shaped
chisels or careful hand hoeing.
Historical compaction arising from
many years of repetitive tillage often cannot
be undone ‘overnight’ by switching to
no-tillage. While soil microbes are rebuilding
their numbers and improving soil structure,
a process that may take several years
even in the most favourable of climates,
historical compaction may still exist. Temporary
relief can often be achieved by using
a subsoiling machine that cracks and bursts
subsurface zones while causing only minor
disturbance at the surface.
But sometimes overly aggressive subsoilers
cause so much surface disturbance
that full tillage is then required to smooth
the surface again. This seemingly endless
negative spiral must be broken if the benefits
of no-tillage are to be gained. All that
is required is a less aggressive or shallowacting
subsoiler that allows no-tillage to
take place after its passage without any
further ‘working’ of the soil surface layer.
Another effective method is to sow a
grass or pasture species in the compacted
field and either graze this with light stocking
or leave it ungrazed as a ‘set-aside’ area
for a number of years before embarking on a
no-tillage programme thereafter without
tillage. A rule of thumb for how many years
of pasture are required to restore soil
organic carbon (SOC) and ultimately the
structural damage done by tillage was established
by Shepherd et al. (2006) for a gley
soil (Kairanga silty clay loam) under maize
in New Zealand soils as:
Where tillage has been undertaken for up to
4 consecutive years, it takes approximately
11years of pasture to restore SOC levels
for each year of tillage.
Where tillage has been undertaken for
more than 4 consecutive years, it takes up
to 3 years of pasture to restore SOC levels
for each year of tillage.
The rate of recovery of soil structure lags
behind the recovery rate of SOC. The more
degraded the soil, the greater the lag time.
Why No-tillage?
It is not the purpose of this book to explore
in detail the advantages and disadvantages
of either no-tillage or conservation tillage.
Numerous authors have undertaken this
task since Edward Faulkner and Alsiter
Bevin questioned the wisdom of ploughing
in Ploughman’s Folly (Faulkner, 1943) and
The Awakening (Bevin, 1944). Although
neither of these authors actually advocated
no-tillage, it is interesting to note that
Faulkner made the now prophetic observation
that ‘no one has ever advanced a
‘What’ and ‘Why’ of No-tillage 5
scientific reason for ploughing’. In fact, long
before Faulkner’s and Bevin’s time, the
ancient Peruvians, Scots, North American
Indians and Pacific Polynesians are all
reported to have practised a form of conservation
tillage (Graves, 1994).
None the less, to realistically focus
on the methods and mechanization of notillage
technologies, it is useful to compare
the advantages and disadvantages of
the technique in general as measured
against commonly practised tillage farming.
The more common of these are summarized
below with no particular order or priority.
Those followed by an ∗ can be either an
advantage or a disadvantage in differing
circumstances.
In Chapter 2 we shall expand on the
advantages (benefits) of no-tillage, particularly
those derived either directly or indirectly
from enhancement of SOC levels, and
in Chapter 3 we shall examine the risks of
no-tillage in more detail.
Advantages
Fuel conservation. Up to 80% of fuel used
to establish a crop is conserved by converting
from tillage to no-tillage.
Time conservation. The one to three trips
over a field with no-tillage (spraying,
drilling and perhaps subsoiling) results
in a huge saving in time to establish a
crop compared with the five to ten trips
for tillage plus fallow periods during
the tillage process.
Labour conservation. Up to 60% fewer
person-hours are used per hectare compared
with tillage.
Time flexibility. No-tillage allows late decisions
to be made about growing crops
in a given field and/or season.
Increased soil organic matter. By leaving
the previous crop residues on the soil
surface to decay, soil organic matter
near the surface is increased, which in
turn provides food for the soil microbes
that are the builders of soil structure.
Tillage oxidizes organic matter, resulting
in a cumulative reduction, often
more than is gained from incorporation.
Increased soil nitrogen. All tillage mineralizes
soil nitrogen, which may provide a
short-term boost to plant growth, but
such nitrogen is ‘mined’ from the soil
organic matter, further reducing total
soil organic matter levels.
Preservation of soil structure. All tillage
destroys natural soil structure while
no-tillage minimizes structural breakdown
and increases organic matter and
humus to begin the rebuilding process.
Preservation of earthworms and other soil
fauna. As with soil structure, tillage
destroys humans’ most valuable soilborne
ally, earthworms, while no-tillage
encourages their multiplication.
Improved aeration. Contrary to early predictions,
the improvement in earthworm
numbers, organic matter and soil structure
usually result in improved soil
aeration and porosity over time. Soils do
not become progressively harder and
more compact. Quite the reverse occurs,
usually after 2–4 years of no-tillage.
Improved infiltration. The same factors that
aerate the soil result in improved infiltration
into the soil. Plus residues reduce
surface sealing by raindrop impact and
slow down the velocity of runoff water.
Preventing soil erosion. The sum of preserving
soil structure, earthworms and
organic matter, together with leaving
the surface residues to protect the soil
surface and increase infiltration, is to
reduce wind and water soil erosion
more than any other crop-production
technique yet devised by humans.
Soil moisture conservation. Every physical
disturbance of the soil exposes it to drying,
whereas no-tillage and surface residues
greatly reduce drying. In addition,
accumulation of soil organic matter
greatly improves the water-holding
capacity of soils.
Reduced irrigation requirements. Improved
water-holding capacity and reduced
evaporation from soils lessen the need
for irrigation, especially at early stages
of growth when irrigation efficiency is
at its lowest.
Moderating soil temperatures.* Under notillage
soil temperatures in summer
6 C.J. Baker and K.E. Saxton
stay lower than under tillage. Winter
temperatures are higher where snow
retention by residue is a factor, but
spring temperatures may rise more
slowly.
Reduced germination of weeds. The absence
of physical soil disturbance under notillage
reduces stimulation of new
weed seed germination, but the in-row
effect of this factor is highly dependent
on the amount of disturbance caused by
the no-tillage openers themselves.
Improved internal drainage. Improved
structure, organic matter, aeration and
earthworm activity increase natural
drainage within most soils.
Reduced pollution of waterways. The
decreased runoff of water from soil and
the chemicals it transports reduces
pollution of streams and rivers.
Improved trafficability. Untilled soils are
capable of withstanding vehicle and
animal traffic with less compaction and
structural damage than tilled soils.
Lower costs. The total capital and/or operating
costs of all machinery required to
establish tillage crops are reduced by
up to 50% when no-tillage substitutes
for tillage.
Longer replacement intervals for machinery.*
Because of reduced hours per
hectare per year, tractors and advanced
no-tillage drills are replaced less often
and reduce capital costs over time.
Some lighter no-tillage drills, however,
may wear out more quickly than their
tillage counterparts because of the
greater stresses involved in operating
them in untilled soils.
Reduced skills level.* While achieving successful
no-tillage is a skilful task in
itself, the total range of skills required
is smaller than the many sequential tasks
needed to complete successful tillage.
Natural mixing of soil potassium and phosphorus.
Earthworms mix large quantities
of soil potassium and phosphorus in
the root zone, which favours no-tillage
because it sustains earthworm numbers
and increases plant nutrient availability.
Less damage of new pastures. The more
stable soil structure of untilled soils
allows quicker utilization of new
pastures by stock with less plant disruption
during early grazing than
where tillage has been employed.
More recreation and management time. The
time otherwise devoted to tillage can be
used to advantage for further management
inputs (including the farming of
more land) or for family and recreation.
Increased crop yields. All of the above factors
are capable of improving crop yields
to levels well above those attained by
tillage – but only if the no-tillage system
and processes are fully practised without
short cuts or deficiencies.
Future improvements expected. Modern
advanced no-tillage systems and equipment
have removed earlier expectations
of depressed crop yields in the
short term to gain the longer-term benefits
of no-tillage. Ongoing research and
experience have developed systems that
eliminate short-term depressed yields
while at the same time raising the
expectation and magnitudes of yield
increases in the medium to longer term.
Disadvantages
Risk of crop failure.* Where inappropriate
no-tillage tools and weed- or pestcontrol
measures are used, there will be
a greater risk of crop yield reductions
or failure than for tillage. But where
more sophisticated no-tillage tools and
correct weed- and pest-control measures
are used, the risks will be less than for
tillage.
Larger tractors required.* Although the total
energy input is significantly reduced
by changing to no-tillage, most of that
input is applied in one single operation,
drilling, which may require a
larger tractor or more animal power, or
conversely a narrower drill.
New machinery required. Because no-tillage
is a relatively new technique, new and
different equipment has to be purchased,
leased or hired.
New pest and disease problems.* The
absence of physical disturbance and
‘What’ and ‘Why’ of No-tillage 7
retention of surface residues encourages
some pests and diseases and changes
the habitats of others. But such conditions
also encourage their predators. To
date, no pest or disease problems have
proved to be insurmountable or untreatable
in long-term no-tillage systems.
Fields are not smoothed. The absence of
physical disturbance prevents soil
movement by machines for smoothing
and levelling purposes. This puts pressure
on no-tillage drill designers to create
machines that can cope with
uneven soil surfaces. Some do this
better than others.
Soil strength may vary across fields. Tillage
serves to create a consistently low soil
strength across each field. Long-term
no-tillage requires machines to be capable
of adjusting to natural variations in
soil strength that occur across every
field. Since soil strength dictates the
penetration forces required to be applied
to each no-tillage opener, variable
soil strength places particular demands
on drill designs if consistent seeding
depths and seed coverage are to be
attained.
Fertilizers are more difficult to incorporate.*
General incorporation of fertilizers
is more difficult in the absence of
physical burial by machines, but specific
incorporation at the time of drilling
is possible and desirable, using
special designs of no-tillage openers.
Pesticides are more difficult to incorporate.
As with fertilizers, general incorporation
of pesticides (especially those that
require pre-plant soil incorporation) is
not readily possible with no-tillage,
requiring different pest-control strategies
and formulations.
Altered root systems.* The root systems of
no-tillage crops may occupy smaller
volumes of soil than under tillage,
but the total biomass and function of
the roots are seldom different and
anchorage may in fact be improved.
Altered availability of nitrogen.* There are
three factors that affect nitrogen availability
during early plant development
under no-tillage:
The decomposition of organic matter
by soil microbes often temporarily
‘locks up’ nitrogen, making it less plantavailable
under no-tillage.
No-tillage reduces mineralization
of soil organic nitrogen that tillage otherwise
releases.
The development of bio-channels
in the soil from earthworms and roots
causes preferential flow of surfaceapplied
nitrogenous fertilizers into the
soil, which may bypass shallow, young
crop roots.
Each (or all) of these factors may create
a nitrogen deficiency for seedlings,
which encourages placing nitrogen with
drilling. Fortunately some advanced
no-tillage drills have separate nitrogen
banding capabilities that overcome this
problem.
Use of agricultural chemicals.* The reliance
of no-tillage on herbicides for weed
control is a cost and environmental
negative but is offset by the reduction
in surface runoff of other chemical pollutants
(including surface-applied fertilizers)
and the fact that most of the
primary chemicals used in no-tillage
are ‘environmentally friendly’. Smallscale
agriculture may require more
hand weeding, but with greater ease
than with tilled soils.
Shift in dominant weed species.* Chemical
weed control tends to be selective
towards weeds that are resistant to the
range of available formulations, requiring
more diligent use of crop rotations
by farmers and commitment by the agricultural
chemical industry to researching
new formulations.
Restricted distribution of soil phosphorus.*
Relatively immobile soil phosphorus
tends to become distributed in a narrower
band within the upper soil layers
under no-tillage because of the absence
of physical mixing. Improved earthworm
populations help reduce this
effect and also cycle nutrient sources
situated below normal tillage levels.
New skills are required.* No-tillage is a
more exacting farming method, requiring
8 C.J. Baker and K.E. Saxton
the learning and implementation of
new skills, and these are not always
compatible with existing tillage-related
skills or attitudes.
Increased management and machine performance.
There is only one opportunity
with each crop to ‘get it right’ under
a no-tillage regime. Because no-tillage
drilling is literally a once-over operation,
there is less room for error compared
with the sequential operations
involved in tillage. This places emphasis
on the tolerance of no-tillage drills
to varying operator skill levels and
their ability to function effectively in
suboptimal conditions.
No-tillage drill selection is critical.* Few
farmers can afford to own several different
no-tillage drills awaiting the
most suitable conditions before selecting
which one to use. Fortunately more
advanced no-tillage drills are capable
of functioning consistently in a wider
range of conditions than most tillage
tools, making reliance on a single notillage
drill for widely varying conditions
both feasible and a practical
reality.
Availability of expertise. Until the many specific
requirements of successful no-tillage
are fully understood by ‘experts’, the
quality of advice to practitioners from
consultants will remain, at best, variable.
Local, successful no-tillage farmers
often become the best advisers.
Untidy field appearance.* Farmers who
have become used to the appearance of
neat, ‘clean’, tilled seedbeds often find
the retention of surface residues (‘trash’)
‘untidy’. But, as they come to appreciate
the economic advantages of true notillage,
many such farmers gradually
come to see residues as an important
resource rather than ‘trash’ requiring
disposal.
Elimination of ‘recreational tillage’.* Some
farmers find driving big tractors and
tilling on a large scale to be recreational.
Others regard it as a chore and
health-damaging. Farmers in developing
countries regard tillage as burdensome
or impossible.
Figure 1.1 shows some of the likely shortand
long-term trends that might arise as a
result of converting from tillage to no-tillage.
‘What’ and ‘Why’ of No-tillage 9
Fig. 1.1. The likely short- and long-term trends that might arise as a result of converting from tillage to
no-tillage (from Carter, 1994).
Each identified item or process progresses
over the years from stopping tillage as the
effects of no-tillage take precedent. The
realization is that the effects of no-tillage
are developed as the soil and its physical
and biological characteristics change.
The result of these combined processes has
been observed and documented in nearly
every soil and climate worldwide, to the
point of becoming common knowledge. It is
in this transition stage that many who convert
to no-tillage farming become disillusioned
and sceptical that the benefits will
in fact occur.
Summary of the ‘What’ and ‘Why’
of No-tillage
No-tillage farming is a significant methodology
shift in production farming as performed
over the past 100 years of mechanized agriculture.
It intuitively requires new thinking
by the producers of the ‘what’ and ‘why’
to change the processes. Only by encompassing
the full scope of ‘why’ we should
change from an enormously successful
food production system shall we move forward
with confidence to develop ‘what’
a modern no-tillage farming system should
incorporate. The short-term advantages
far outweigh the disadvantages, and in the
longer term it involves no less than making
world food production sustainable for the
first time in history.
10 C.J. Baker and K.E. Saxton
2 The Benefits of No-tillage
Don C. Reicosky and Keith E. Saxton
Intensive tillage farming reduces soil organic
matter and degrades soil quality – no-tillage
farming enhances soil quality and sustains
long-term agriculture.
Introduction
Sustainable food and fibre production of
any given field and region requires that the
farming methods be economically competitive
and environmentally friendly. To achieve
this result requires adopting a farming technology
that not only benefits production
but provides an environmental benefit to
the long-term maintenance of the soil and
water resources upon which it is based. We
must reduce pollution and use our resources
in line with the earth’s carrying capacity for
sustainable production of food and fibre.
The responsibility of sustainable agriculture
lies on the shoulders of farmers to
maintain a delicate balance between the
economic implications of farming practices
and the environmental consequences of
using the wrong practices. This responsibility
entails producing food and fibre to meet
the increasing population while maintaining
the environment for a sustained high quality
of life. The social value of an agricultural
community is not just in production,
but in producing in harmony with nature
for improved soil, water and air quality and
biological diversity.
Sustainable agriculture is a broad concept
that requires interpretation at the regional
and local level. The principles are captured
in the definition reported by El-Swaify
(1999) as: ‘Sustainable agriculture involves
the successful management of resources for
agriculture to satisfy changing human needs,
while maintaining or enhancing the quality
of the environment and conserving natural
resources.’
Conservation agriculture, especially
no-tillage (direct seeding), has been proved
to provide sustainable farming in many
agricultural environments virtually around
the world. The conditions and farming scales
vary from humid to arid and vegetable plots
to large prairie enterprises. All employ and
adapt very similar principles but with a
wide variety of machines, methods and
economics.
The benefits of performing crop production
with a no-tillage farming system are
manyfold. Broad subjects discussed here
only begin to provide the science and results
learned over recent decades of exploring
and developing this farming method. In
addition to improved production and soil
and water resource protection, many other
benefits accrue. For example, it saves time
and money, improves timing of planting
© FAO and CAB International 2007. No-tillage Seeding in Conservation
Agriculture, 2nd edn. (eds C.J. Baker and K.E. Saxton) 11
and harvesting, increases the potential for
double cropping, conserves soil water through
decreased evaporation and increased
infiltration, reduces fuel, labour and machinery
requirements and enhances the global
environment.
Principles of Conservation
Agriculture
Conservation agriculture requires implementing
three principles, or pillars, as illustrated
in Fig. 2.1. These are: (i) minimum
soil tillage disturbance; (ii) diverse crop
rotations and cover crops; and (iii) continuous
plant residue cover. The main direct
benefit of conservation agriculture and direct
seeding is increased soil organic matter and
its impact on the many processes that determine
soil quality. The foundation underlying
the three principles is their contribution
and interactions with soil carbon, the primary
determinant of long-term sustainable
soil quality and crop production.
Conservation tillage includes the concepts
of no-tillage, zero-tillage and direct
seeding as the ultimate form of conservation
agriculture. These terms are often used
interchangeably to denote minimum soil
disturbance. Reduced tillage methods, sometimes
referred to as conservation tillage,
such as strip tillage, ridge tillage and mulch
tillage, disturb a small volume of soil and
partially mix the residue with the soil and
are intermediate in their soil quality effects.
These terms define the tillage equipment
and operation characteristics as they relate
to the soil volume disturbed and the degree
of soil–residue mixing. Intensive inversion
tillage, such as that from mouldboardploughing,
disc-harrowing and certain types
of powered rotary tillage, is not a form of
conservation tillage. No-tillage and direct
seeding are the primary methods of conservation
tillage to apply the three pillars of
conservation agriculture for enhanced soil
carbon and its associated environmental
benefits.
True soil conservation is largely related
to organic matter, i.e. carbon, management.
12 D.C. Reicosky and K.E. Saxton
Fig. 2.1. Schematic representation of the three pillars or principles of conservation agriculture
supported by a foundation of soil carbon.
By nothing more than properly managing
the carbon in our agricultural ecosystems,
we can have less erosion, less pollution,
clean water, fresh air, healthy soil, natural
fertility, higher productivity, carbon credits,
beautiful landscapes and sustainability.
Dynamic soil quality encompasses those
properties that can change over relatively
short time periods, such as soil organic
matter, soil structure and macroporosity.
These can readily be influenced by the
actions of human use and management
within the chosen agronomic practices.
Soil organic matter is particularly dynamic,
with inputs of plant materials and losses by
decomposition.
Crop Production Benefits
Producing a crop and making an economic
profit are universal goals of global farming.
Production by applying no-tillage methods
is no different in these goals, but there are
definite benefits for the achievement, which
we outline in this chapter. But these benefits
only occur with fully successful no-tillage
farming. There are certainly obstacles and
risks in moving from traditional tillage
farming, which has been the foundation
technology for centuries, as outlined in
Chapter 3.
Acceptable crop production requires
an adequate plant stand, good nutrition and
moisture with proper protection from weed,
insect or disease competition. Achieving
the plant stand in untilled, residue-covered
soils is the first major obstacle, a particular
challenge inmodernmechanized agriculture,
but certainly surmountable, as explained
in the core of this text. Providing adequate
nutrition and water for full crop potentials
is readily achieved with the benefits of
no-tillage, as discussed below.
Weed-control methods, by necessity,
shift to dependence on chemicals, flameweeding,
mechanical crushing or hand
picking for full no-tillage farming to stay
within the goal of minimum soil disturbance.
Chemical developments in recent
decades have made great strides in their
effectiveness, environmental friendliness
and economic feasibility. Supplemental techniques
of mowing, rolling and crushing
without soil disturbance are showing significant
promise to reduce weed presence and
increase the benefit of cover crops and residues.
Experience has shown that controlling
insects and diseases has generally been
less of a problem with no-tillage, even though
there are often dire predictions about the
potential impact of surface residues harbouring
undesirables. As with weeds, crop
health and pest problems are not likely to
be avoided but may well shift to new varieties
and species with the change in the field
environment.
As a result of these developments and
skilled applications, it has been repeatedly
shown that crop production can be equalled
and exceeded by no-tillage farming compared
with traditional tillage methods. Because
many soils have been tilled for many years,
it is not uncommon to experience some yield
reduction in the first few no-tillage years,
largely because, as discussed later, it takes
time for the soil to rebuild into a higher quality.
This ‘transition period reduction’ can
often be overcome or even averted with
increased fertility, strategic fertilizer banding
with drill openers and careful crop
selection.
The full benefit of no-tillage comes in
the reduced inputs. Most notable are the
reduced inputs by minimizing labour and
machine hours spent establishing and maintaining
the crop. Reduced machine costs
alone are significant, since all tillage equipment
is dispensable. True no-tillage farming
requires only an effective chemical sprayer,
seeding–fertilizing drill and harvester.
With no seedbed preparation of the
soil by tillage, seed drilling has become the
major limitation to many efforts to successfully
change to no-tillage farming.Modifying
drills used in tillage farming has generally
not been very successful, resulting in
undesirable crop stands for optimum production.
Many were not equipped to provide
simultaneous fertilizer banding; thus
it had to be provided by a supplemental
minimum-tillage machine or, in the worst
case, surface-applied, where it was very
ineffective and stimulated weed growth.
Benefits of No-tillage 13
Fortunately, drill development has progressed
to now provide acceptable seeding
in many cases, but, as described in later
chapters, many still do not fully meet all
desirable attributes, especially in relation to
the amount of soil disturbance they create.
As a result of science and technique
developments of recent years, no-tillage
crop production now not only is feasible
but has significant economic benefits. Combining
and multiplying this result by the
further benefits of soil and environmental
qualities make no-tillage farming a highly
desirable method of crop production.
Further, many are now finding personal
and social benefits from the reduced
labour inputs, which remove much of the
demanded time and drudgery often associated
with traditional farm life. A common
remark by successful no-tillage farmers is ‘It
has brought back the fun of farming.’
Increased organic matter
Understanding the role of soil organic matter
and biodiversity in agricultural ecosystems
has highlighted the value and importance
of a range of processes that maintain and
fulfil human needs. Soil organic matter is so
valuable for its influence on soil organisms
and properties that it can be referred to
as ‘black gold’ because of its vital role in
physical, chemical and biological properties
and processes within the soil system.
The changes of these basic soil properties,
called ‘ecosystem services’, are the processes
by which the environment produces
resources that sustain life and which we
often take for granted. An ecosystem is a community
of animals and plants interacting
with one another within their physical
environment. Ecosystems include physical,
chemical and biological components such
as soils, water and nutrients that support the
biological organisms living within them,
including people. Agricultural ecosystem
services include production of food, fibre
and biological fuels, provision of clean air
and water, natural fertilization, nutrient
cycling in soils and many other fundamental
life support services. These services may
be enhanced by increasing the amount of
carbon stored in soils.
Conservation agriculture through its
impact on soil carbon is the best way to
enhance ecosystem services. Recent analyses
have estimated national and global economic
benefits from ecosystem services of soil formation,
nitrogen fixation, organic matter
decomposition, pest biocontrol, pollination
and many others. Intensive agricultural
management practices cause damage or loss
of ecosystem services, by changing such
processes as nutrient cycling, productivity
and species diversity (Smith et al., 2000).
Soil carbon plays a critical role in the harmony
of our ecosystems providing these services.
Soil carbon is a principal factor in maintaining
a balance between economic and
environmental factors. Its importance can
be represented by the central hub of a wagon
wheel, a symbol of strength, unity and progress
(Reicosky, 2001a). The ‘spokes’ of this
wheel in Fig. 2.2 represent incremental
links to soil carbon that lead to the environmental
improvement that supports total soil
resource sustainability. Many spokes make
a strong wheel. Each of the secondary
benefits that emanate from soil carbon
contributes to environmental enhancement
through improved soil carbon management.
Soane (1990) discussed several practical
aspects of soil carbon important in soil
management. Some of the ‘spokes’ of the
environmental sustainability wheel are
described in the following paragraphs.
Based on soil carbon losses with intensive
agriculture, reversing the decreasing
soil carbon trend with less tillage intensity
benefits a sustainable agriculture and the
global population by gaining better control
of the global carbon balance. The literature
holds considerable evidence that intensive
tillage decreases soil carbon and supports
increased adoption of new and improved
forms of no-tillage to preserve or increase
storage of soil organic matter (Paustian
et al., 1997a, b; Lal et al., 1998). The environmental
and economic benefits of conservation
agriculture and no-tillage demand their
consideration in the development of
improved soil carbon storage practices for
sustainable production.
14 D.C. Reicosky and K.E. Saxton
Increased available soil water
Increased soil organic matter has a significant
effect on soil water management because of
increased infiltration and water-holding
capacity. Enhanced soil water-holding capacity
is a result of increased soil organic matter,
which more readily absorbs water and
releases it slowly over the season to minimize
the impacts of short-term drought. Hudson
(1994) showed that, for some soil textures, for
each 1% weight increase in soil organic matter,
the available water-holding capacity in
the soil increased by 3.7% volume. Other
factors being equal, soils containing more
organic matter can retain more water from
each rainfall event and make more of it available
to plants. This factor and the increased
infiltration with higher organic matter and
the decreased evaporation with crop residues
on the soil surface all contribute to improved
water use efficiency.
Increased organic matter is known to
increase soil infiltration and water-holding
capacity, which significantly affect soil water
management. Under these situations, crop
residues slow runoff water and increase infiltration
by earthworm channels, macropores
and plant root holes (Edwards et al., 1988).
Water infiltration is two to ten times faster
in soils with earthworms than in soils without
earthworms (Lee, 1985).
Soil organic matter contributes to soil
particle aggregation, which makes it easier
for water to move through the soil and
enables plants to use less energy to establish
root systems (Chaney and Swift, 1984).
Intensive tillage breaks up soil structure and
results in a dense soil, making it more difficult
for plants to fully access the nutrients
and water required for their growth and
production. No-tillage and minimum-tillage
farming allows the soil to restructure and
accumulate organic matter for improved
plant water and nutrient availability.
Reduced soil erosion
Crop residue management practices have
included many agricultural practices to
reduce soil erosion runoff and off-site sedimentation.
Soils relatively high in C, particularly
with crop residues on the soil surface,
very effectively increase soil organic matter
and reduce soil erosion loss. The primary
role of soil organic matter to reduce soil erodibility
is to stabilize the surface aggregates
Benefits of No-tillage 15
Fig. 2.2. Environmental sustainability wheel with benefits emanating from the soil carbon hub.
through reduced crust formation and surface
sealing, resulting in less runoff (Le
Bissonnais, 1990). Reducing or eliminating
runoff that carries sediment from fields to
rivers and streams is a major enhancement
of environmental quality. Under these situations,
crop residues act as tiny dams that
slow down water runoff from fields, allowing
thewatermore time to soak into the soil.
Crop residues on the surface not only
help hold soil particles in place but keep
associated nutrients and pesticides on the
field. The surface layer of organic matter
minimizes herbicide runoff and, with conservation
tillage, herbicide leaching can be
reduced by as much as half (Braverman
et al., 1990).
Increased soil organic matter and crop
residues on the surface will significantly
reduce wind erosion (Skidmore et al., 1979).
Depending on the amount of crop residues
left on the soil surface, soil erosion can be
reduced to near zero as compared with that
from an unprotected, intensively tilled field.
Wind or water soil erosion causes soil degradation
and variability to the extent of a
resulting crop yield decline.
Papendick et al. (1983) reported that the
original topsoil on most hilltops had been
removed by tillage erosion in the Palouse
region of the Pacific Northwest of the USA.
Mouldboard ploughs were identified as the
primary cause, but all tillage implements
will contribute to this problem (Groves
et al., 1994; Lobb and Kachanoski, 1999).
Soil translocation from mouldboard ploughbased
tillage can be greater than soil loss
tolerance levels (Lindstrom et al., 1992;
Groves et al., 1994; Lobb et al., 1995, 2000;
Poesen et al., 1997). Soil is not directly lost
from the fields by tillage translocation; rather,
it is moved away from the convex slopes
and deposited on concave slope positions.
Lindstrom et al. (1992) showed that
soil movement on a convex slope in southwestern
Minnesota, USA, could result in a
sustained soil loss level of approximately
30 t/ha/year from annual mouldboardploughing.
Lobb et al. (1995) estimated soil
loss in southwestern Ontario, Canada, from
a shoulder position to be 54 t/ha/year from a
tillage sequence of mouldboard-ploughing,
tandem-discing and C-tine cultivating. In
this case, tillage erosion, as estimated through
resident caesium-137, accounted for at least
70% of the total soil loss. The net effect of
soil translocation from the combined effects
of tillage and water erosion is an increase in
spatial variability of crop yield and a likely
decline in soil carbon, related to lower soil
productivity (Schumacher et al., 1999).
Enhanced soil quality
Soil quality is the fundamental foundation
of environmental quality. Soil quality is
largely governed by soil organic matter (SOM)
content, which is dynamic and responds
effectively to changes in soil management,
tillage and plant production. Maintaining
soil quality can reduce the problems of land
degradation, decreasing soil fertility and
rapidly declining production levels that
occur in large parts of the world needing the
basic principles of good farming practice.
Soil compaction in conservation tillage
farming is significantly reduced by the reduction
of traffic and increased SOM (Angers
and Simard, 1986; Avnimelech and Cohen,
1988). Soane (1990) presented several mechanisms
by which soil ‘compactibility’ can be
affected by SOM:
1. Improved internal and external binding
of soil aggregates.
2. Increased soil elasticity and rebounding
capabilities.
3. Reduced bulk density due to mixing
organic residues with the soil matrix.
4. Temporary or permanent existence of
root networks.
5. Localized change of electrical charge of
soil particle surfaces.
6. Change in soil internal friction.
While most soil compaction occurs
during the first vehicle trip over the tilled
field, reduced weight and horsepower
requirements associated with no-tillage can
also help minimize compaction. Additional
field traffic required by intensive tillage
compounds the problem by breaking down
soil structure. Maintenance of SOM
16 D.C. Reicosky and K.E. Saxton
contributes to the formation and stabilization
of soil structure. The combined physical
and biological benefits of SOM can
minimize the effect of traffic compaction
and result in improved soil tilth.
While it is commonly known that tillage
produces a well-fractured soil, sometimes
requiring several tillage passes, it is a misconception
that this is a well-aggregated,
healthy soil. These soils never fare well
when judged against modern knowledge of
high ‘soil quality’. A tilled soil is poorly
structured, is void of many microorganisms
and has poor water characteristics, just to
name a few characteristics. As soils are farmed
without tillage and supplied with residues,
they naturally improve in overall quality,
again support many microorganisms and
become ‘mellow’ to the point of being easily
penetrated by roots and earthworms. This
transition takes several years to accomplish
but invariably occurs given the opportunity.
Many traditional experienced farmers
will often ask, ‘How many years of no-tillage
are possible before the soil becomes so compact
as to require tillage?’ No-tillage experience
has shown exactly the opposite effect:
once a no-tilled soil has regained its quality,
it will continue to resist compaction and
any subsequent tillage will cause undue
damage. Most soils will continue to build
organic matter and improve in quality criteria
for years into the practice of no-tillage
farming if the sequence is not broken by the
thunderous effect of tillage.
Improved nutrient cycles
Improved soil tilth, structure and aggregate
stability enhance the gas exchange and aeration
required for nutrient cycling (Chaney
and Swift, 1984). Critical management of
soil airflow, with improved soil tilth and
structure, is required for optimum plant
function. It is the combination of many
factors that results in comprehensive environmental
benefits from SOM management.
The many attributes suggest new
concepts on how we should manage the
soil for long-term aggregate stability and
sustainability.
Ion adsorption or exchange is one of the
most significant nutrient cycling functions
of soils. Cation exchange capacity (CEC) is
the quantity of exchange sites that can absorb
and release nutrient cations. SOM can
increase this capacity of the soil from 20 to
70%over that of the clay minerals and metal
oxides present. In fact, Crovetto (1996)
showed that the contribution of organic
matter to the cation exchange capacity
exceeded that of the kaolinite clay mineral
in the surface 5 cm of his soils. Robert (1996)
showed that there was a strong linear relationship
between organic carbon and the
cation exchange capacity of his experimental
soil. The capacity was increased fourfold
with an organic carbon increase from 1 to
4%. The toxicity of other elements can be
inhibited by SOM, which has the ability to
adsorb soluble chemicals. Adsorption by
clay minerals and SOM is an important
means by which plant nutrients are retained
in crop rooting zones.
Increased infiltration and concerns over
the use of nitrogen in no-tillage agriculture
require an understanding of the biological,
chemical and physical factors controlling
nitrogen losses and the relative impacts
of contrasting crop production practices
on nitrate leaching from agroecosystems.
Domínguez et al. (2004) evaluated the
leaching of water and nitrogen in plots with
varying earthworm populations in a maize
system. They found that the total flux of
nitrogen in soil leachates was 2.5-fold greater
in plots with increased earthworm populations
than in those with lower populations.
Their results are dependent on rainfall
amounts, but do indicate that earthworms
can increase the leaching of water and inorganic
nitrogen to greater depths in the profile,
potentially increasing nitrogen leaching
from the system. Leaching losses were lower
on the organically fertilized plots, attributed
to higher immobilization potential.
Reduced energy requirements
Energy is required for all agricultural operations.
Modern, intensive agriculture requires
much more energy input than traditional
Benefits of No-tillage 17
farming methods since it relies on the use of
fossil fuels for tillage, transportation, grain
drying and the manufacture of fertilizers,
pesticides and equipment used to apply
agricultural inputs and for generating electricity
used on farms (Frye, 1984). Reduced
labour and machinery costs are economic
considerations that are frequently given
as additional reasons to use conservation
tillage practices.
Practices that require lower energy
inputs, such as no-tillage versus conventional
tillage, generally result in lower inputs of
fuel and a consequent decreases of CO2-
carbon emissions into the atmosphere per
unit of land area under cultivation. Emissions
of CO2 from agriculture are generated from
four primary sources: manufacture and use
of machinery for cultivation, production
and application of fertilizers and pesticides,
the soil organic carbon that is oxidized
following soil disturbance (which is largely
dependent on tillage practices) and energy
required for irrigation and grain drying.
A dynamic part of soil carbon cycling in
conservation agriculture is directly related to
the ‘biological carbon’ cycle, which is differentiated
from the ‘fossil carbon’ cycle.
Fossil carbon sequestration entails the capture
and storage of fossil-fuel carbon prior
to its release to the atmosphere. Biological
carbon sequestration entails the capture of
carbon from the atmosphere by plants. Fossil
fuels (fossil carbon) are very old geologically,
as much as 200 million years. Biofuels
(bio-carbon) are very young geologically
and can vary from 1 to 10 years in age and
as a result can be effectively managed for
improved carbon cycling. One example of
biological carbon cycling is the agricultural
production of biomass for fuel. The major
strength of biofuels is the potential to reduce
net CO2 emissions to the atmosphere.
Enhanced carbon management in conservation
agriculture may make it possible to
take CO2 released from the fossil carbon
cycle and transfer it to the biological carbon
cycle to enhance food, fibre and biofuel
production, for example, using natural gas
fertilizer for plant production.
West and Marland (2002) conducted a
carbon and energy analysis for agricultural
inputs, resulting in estimates of net carbon
flux for three crop types across three tillage
intensities. The analysis included estimates
of energy use and carbon emissions for
primary fuels, electricity, fertilizers, lime,
pesticides, irrigation, seed production and
farm machinery. They estimated that net
CO2-carbon emissions for crop production
with conservation, reduced and no-tillage
practices were 72, 45 and 23 kg carbon/ha/
year, respectively.
Total carbon emission values were used
in conjunction with carbon sequestration
estimates to model net carbon flux to the
atmosphere over time. Based on US average
crop inputs, no-tillage emitted less CO2
from agricultural operations than did conventional
tillage, with 137 and 168 kg of
carbon/ha/year, respectively. The effect of
changes in fossil-fuel use was the dominant
factor 40 years after conversion to no-tillage.
This analysis of US data suggests that,
on average, a change from conventional tillage
to no-tillage will result in carbon sequestration
in soil, plus a saving in CO2
emissions from energy use in agriculture.
While the enhanced carbon sequestration
will continue for a finite time until a new
equilibrium is reached, the reduction in net
CO2 flux to the atmosphere, caused by the
reduced fossil-fuel use, can continue indefinitely,
as long as the alternative practices
are continued.
Lal (2004) recently provided a synthesis
of energy use in farm operations and its
conversion into carbon equivalents (CE).
The principal advantage of expressing energy
use in terms of carbon emission as kg CE lies
in its direct relation to the rate of enrichment
of atmospheric CO2 concentration. The
operations analysed were carbon-intensive
agricultural practices that included tillage,
spraying chemicals, seeding, harvesting,
fertilizer nutrients, lime, pesticide manufacture
and irrigation. The emissions for different
tillage methods were 35.3, 7.9 and 5.8 kg
CE/ha for conventional tillage, chisel tillage
or minimum tillage and no-tillage methods
of seedbed preparation, respectively.
Tillage and harvest operations account
for the greatest proportion of fuel consumption
within intensive agricultural systems.
18 D.C. Reicosky and K.E. Saxton
Frye (1984) found fuel requirements using
reduced tillage or no-tillage systems were
55 and 78%, respectively, of those used
for conventional systems that included
mouldboard-ploughing. On an area basis,
savings of 23 kg/ha/year in energy carbon
resulted from the conversion of conventional
tillage to no-tillage. For the 186 million ha of
cropland in the USA, this translates to a
potential reduction in carbon emissions of
4.3 million metric tonnes carbon equivalent
(MMTCE)/year.
These results further support the energy
efficiencies and benefits of no-tillage. Conversion
of ploughed tillage to no-tillage,
using integrated nutrient management and
pest management practices, and enhancing
water use efficiency can save carbon emissions
and at the same time increase the soil
carbon pool. Thus, adopting conservation
agriculture techniques is a holistic approach
to management of soil and water resources.
Conservation agriculture improves efficiency
and enhances productivity per unit of
carbon-based energy consumed and is a
sustainable strategy.
Carbon Emissions and Sequestration
Tillage or soil preparation has been an integral
part of traditional agricultural production.
Tillage fragments the soil, triggers the
release of soil nutrients for crop growth,
kills weeds and modifies the circulation of
water and air within the soil. Intensive tillage
accelerates soil carbon loss and greenhouse
gas emissions, which have an impact
on environmental quality.
By minimizing soil tillage and its associated
(CO2) emissions, global increases of
atmospheric carbon dioxide can be reduced
while at the same time increasing soil carbon
deposits (sequestration) and enhancing
soil quality. The best soil management systems
involve minimal soil disturbance and
focus on residue management appropriate
to the geographical location, given the economic
and environmental considerations.
Experiments and field trials are required for
each region to develop proper knowledge
and methods for optimum application of
conservation agriculture.
Since CO2 is the final decomposition
product of SOM, intensive tillage,
particularly the mouldboard plough, releases
large amounts of CO2 as a result
of physical disruption and enhanced biological
oxidation (Reicosky et al., 1995).
With conservation tillage, crop residues are
left more naturally on the surface to protect
the soil and control the conversion of
plant carbon to SOM and humus. Intensive
tillage releases soil carbon to the atmosphere
as CO2, where it can combine with
other gases to contribute to the greenhouse
effect.
Soils store carbon for long periods of
time as stable organic matter. Natural systems
reach an equilibrium carbon level determined
by climate, soil texture and vegetation.
When native soils are disturbed by
agricultural tillage, fallow or residue burning,
large amounts of carbon are oxidized
and released as CO2 (Allmaras et al., 2000).
Duxbury et al. (1993) estimated that agriculture
has contributed 25% of the historical
human-made emissions of CO2 during the
past two centuries. However, a significant
portion of this carbon can be stored, or sequestered,
by soils managed with no-tillage
and other low-disturbance techniques. Increased
plant production greater than that
of native soil levels by the addition of
fertilizers or irrigation can enhance carbon
sequestration.
Carbon is a valuable environmental
natural resource throughout the world’s
industrial applications of production and
fossil energy consumption. Releasing carbon
to the atmosphere by energy processes may
be offset by capturing carbon with plant
biomass and subsequently soil carbon
sequestration in the form of organic matter.
Energy consumers may at some time be
required to compensate for their atmospheric
carbon emissions by contracting with those
who can sequester atmospheric carbon. Conservation
agriculture may be able to provide
this sequestration benefit and thus be compensated
for its role in maintaining low net
carbon emissions. While this ‘carbon trading’
mechanism is still in the discussion
Benefits of No-tillage 19
stage, it provides an important potential
benefit.
A more detailed explanation of carbon
dioxide emissions and sequestration is given
in Chapter 17, together with comments on
how these interact with nitrous oxide and
methane emissions and the potential for
carbon trading.
Summary of the Benefits of
No-tillage
Conservation tillage, and particularly
no-tillage, agriculture has universal appeal
because of numerous benefits. Improved
production with fewer inputs and reduced
time and energy are often cited as the highlights.
Conservation agriculture techniques
benefit the farmers and the whole of society,
and can be viewed as both ‘feeding and
greening the world’ for global sustainability.
Agricultural policies are needed to
encourage farmers to improve soil quality
by storing carbon as SOM, which will also
lead to enhanced air quality, water quality
and productivity and help to mitigate the
greenhouse effect.
Some of the more important benefits of
conservation tillage farming are:
1. Improved crop production economics.
2. Increased SOM.
3. Improved soil quality.
4. Reduced labour requirements.
5. Reduced machinery costs.
6. Reduced fossil-fuel inputs.
7. Less runoff and increased available
plant water.
8. Reduced soil erosion.
9. Increased available plant nutrients.
10. Improved global environment.
20 D.C. Reicosky and K.E. Saxton
3 The Nature of Risk in No-tillage
C. John Baker, W. (Bill) R. Ritchie and Keith E. Saxton
The ultimate decision to adopt a no-tillage
system will have more to do with how farmers
perceive it altering their business risks
than anything else.
The risks associated with no-tillage are those
that result in reduced income to the farmer
through impaired crop performance and/or
increased costs. To be a sustainable technique,
the failure rate for no-tillage must be
no more, and preferably less, than that for
tillage (Baker, 1995).
While early sceptics of the no-tillage
concept forecast many and varied problems
that would ultimately lead to the downfall
of the practice, experience has shown that
there are no insurmountable obstacles in
most circumstances. The fact remains, however,
that many farmers are still reluctant to
attempt the new technique, fearing that it
may increase their risks of crop failure or
reduced yield.
The perception of risk is probably the
single biggest factor governing the rate of
adoption of no-tillage, and it is likely to
remain so for a long time. Only education
and personal experiences will finally put
risk into perspective. Recent results convincingly
show that no-tillage is not inherently
more risky than conventional tillage,
even in the short term. Indeed, it can reduce
the risk factor during crop establishment
if it is undertaken and managed correctly.
Of course, tillage is also subject to increased
risk under poor management. It is therefore
pertinent to explore the concept of risk during
crop establishment and growth, and to
explain how this is affected by sound
no-tillage practices.
What is the Nature of Risk in
No-tillage?
To plant and grow a crop with no-tillage, a
farmer undertakes an economic risk that is
affected by three functional risk categories:
(i) biological; (ii) physical; and (iii) chemical.
These risks are comparable between
tillage and no-tillage systems because
almost all of them are the everyday risks
of cropping either way. Only their relative
levels and remedies differ between the two
techniques. The combined effects of the
functional risks result in economic risks.
The results and associated implications are
sometimes surprising and are examined at
the end of this chapter.
Biological risks
Biological risks arise from pests, toxins,
diseases, seed vigour, seedling vigour,
nutrient stress and, ultimately, crop yield.
© FAO and CAB International 2007. No-tillage Seeding in Conservation
Agriculture, 2nd edn. (eds C.J. Baker and K.E. Saxton) 21
The change to residue farming in general,
which is the cornerstone of no-tillage, can
have a marked effect on the incidence of
diseases and pests, both positively and negatively.
Seed placement and soil and residue
disturbance by various drill or opener
designs can influence all of these factors.
Pests
The change in earthworm and slug populations
creates the most common pest problems
in no-tillage. Slugs are particularly
prone to proliferate in residue in highhumidity
climates and must often be controlled
by chemical means. Earthworms, on
the other hand, can be either beneficial or
damaging, depending on type. Earthworms
generally provide positive effects that help
aerate, drain and cycle nutrients. All of the
effects of earthworms are not yet known but
some of their benefits in wet soils are
explained in detail in Chapter 7. While
tillage destroys earthworms, no-tilled soil
nearly always has a significant and important
increase in populations, and they are a
great ‘indicator’ organism for other beneficial
biota developments. Other damaging
worms, such as wireworms, are generally
not different regarding crop risks.
Slugs (Deroceras reticulatum) (Follas,
1981, 1982) find shelter beneath the soil in
many types of seed slots and feed on sown
seeds and establishing seedlings. Clearly,
slugs increase the biological risks of no-tillage.
But they are relatively cheaply countered by
the application of a suitable molluscicide.
Other pests can increase their damage
risk because of increased surface residues
or decreased physical destruction by tillage
machines. But then so too do many of their
predators.
An example of pest–drill interaction is
that experienced with inverted T-shaped
slots (see Chapter 4), which create subsurface
soil-slot environments that are
higher in soil humidity than either tilled
soils or other no-tillage slots. Soil fauna
that are sensitive to soil humidity, such as
slugs and earthworms, tend to congregate
in such slots. These may have both positive
and negative effects for the sown crop
(Carpenter et al., 1978; Chaudhry, 1985;
Baker et al., 1987; Basker et al., 1993).
Diseases
The most common soil disease that no-tillage
appears to encourage is Rhizoctonia. Disturbance
of the soil during tillage appears to
partly destroy the fungal mycelia. Other
fungal diseases are carried over in cereal
residue and decaying organic matter in root
channels, requiring diligent use of crop
rotations or application of appropriate
fungicides. On the other hand, the soil disease
take-all (Gaeumannomyces graminis)
appears to become more confined under
no-tillage because of reduced soil movement.
A concept called ‘green bridge’ was
identified by Cook and Veseth (1993), in
which certain root bacteria from recent
chemically killed plants can readily transfer
to new seedlings if no-tillage seeding is
undertaken within 14–21 days after the
green crop begins dying. The specific
pathogen has not yet been identified, but
some delay after spraying and before notillage
seeding appears to be an advantage
where these bacteria exist, particularly in
instances of continuous cereal cropping.
Toxins
The risks arising from toxins relate mainly
to contact between seeds and decaying residue
within the sown slot under persistently
wet conditions (see Chapter 7). This risk,
which is peculiar to no-tillage in cold wet
soils, is eliminated by the use of no-tillage
openers that effectively separate seed from
the residues (Chaudhry, 1985) or the use of
neutralizing agents sown with the seed
(Lynch, 1977, 1978; Lynch et al., 1980).
The most common occurrence of residue
effects has been experienced with doubledisc
drills seeding into wet, soft soils with
surface residues. The residues tend to be
folded and ‘tucked’ or ‘hairpinned’ into the
seed slot with the seed dropped in the same
location, which results in both the seed and
residue experiencing decaying conditions
and poor plant stands.
22 C.J. Baker et al.
Some explanations for early no-tillage
failures assumed that allelopathic exudates
from dying plants may have killed newly
sown seeds. But later detailed explanations
for the causes of seedling emergence failures
pointed to other (largely physical) factors
and it has been hard to find any
confirmed cases of allelopathy having played
any role at all.
Nutrient stress
Without soil tillage to stir and mix applied
fertilizer applications, careful attention
must be paid to placing the fertilizer in
untilled soils to optimize crop uptake and
yield. Bands of fertilizer to the side and
below the seed have proved to be very effective,
sometimes utilizing one fertilizer band
for each pair of seed rows. While it is
important to place fertilizers far enough
away from seeds and seedlings to avoid
toxicity problems (see ‘Chemical Risks’), it
also appears that separation distances can
(and indeed should) be much closer than
those commonly accepted for tilled soils
(see Chapter 9). Fertilizer banding has been
found to be optimally accomplished by
simultaneously seeding and fertilizing with
a combination direct seed drill and fertilizer
dispenser, and which is now common
practice.
Again, the risk under no-tillage increases
only if inappropriate equipment is used. On
the other hand, there is voluminous evidence
to show that, when fertilizers are
placed correctly, no-tillage crop yields may
be greater than those obtained from tilled
soils (see Chapter 9). Thus, while the risk of
nutrient stress under no-tillage may increase
with inappropriate equipment, it may
decrease compared with tillage if improved
designs of no-tillage drills and planters are
utilized.
Physiological stress
It has been stated that untilled seedbeds are
not as ‘forgiving’ as their tilled counterparts
(Baker, 1976a). This is often true because
seedlings have to emerge through covering
material that is physically more resistant
than friable tilled soils. If the seeds are sown
into mellow soils that have been no-tilled
for several years or with scientifically
designed furrow openers, such as inverted-
T-shaped slots, the micro-environment of
the slots will actually place less physiological
stress on the seedlings than will a tilled
soil. Thus physiological stress at the time of
seedling emergence need not increase the
biological risks. It may actually decrease
the risk (see Chapter 5). Figure 3.1 shows
the difference in growth between seedlings
established within contrasting no-tillage
slots resulting from physiological stress.
Seed quality
International seed testing authorities
throughout the world test mainly for purity
and optimally wetted germination as the
main indicators of seed quality. But there
are also agreed voluntary tests that describe
other aspects of seed quality. One such test,
the ‘accelerated ageing’ or ‘vigour’ test,
examines a seed’s ability to germinate after
experiencing a period of stress (usually
high or low temperature). It is possible for a
given seed line to record a high-percentage
germination but a low-percentage vigour.
Therefore final germinations counts give no
real indication of the vigour of a seed line
although interim counts might be helpful in
this respect.
There is an important interaction between
seed vigour and drill opener designs, which
can have important impacts on biological
risk, and operators need to understand this
interaction. No-tillage openers that create
inverted-T-shaped slots produce about as
favourable a micro-environment as it is
possible to create for seeds, in either tilled
or untilled soils. The main attribute is the
availability of both vapour-phase and
liquid-phase water. This ensures that even
low-vigour seeds will germinate, almost
regardless of the soil conditions.
In contrast, seeds sown into tilled soils
or less favourable no-tillage slots that only
provide liquid-phase water for germination
of seeds are less likely to germinate. Farmers
usually attribute such failures to a variety
of reasons, but seldom test the vigour of
Risk in No-tillage 23
the seed they had sown. When germination
of low-vigour seeds does occur in tilled
soils and open no-tillage slots, emergence of
the seedlings is seldom restricted because
of the friable nature of tilled soils and the
open nature of vertical no-tillage slots. But
the ensuing crop is likely to perform poorly.
Extensive field experience with
inverted-T-shaped no-tillage slots, where
even low-vigour seeds will often germinate
under unfavourable conditions, have shown
that the seedlings often did not have the
vigour to emerge and were instead found
twisted, weak and un-emerged beneath the
soil surface. Observers at first attributed
such twisting to fertilizer burn, but it is now
known that fertilizer burn causes shrivelling
and premature death of seedlings, not
twisting. When vigour tests were carried
out over a 3-year period on some 40 lines of
seeds that had shown symptoms of subsurface
seedling twisting in inverted-T
no-tillage slots, all seed lines were found to
be of low vigour (some as low as 18%).
The question is: What can be done
about the problem? The responsibility rests
with both the seed industry and individual
no-tillage farmers. The seed industry needs
to improve the quality of the seeds it offers
for sale or at least be prepared to disclose
information on seed vigour to farmers. Some
companies already do this. No-tillage farmers,
for their part, need to seek information
from the seed industry about the vigour
of particular seed lines and to be prepared
to pay more for high-vigour lines. Those drill
manufacturers that market advanced notillage
seed drills need to advise purchasers
that the weakest part of the system may now
be seed quality, whereas previously it had
been drill quality.
Physical risks
Weather
Weather is likely to be the most variable
and uncontrollable element in farming, and
performing no-tillage won’t change that.
However, no-tillage does have the opportunity
to significantly modify the impact by
several means, some already mentioned or
obvious. Increased available plant water is
often the first noticeable effect, since residues
and minimal soil disturbance reduce
evaporation and increase infiltration.
Improved trafficability in wet soil is
often a surprising no-tillage effect. With only
24 C.J. Baker et al.
Fig. 3.1. Growth responses of wheat seedlings as a result of physiological stress when sown by a
winged opener (left) and double disc (right) no-tillage openers.
one or two no-tillage crop years, the ‘fabric’
of the soil strengthens (mainly through
improved soil structure) and animal or
machine treading causes much less compaction
with fewer surface depressions. It is
common knowledge that no-tilled fields are
accessible for seeding or spraying several
days sooner following rainfall than tilled
soils, with less damage by surface compaction.
No-tilled soils are not more dense or
compact than tilled soils; they just have
more resistance to down pressures as a
result of the increased organic matter and
structure.
No-tillage also moderates excessive
weather effects, such as extreme rainfalls and
temperatures. With the surface residues protecting
the surface against raindrop impact,
runoff and erosion, rills and gullies don’t
form. Residues minimize the high wind profiles
from having an impact on the soil surface
and significantly reduce wind erosion.
And very subtle dampening of soil temperature
variations often prevents freezing of
overwintering plants. No-tillage seeding into
standing residues has allowed successful
winter wheat crops in far more northerly
climates in the northern hemisphere than
previously possible, with increased yields
compared with spring-seeded crops.
Young et al. (1994) showed how seasonal
weather variations could affect the
risk of altering the profitability of conservation
tillage (which includes a component of
no-tillage) compared with conventional tillage
(Fig. 3.2). They pointed out that the
period 1986 to 1988 was particularly dry in
the Palouse area of Washington State, which
favoured the profitability of conservation
tillage. The 1990/91 winter was particularly
cold, which also favoured conservation tillage.
At other times (1989 and 1990) the
weather did not favour either technique. In
this manner the relative risks of changing
profitability are clearly illustrated. Such
risks cannot be predicted with any accuracy,
but they can be minimized by selecting
conservation tillage techniques and/or
machines with the widest possible tolerance
of changing weather patterns.
It is obvious that no-tillage machines
cannot control the weather. But it has been
repeatedly noted that when no-tillage is
undertaken with appropriate residue manipulation
and seeding machines designed
with proper seeding slots, seeds and seedlings
have considerably better protection
from weather variations (e.g. too hot, cold,
dry, windy or wet) than when that soil is
either tilled or drilled with inappropriate
Risk in No-tillage 25
Fig. 3.2. The relative profitability of two crop establishment systems in Washington State over 5 years
(from Young et al., 1994).
no-tillage equipment. Thus, risks arising
from inclement weather have the potential
to be reduced under no-tillage if appropriate
methods and equipment are used.
Machine function
Many of the physical risks arise from how
well no-tillage machines perform their
intended functions. The machine's designers
must understand and incorporate the
required capabilities to perform its intended
functions in a wide variety of soil types, residues
and weather conditions. These variations
can change widely even within a single
field or on a single day. There is much risk
inserted into the farming system from a
machine that operates at different levels of
performance on different days in different
parts of a field. A successful no-tillage drill
must have a wide tolerance of changing,
sometimes even hostile, conditions.
There are few more important physical
functions than creating the correct microenvironment
for the seeds within the soil.
Different drill openers differ markedly in
their abilities to do this (see Chapter 4) and
this affects the level of risk associated with
different machines. To reduce machinerelated
risks, the openers of no-tillage drills
must follow ground surface variations and
move through significant surface residues
without blockage. Seeding depth can only
be maintained by careful tracking of the soil
surface by the seed opener.
Maintaining surface residues is the
main long-term benefit from no-tillage,
especially for reducing erosion and temperature
fluctuations and increasing soil fauna
and infiltration. Residues are an equally
important ingredient in short-term biological
performance of seedling emergence
and vigour. No-tillage does not offer the
option to ‘till out’ last season’s mistakes of
vehicle ruts, animal paths, washed gullies,
hardpans, etc. It is critically important to
avoid creating field surfaces that are not
mechanically manageable the following
cropping season.
No-tillage seeding machines not only
must physically handle residues consistently
without blockage but must also have
the ability to micro-manage those residues
close to the slot and to utilize them for the
benefit of the sown seeds and plants (Baker
and Choudhary, 1988). Conversely, the
inability of any opener to do these things
significantly increases the risks from notillage,
since the residues themselves are an
important ingredient in creating a favourable
habitat for seeds and seedlings. A positive
utilization of crop residues in no-tillage
is considerably different from tillage farming
in that residues are seen as beneficial
rather than a hindrance to machine performance.
Since tilled soils, almost by definition,
have minimal surface residues, they
do not benefit in comparison with good
utilization of residues by no-tillage openers,
but they may compare well with no-tillage
where residues are not utilized.
Similarly, the ability to uniformly track
the untilled soil surface for uniform seeding
by no-tillage drills will greatly determine
the biological risks associated with poor
seedling stands and vigour. These aspects
are discussed in greater detail in Chapter 8,
but in summary it should be acknowledged
that there is a need for no-tillage openers to
follow the surface better than their tillage
counterparts, or the risk of poor crop stands
will increase.
No-tillage drills encounter much higher
forces and wear of components than their
tillage counterparts. Since some of the critical
functions, such as residue handling and
slot formation, are often dependent on the
mechanical wear remaining within narrow
limits, maintenance of no-tillage machines
is more important than for conventional
drills. To put it another way, the absence
of adequate maintenance on no-tillage
drills may increase the risk of malfunction
disproportionately.
None of the physical functions described
above, however, has any relevance to risk
unless its successful implementation has an
identifiable biological function with regard
to the sown seeds and emerging plants.
Somewhat surprisingly, many of the early
‘desirable functions’ listed for no-tillage
openers (e.g. Karonka, 1973) failed to define
any biological objectives at all. Failure
to recognize these biological-engineering
26 C.J. Baker et al.
linkages alone probably increased the level
of risk of early no-tillage and accounted for
much of the ‘hit-and-miss’ reputation the
technique acquired in its early days.
Ritchie et al. (2000) summarized the
biological risks associated with six critical
functions that no-tillage drill openers must
perform. Their modified chart is shown in
Fig. 3.3. Each criterion was assigned a risk
rating of 1 to 10 (1 being low-risk and 10
being high-risk) according to published
scientific data and engineering principles.
Several commonly used drill openers
were ranked using the criteria of Fig. 3.3 and
are shown in Table 3.1. The risk-assessment
of the disc version of winged openers closely
matches actual field surveys of users in
New Zealand, which have consistently found
a 90–95% success rate over several years
and hundreds of thousands of hectares of
field drilling (Baker et al., 2001). But the
most commonly used opener throughout the
world (vertical double disc) ranks poorly.
This helps explain the many no-tillage
failures associated with this opener.
Chemical risks
Chemical risks have many of the same
implications as physical risks. They are
linked to the resultant biological risks that
arise from them. Two stand-alone chemical
risks are the effectiveness of weed control
by herbicide application and the risk of
toxicity or ‘seed burn’ from inappropriate
placement of fertilizer in the seed slot relative
to the seed placement.
Weed control
Weed control with herbicides must be as
effective as that with mechanical means or
the risk of impaired crop performance will
increase. The principal variables determining
herbicide effectiveness are as follows.
APPLICATION OF ACTIVE INGREDIENT. The ability
of operators to properly interpret the labels
and literature supplied with various herbicides
and pesticides has much to do with
the success of applications. In addition,
operators need to be able to recognize weed
species and to be able to reliably calibrate
their spraying machines. All of these operator
choices are more risky than corresponding
tillage operations. Nor are spraying
mistakes as forgiving as tillage mistakes,
which can often be ‘repaired’ the next day.
SELECTION OF APPROPRIATE CHEMICAL. The
selection of tillage tools can follow a trialand-
error routine where: (i) the nonperformance
of one implement becomes
obvious within a short time; (ii) the consequences
are seldom of great magnitude; and
(iii) rectification using an alternative implement
is accomplished quickly. Few, if any,
of these flexibilities are available when
choosing appropriate chemicals for a given
weed or pest situation. Occasionally a mistaken
choice can be rectified by the application
of another chemical, but the options
are fewer than with tillage and the risks are
therefore greater.
WEATHER. Some chemicals require several
hours without rain to be fully effective,
while others are virtually ‘rain-fast’. Since
most chemicals involve a significant outlay
of cash and, unlike tillage tools, are not
reusable, the risk from untimely rain and
wind is greater than with tillage.
WATER QUALITY. Some foliage-applied herbicides,
especially those that are inactivated
upon contact with soil, such as glyphosate,
have their efficacy altered by impurities in
the mixing water. Of particular concern is
water derived from storage dams or underground
bores that is contaminated with particles
or iron and carbonates. Some chemical
effectiveness is quite variable with water
acidity levels. Similarly, impurities on the
leaves of target foliage, such as mud and
dust from stock or vehicle traffic or recently
applied lime, may inactivate some herbicides.
VIGOUR OF WEEDS. The vigour of the target
weeds at application time is important.
Some herbicides (e.g. glyphosate) work best
when sprayed on to healthy, actively growing
plants. Others (e.g. paraquat) work best
Risk in No-tillage 27
28 C.J. Baker et al.
Fig. 3.3. A biological risk-assessment chart of drill opener designs (after Ritchie et al., 2000).
when the target plants are already stressed.
Knowledge of these requirements is essential
if effective weed control is to take place.
OPERATOR ERROR. During tillage, driving
errors by an operator are seen immediately
but they are seldom sufficiently serious to
show up in the subsequent crop as an area
of impaired yield. With once-over spraying,
errors do not show up immediately.
Paraquat is the most rapid to take effect but
even then it is days before mistakes become
visible. Most other herbicides take at least a
week to show any visible effect, by which
time the crop may have been sown, making
remedial action virtually impossible without
adversely affecting the sown crop.
Toxicity of fertilizers
There are two risks from inappropriate fertilizer
placement at sowing. If fertilizer is
broadcast on to the ground surface rather
than placed in the soil at the time of drilling,
there is a serious risk of impaired crop
performance and yield as a result of limited
plant availability (see Chapter 9). On the
other hand, when fertilizer is sown with the
seed there is a danger of the fertilizer damaging
or ‘burning’ the seed under no-tillage
unless the two are effectively separated
in the soil. The latter risk increases with
increased soil dryness. Separation is more
difficult to achieve in no-tillage than in
tilled soils, but it has been shown to be
quite possible with the correct equipment
without increased risk.
Economic risk
All forms of risk during no-tillage are finally
measured as economic risk. But economic
Risk in No-tillage 29
Disc version
of winged
opener
Vertical
angled
disc
Slanted
angled disc
Shank and
sweep
openers
Vertical
double disc
Simple
winged
tinea
Slot microenvironment
1 4 4 3 7 2
Slot covering 1 3 2 2 7 4
Fertilizer
placement
1 3 3 2 7 7
Seed depth
control
2 1 1 9 3 8
Surface following 1 4 4 9 5 9
Residue handling 1 3 3 7 3 10
Total out of
max. 60
7 18 17 32 32 40
Chance of
impaired biological
performanceb
11% 30% 28% 53% 53% 67%
aSimple winged tine openers are designed to be used predominantly in smooth pasture. Comparing
these openers for all no-tillage (including arable) penalizes them unfairly but they are nevertheless
included here to illustrate how Fig. 3.3 exposes the limitations of such openers.
bThe figures represent the chances of obtaining an impaired biological performance from using any of
these openers. For example, the table suggests that use of the disc version of winged openers will result
in an 11% chance of a poor crop, whereas use of shank and sweep openers will result in a 53% chance
of a poor crop unless there is little residue present and the fields are smooth and flat.
Put another way, the table suggests that in heavy residues on less-than-smooth ground there would be
about five times as much chance of getting an impaired crop using shank and sweep type openers as
compared with the disc version of winged openers.
Table 3.1. Examples of how some common no-tillage openers rank in terms of biological risk.
risk should not be centred on cost savings
alone. Indeed, focusing on cost savings may
increase rather than decrease both real and
imagined economic risks. This is for two
reasons:
1. Where farmers already own tillage
equipment, they see the acquisition of
no-tillage equipment or even the use of contractors
(custom drillers) – no matter how
cheap – as duplication of an existing cost.
2. Purchasing inferior no-tillage equipment
for cost savings may well result in lowered
crop yields, even if only temporarily. Such
a result may indeed be less cost-effective
than either tillage or no-tillage undertaken
with more expensive (and probably superior)
equipment that maintains or even
improves crop yields.
We shall examine both scenarios below.
The costs of tillage versus no-tillage
The costs of several alternatives for adopting
no-tillage under a double cropping system
(two crops per year, e.g. wheat followed
by a winter forage crop for animal consumption)
in New Zealand were analysed
and compared with the costs of tillage
(C.J. Baker, 2001, unpublished data).
These were:
1. Engaging a tillage contractor (custom
driller) versus engaging a no-tillage contractor.
2. Purchasing new tillage equipment versus
purchasing new no-tillage equipment.
3. Retaining ownership of used tillage
equipment versus purchasing used no-tillage
equipment.
4. Retaining ownership of used tillage
equipment versus purchasing new no-tillage
equipment.
5. Retaining ownership of used tillage
equipment versus engaging a no-tillage
contractor.
Fixed costs were included, such as
interest on the investment, depreciation,
insurance and housing, and expressed as a
per-hour cost of annual machine use. Drills
and planters are used for a shorter period
each year to plant the same area under notillage
than under a tillage regime. Thus the
per-hour costs increase even though the
per-hectare and per-year costs decrease.
The analysis also assumed that a single
large tractor and driver would be required
for no-tillage compared with two or more
smaller tractors and drivers for tillage.
For simplicity, the study assumed that
the no-tillage drill being compared was of
an advanced design, which ensured that crop
yields would remain unchanged regardless
of which option was chosen. Such an
assumption is reasonable when applied to
advanced no-tillage drills (which cost more
anyway) but is unrealistic for inferior drills
(see below).
The cost analysis did not account for
taxation issues, subsidies or other purchase
incentives of any nature. These could otherwise
be expected to favour no-tillage since
many countries have incentives to encourage
the practice because of its conservation
value. Thus the results could be considered
conservative in terms of the benefits
recorded for no-tillage.
A more detailed account of the economic
analysis is given in Chapter 18.
Operating costs strongly favoured notillage.
In all of the above options (1) to (5),
the costs favoured no-tillage by between
US$16 and US$40/ha/year.
The greatest advantage (US$40/ha/year)
was shown by option (2) – purchasing new
tillage equipment versus purchasing new
no-tillage equipment. This was mainly
because of reduced running costs of the
no-tillage equipment since the total capital
outlays in each case were very similar.
The least advantage (US$16/ha/year)
was shown by option (4) – retaining ownership
of used tillage equipment versus purchasing
new no-tillage equipment. Clearly
the advantage would increase for this
option when and if a decision was eventually
taken to sell the existing tillage
equipment, provided that a market for such
equipment still existed. But realistically,
the costs of purchasing no-tillage equipment
would probably remain additional to
the costs of retaining ownership of existing
tillage equipment for a period.
Farmers often see retention of their
existing tillage equipment as ‘insurance’
30 C.J. Baker et al.
while they gain the knowledge and skills
necessary to master the new no-tillage technique
to a stage where they can abandon
tillage altogether. Other farmers claim that
by going ‘cold turkey’ (i.e. selling the tillage
equipment at the same time as they purchase
the no-tillage equipment) the learning
process is achieved faster and more effectively.
This study took the conservative
approach.
The advantage for no-tillage from
option 1 – engaging a no-tillage versus tillage
contractor – was US$36/ha/year. The
advantage for no-tillage from option 3 –
retaining ownership of used tillage equipment
versus purchasing used no-tillage
equipment – was US$30/ha/year and for
option 5 – retaining ownership of used tillage
equipment versus engaging a no-tillage
contractor – was US$34/ha/year. Cost
advantages for no-tillage would be expected
to increase when sale of the existing tillage
equipment became feasible.
Machine impacts on crop yields and
economic risk
The effect of any one no-tillage drill design
on crop yield and risk (and therefore economic
returns) will be more important than
its initial cost, when compared with either
tillage or cheaper no-tillage alternatives.
This belief has caused the research and
development of improved no-tillage machines
and systems as a means to reduce the risks
associated with the practice, almost regardless
of cost. The following analyses of
machine capability versus expected crop
yields and the resulting economics clarifies
this belief.
The per-hectare charges that no-tillage
contractors (custom drillers) make for their
services are a good barometer of the relative
costs associated with different no-tillage
machines and systems. If we take New
Zealand contractors as an example, we
find that those with advanced (expensive)
no-tillage drills in 2004 charged between
US$72 and US$96/ha for their services,
whereas those with lesser (cheaper) drills
charged between US$36 and US$60/ha.
Differences between the ranges of
charges are attributable mainly to differences
in the initial costs of the two classes
of machines and the different sizes of tractors
needed to operate them. Differences
within both ranges of costs reflect differences
in the costs of competing options
(such as tillage) together with differences
in work rates and maintenance costs
brought about by different field sizes,
shapes, topographies and soil types (including
abrasiveness).
Taking the midpoint of each scale,
the premium a farmer therefore paid in
New Zealand in 2004 for access to a more
advanced drill was about US$36/ha. Actual
contractor charges in other countries will
differ from these figures but the relativity
between the costs associated with advanced
machines and lesser machines is likely to
be similar.
So a key question is: How much does
an advanced no-tillage drill have to
increase crop yields in order to justify the
US$36/ha premium paid for the better technology
under 2004 price conditions?
Wheat sold in New Zealand in 2004 for
approximately US$170/t. The average yield
of spring-sown wheat in New Zealand in
2004 was 5.7 t/ha and the average autumnsown
wheat yield was 7.4 t/ha (N. Pyke,
Foundation for Arable Research, 2004, personal
communication). Gross returns for
average spring- and autumn-sown wheat
crops in 2004 were therefore US$969/ha
and US$1258/ha, respectively.
To recover an additional US$36/ha in
the costs of no-tillage drilling would require
an increase in yield of 0.21 t/ha (or
210 kg/ha). This represented a 3.7% increase
in yield of a spring-sown wheat crop or a
2.9% increase in an autumn-sown wheat crop.
Such yield increases have been common.
For example, the US Department of
Agriculture obtained an average of 13% wheat
yield increase in seven separate experiments
over a 3-year period in Washington
State by switching to a more advanced notillage
drill compared with the best ‘other’
no-tillage drill that was then available
(Saxton and Baker, 1990). Similarly, the
New South Wales Department of Agriculture
Risk in No-tillage 31
(Australia) recorded an 11-year average of
27% yield advantage from soybean sown
annually after oats using the same advanced
no-tillage openers, compared with tillage
(Grabski et al., 1995).
Commercial field experience over a
9-year period in New Zealand, the USA and
Australia suggests that such research-plot
measurements have been a realistic reflection
of field expectations. Wheat and other
crop yields approaching twice the national
averages have become common from notillage
practised at its most advanced level.
Conclusions
It can be said that, when comparing the
economic risks of tillage and no-tillage,
more management and more sophisticated
machinery are needed to undertake notillage
correctly and successfully. But, if the
appropriate management and machinery
are used and the reasons for these choices
are understood, there will be no more and
often less economic risk with no-tillage
than with tillage. All of the various forms
of risk come together in the multiple-year
rotations required of modern farming in an
integrated management system. Figure 3.4
illustrates the results of a comprehensive
assessment of financial risk made during 6
consecutive years of experiments by Young
et al. (1994) in Washington State, USA.
These experiments compared the combined
results of conservation tillage, which
included several consecutive years of
no-tillage, versus conventional tillage, the
effects of maximum, moderate and minimum
weed control and crop rotations, all
under a high level of agronomic management.
Considering all treatments and 6
years of variable weather factors, conservation
tillage had the smallest economic risk
due to conserved moisture, good yields and
low inputs. They concluded that the winter
wheat–spring barley–spring peas rotation at
maximum or moderate weed management
32 C.J. Baker et al.
Fig. 3.4. Profit and risk analyses for 12 cropping systems in the Palouse area, Washington, 1986–1991
(from Young et al., 1994). WWW, wheat, wheat, wheat rotation; WBP, wheat, barley, peas rotation.
levels (RM3 or RM2) dominated all other
systems in profitability (profit of $30–40/ha)
and had the lowest economic risk or ‘profit
variability’.
Summary of the Nature of Risk in
No-tillage
1. The perception that no-tillage involves
greater risk than tillage is one of the greatest
impediments to its more widespread
adoption.
2. The combination of all the components
of risk manifests them as economic risk.
3. The components of risks in no-tillage
are biological, physical and chemical.
4. Biological risks relate to pests, toxins,
nutrient stress, seed vigour, seedling vigour,
disease and impaired crop yield.
5. Physical risks relate to weather, slot
micro-environment and machine performance
and reliability.
6. Chemical risks relate to the supply and
availability of plant nutrients, seed ‘burn’
from fertilizers and the effectiveness of
application of chemical herbicides and
pesticides.
7. The function and design of no-tillage
seed drills can have an influence on pests,
toxins, nutrient stress, diseases, fertilizer
‘burn’, slot micro-environment, machine
performance and durability and the supply
and availability of plant nutrients.
8. Performed correctly with appropriate
equipment, no-tillage has no more, and
often less, total risk than tillage, even in the
short term.
9. Performed incorrectly with inappropriate
equipment, no-tillage has greater
associated risk than tillage.
10. It is often ‘false economy’ to cut costs in
no-tillage, particularly in machine effectiveness,
as the savings in cost may be much
less than the reductions in crop yield that
are likely to result.
Risk in No-tillage 33
4 Seeding Openers and Slot Shape
C. John Baker
Very few no-tillage openers were originally
designed for untilled soils. Most are adaptations
of conventional openers for tilled soils.
A seeding opener is the soil-engaging
machine component that creates a ‘slot’,
‘furrow’ or ‘opening’ in the soil into which
seed and perhaps fertilizer and insecticide
are placed. Different shapes of soil slots may
be created by conventional and no-tillage
openers. The most important feature is the
cross-sectional shape, as if you had cut
across the opener path after its passage with
a knife and were looking at the vertical
exposed face.
Openers are the only components of a
no-tillage drill or planter that actually break
the soil surface. In no-tillage seeding, they
are required to perform all of the functions
necessary to physically prepare a seedbed
as well as sow the seed and perhaps fertilizer.
In contrast, in conventional tillage a
succession of separate tillage tools are used
to prepare the seedbed, and the seed drill
then only has the relatively simple task of
implanting the seed and perhaps fertilizer
into a pre-prepared medium.
A large amount of scientific evidence
shows that the most important aspect of
the mechanics of different no-tillage opener
designs is the shape of the slots they create
in the soil and their interaction with seed
placement and seedling emergence and
growth. Generally, there are three basic slot
shapes created by no-tillage openers and
two other ways of sowing seed that do not
involve creating a continuous soil slot at
all: (i) V-shaped slots; (ii) U-shaped slots;
(iii) inverted-T-shaped slots; (iv) punch
planting (making discrete holes in the
ground and sowing one or more seeds per
hole); and (v) surface broadcasting (seeds
randomly scattered). Only one slot shape,
the inverted-T slot, is used in no-tillage that
has not been an adaptation of a slot shape
already used for tilled soils.
Figure 4.1 is a diagrammatic representation
of slot shapes i–iii as created in a silt
loam soil at three different moisture contents
(Dixon, 1972). The mechanics of each
of these seeding methods and the resulting
characteristics will be further discussed in
detail in the following sections.
Several authors (e.g. Morrison et al.,
1988; Bligh, 1991) have compiled lists and
diagrams of openers and in some cases
compared observations of field performance.
But few detailed scientific studies
have been made in which all but the
important variables being studied have
been controlled or accurately monitored.
Such studies (which also included some
new and innovative designs) are reported
below.
© FAO and CAB International 2007. No-tillage Seeding and Conservation
34 Agriculture, 2nd edn. (eds C.J. Baker and K.E. Saxton)
Vertical Slots
V-shaped slots
In untilled soils, V-shaped slots are almost
invariably created by two discs that touch
(either at their bases or behind this position)
and are angled outwards towards their
tops. The two discs are not always of equal
diameter. The included angle (the angle of
the V) is usually about 10°, but this is not
critical. Seed is delivered into the gap
between the two discs, preferably rearwards
of the centre ‘pinch point’, so as to prevent
the seed from being crushed as the discs
come together.
When arranged so that both discs are
at the same angle to the vertical, the slot
has a vertical V shape and is created by
each of the angled discs pushing roughly
equal amounts of soil sideways. The
front edges of the two discs at the groundsurface
level are apart from one another,
which can cause a problem if residues
enter the gap. To avoid this they are usually
configured in one of the following
three forms.
Double disc: offset (Fig. 4.2)
In this form one of the two angled discs
(there is no third leading disc) is positioned
forward of the other so as to present a single
leading cutting edge and deflect residue.
The second disc still forms the other side of
a vertical V but its leading edge is nestled
behind that of the first disc, thus avoiding
residue blockage and reducing the magnitude
of downforce required for penetration.
Double disc: unequal size (Fig. 4.3)
By placing the smaller of the two discs
alongside its larger neighbour, the leading
edge of the larger disc becomes the leading
edge of the whole assembly in much the
Seeding Openers and Slot Shape 35
Fig. 4.1. Typical profiles of
vertical V- (left), U- (centre)
and inverted-T- (right) shaped
no-tillage seed slots in a silt
loam soil at 15%, 20% and
27% moisture contents (from
Dixon, 1972).
36 C.J. Baker
Fig. 4.2. Typical offset double disc no-tillage openers that create vertical V-shaped slots.
Fig. 4.3. Typical unequal-sized double disc no-tillage openers that create vertical V-shaped slots.
same way as for the offset design. Often, the
smaller disc is also offset.
Triple disc (Fig. 4.4)
In this form a third vertical disc is placed
ahead of, or between, the two angled discs.
This additional disc cuts the residue sufficiently
for the two following discs to deflect
it sideways. The third disc, however, adds
to the amount of downforce required for
penetration.
All forms of double disc and triple
disc openers create vertical V-shaped slots
since the actual slot shape is created by the
two angled discs, regardless of their sizes
or offsets. The third (leading) disc in the
triple disc configuration mainly cuts the
residue and influences the slot in a minor
way. The triple disc design with the leading
disc operating slightly below the bases
of the two angled discs reduces some of the
detrimental effects of ‘hairpinning’ (see
Chapter 7, ‘Drilling into Wet Soils’) and
root penetration problems common to both
double and triple disc configurations. Similarly,
by using a wavy-edged leading disc
(sometimes referred to as a ‘turbo disc’), a
degree of soil loosening will usually be
achieved ahead of the two angled discs and
this helps offset the compacting tendencies
of the following double discs.
The action of vertical double disc openers
in the soil is to wedge the soil sideways
and downwards in a V formation. They do
not normally heave or raise the soil upwards.
In some very sticky soils that cling to the
outsides of the discs, some of that soil will
be torn away and carried upwards, leaving a
disrupted slot (Fig. 4.5).
Figure 4.6 shows the zones of compaction
created by a vertical triple disc opener
operating in a normal manner in a silt-loam
soil (Mitchell, 1983).
From a dry soil perspective, the most
distinguishing feature of the slot is the neatness
of the vertical V-shaped cut, unless the
soil is friable, in which case this neat cut
may collapse. But even friable soils progressively
become more structured and less friable
(as organic matter levels and microbial
action increase under no-tillage). Thus, with
time, most vertical V-shaped slots become
more clearly defined and less likely to
collapse of their own accord after passage of
the opener.
Seeding Openers and Slot Shape 37
Fig. 4.4. A typical triple disc no-tillage opener that forms a V-shaped slot (from Baker, 1976b).
Because of its wedging action, there is
often little or no covering material available
to cover seeds placed into the bottom of the
V slot. This is even more of a problem when
the opener is used in a moist, non-friable
soil. Figure 5.1 illustrates such a situation.
The plastic nature of the moist soil prevents
the formation of loose soil crumbs, which
38 C.J. Baker
Fig. 4.5. A slot created by a vertical double disc opener in wet sticky soil in which the soil has stuck to
the outside of the disc and been pulled up from the slot zone.
Fig. 4.6. The pattern of soil strength around a vertical V-shaped no-tillage slot as created by a triple
disc opener in a damp silt loam soil (from Baker et al., 1996).
might otherwise fall back over the seed as
covering material (see Chapter 5).
The usual recourse is to follow vertical
double disc openers with some configuration
of V-shaped press wheels arranged so
that they squeeze the soil in the opposite
direction to the discs after the seed has been
deposited (Fig. 4.7). Unfortunately, this
action is also one of compaction, albeit in
the opposite direction to the original forces.
In an untilled soil, the wedging action of
vertical double disc openers does little, if
anything, to create a favourable environment
for seeds.
The greatest advantages of vertical double
disc openers are: (i) their construction is
relatively simple and maintenance-free,
although the latter attribute depends on the
use of good bearings and seals; and (ii) their
ability to pass through surface residues
without blockage.
The most important disadvantages
are: (i) the high penetration forces required;
(ii) their poor performance in suboptimal
soil conditions; (iii) their tendency to tuck
(or ‘hairpin’) residue into the slot, which in
dry soils interferes with seed–soil contact
and in wet soils results in fatty acid
fermentation that kills germinating seeds
(Lynch, 1977); and (iv) the inability of individual
openers to separate seed from fertilizer
in the slot. Indeed, due to the shape of
the slot, vertical double disc openers tend
to concentrate the seed and fertilizer
together at the base of the slot more than
other openers (Baker and Saxton, 1988;
Baker, 1993a, b).
Despite these shortcomings, vertical
double disc openers have been included on
more no-tillage drill designs than any
other opener design to date. Unfortunately,
however, because of their dependence on
favourable soil conditions to achieve acceptable
seeding results (or, more correctly,
their intolerance of unfavourable conditions),
they have also been responsible for
much of the perception that risk increases
with the practice of no-tillage.
It is important to emphasize the distinction
between tilled and untilled soils
and to illustrate the dangers inherent in
deriving designs of no-tillage machines
from those that had been successful in tilled
soils. Tilled soils are naturally soft before
seeding and the wedging action of vertical
double disc openers is generally beneficial,
Seeding Openers and Slot Shape 39
Fig. 4.7. Press wheels arranged in a V configuration for closing no-tillage slots created by vertical
double disc openers (from Baker, 1981a, b).
especially when the soil is dry. It consolidates
the soil alongside and beneath the
seed, which results in increased capillary
movement of water to the seed zone. Covering
is seldom a problem in tilled soils,
because the entire seedbed is comprised
of loosened soil. Thus, in many ways,
V-shaped openers are an advantage in tilled
soils, whereas they have serious shortcomings
in untilled soils.
Other mechanical forms of vertical
V-shaped openers for tilled soils simply do
not work in untilled soils because they will
not penetrate in the less friable conditions.
These include sliding shoe-type openers
and V-ring roller openers (Baker, 1969b).
Further consideration of these designs is
not justified since they simply cannot effectively
seed no-tilled soils.
Slanted V-shaped slots
To reduce the compaction tendencies of
vertical V-shaped slots, some designers
have slanted double or triple disc openers
at an angle to the vertical, and sometimes
also angled to the direction of travel. When
they are slanted vertically, the uppermost
disc pushes the soil partially upwards, thus
reducing the compaction that otherwise
results from the soil being displaced only
sideways by vertical double disc openers.
The lowermost disc on slanted double disc
openers, however, is then forced to displace
soil in a more downward direction, adding
to its compaction tendency. Since roots
mainly travel in a downward direction, it is
debatable whether or not the slanting of
double or triple disc openers overcomes the
disadvantages inherent from their tendency
to compact the slot in the root zone. On the
other hand, slanting of V-shaped slots
undoubtedly makes them easier to cover,
since a near-vertical press wheel is required
to shift soil more in a downward direction
than sideways.
Two slanting double discs can be combined
in such a way that the front pair of
discs (which are angled vertically in one
direction) sow fertilizer and the rear pair of
discs (which are angled vertically in the
opposite direction) sow seed at a shallower
depth. Not only does this effectively
separate seed and fertilizer in the vertical
plane, but additionally the zone that would
normally be compacted below the seed by
the lowermost disc of the rear opener is
pre-loosened by the uppermost disc of the
front opener, thus partly negating the undesirable
compaction effect of the seeding
opener. Figure 4.8 shows a pair of slanted
double disc openers.
Single discs that are angled in relation
to the direction of travel (and sometimes
also slanted vertically) are discussed below.
U-shaped slots
There is a wide range of opener designs that
form U-shaped slots (Baker, 1981a, b):
(i) angled disc-type openers; (ii) hoe openers;
(iii) power till openers; and (iv) furrowers.
The slots made by all of these designs
are distinguishable from V-shaped slots by
the slot bases being broad rather than
pointed like a V. The slot-making action of
40 C.J. Baker
Fig. 4.8. A pair of slanted discs at opposing
angles. The front discs place fertilizer and the rear
discs place seed at a shallower depth. (From
Baker et al., 1996.)
each of these openers is quite different,
even though they all result in a similarly
shaped slot, but none of the openers has the
downward wedging action of double disc
openers. Thus there is less soil compaction
associated with all U-shaped slots than
with V-shaped slots.
Angled disc-type openers mostly scrape
soil away from the centre of the slot; hoeand
furrow-type openers burst the soil
upwards and outwards; power till openers
chop the soil with a set of rotating blades;
and furrow-type openers scoop the soil out
from the slot zone. Further, all of the
designs produce some loose soil on the surface
near the slot, which can be used to
cover the slot again, although in all cases
this usually requires a separate operation
to drag this soil back over the slot (see
Chapter 5) and its effectiveness is soilmoisture-
dependent.
Angled disc-type openers
The action of angled discs is mostly
(although not entirely) one of scuffing. Vertical
angled discs are angled slightly to the
direction of travel (normally about 5–10
degrees). Seed is delivered to a boot located
at or below ground level, close to the rear
(lee) side of the discs where it is largely protected
from blockage by residue because of
the angle of the disc. There are two forms of
angled vertical disc opener.
ANGLED FLAT DISCS (FIG. 4.9). This type uses a
vertical flat disc (i.e. it has no undercutting
action) angled to the direction of travel. The
disc and supporting bearings need to have
considerable inherent strength since the
side forces are quite large, especially when
operating at some speed and/or in plastic
soils that resist sideways movement. Because
the discs continually have a sideways force,
they are often configured in pairs with each
pair of discs at opposite angles so that the
side forces of the entire machine cancel
(see Fig. 4.9).
Where the discs are not arranged in
pairs, difficulty is sometimes experienced
in turning corners in one direction with the
drill, while turning in the other direction
poses no problem. This is another example
in which the requirements of no-tillage are
different from tillage, since the soil forces
in tilled soils are sufficiently low to not
cause problems when cornering with angled
disc-type openers.
Seeding Openers and Slot Shape 41
Fig. 4.9. A pair of angled flat disc no-tillage openers (from Baker et al., 1996).
Relatively steep side-slope drilling
causes machine ‘tailing’, in which the whole
machine pulls at an angle to the direction of
travel because of gravity pulling the drill
sideways. This poses a problem for drills
arranged with half of the openers angled in
each direction. That part of the drill in
which the openers are caused to travel with
no angle creates very small, ineffective seed
slots, while the other openers double their
angle and create extra wide slots that are
difficult to cover.
ANGLED CONCAVE DISCS. This type uses a
slightly concave, near-vertical disc set at an
angle to the direction of travel (Fig. 4.10).
The strength derived from the curvature of
the disc allows thinner steel to be used in
its construction, assisting in soil penetration.
The axle of angled dished discs can be
either horizontal or slightly tilted from the
horizontal in either direction.
If the axle is tilted downwards on the
convex (back) side of the disc, the action of
the disc will be to undercut the soil like a
disc plough. The benefits of this action are
that the displaced soil is not thrown to one
side where it is otherwise often difficult to
retrieve again for covering purposes, as it is
lifted, hinged and inverted. The disadvantages
are that, in soils that are held together
by plant roots (e.g. pasture), a soil flap is
produced, which falls back over the seed.
Since the seed is placed under the ‘hinged’
end of this flap, this can restrict seedling
emergence. Figure 4.11 shows an angled
dished disc that has had a small scraper
added to attempt to slice this flap off.
If the axle is tilted upwards on the convex
(back) side of the disc, it has the effect
of confining the disc action to one of scuffing
only, with little or no undercutting.
Because of the disadvantages of undercutting,
this has become the most commonly
preferred option with concave disc
openers for no-tillage, along with arranging
them with the disc axle horizontal.
TILTED AND ANGLED FLAT DISCS. Some designers
have tilted as well as angled the flat discs
on their openers (Fig. 4.11). This has mainly
been to reduce the throwing action of
angled discs so that there is less soil disturbance
and also to provide more of a mulch
cover than where the discs stand vertically
upright. Tilting the discs may also help
42 C.J. Baker
Fig. 4.10. An angled dished disc no-tillage opener (from Baker et al., 1996).
penetration and reduce the hillside operation
problem discussed above. But it does
nothing to reduce the tendency of such
openers to hairpin residues into the slot,
which interferes with seed germination and/
or seedling emergence. Nor do such openers
solve the problem of fertilizer placement,
since no more opportunity exists to separate
fertilizer from seed than with any other
configuration of angled disc.
The actions of all angled discs (flat or
concave, upright or tilted) are very much
dependent on their operating speed.
Because all variations depend on at least
angulation to the direction of travel (if not
also angulation to the vertical) for much of
their slot-creating actions, the speed with
which they approach the soil has a marked
effect on the amount of soil throw and
therefore the width and shape of the resulting
slot. At higher speeds, the slots tend to
be wider and shallower than at slower
speeds and the loose soil available for covering
tends to be thrown further to one side,
where it is more difficult to retrieve. In
common with discs that travel straight
ahead, the penetration of angled discs is
also reduced with increasing speed, but this
can be countered by simply increasing the
downforce to achieve penetration.
The two biggest advantages of all
angled discs are their ability to handle surface
residues without blockage and their
avoidance of compaction or smearing of the
slot at the base and on at least one side wall.
They are also relatively cheap, simple and
maintenance-free.
The biggest disadvantages of angled
disc openers are: (i) they tuck or hairpin
residues into the slot in a similar manner
to double disc openers; (ii) they make
U-shaped slots, which, especially if wide
at the top, dry easily despite the presence
of loose soil; (iii) they are often difficult
to set for correct operation; (iv) they may
angle and operate poorly on hillsides;
(v) they are not able to separate seed from
fertilizer in the slot; (vi) they are affected
by the speed of travel; and (vii) they wear
rapidly.
Hoe- or shank-type openers
The term hoe or shank describes any shaped
tine or near-vertical leg that is designed to
penetrate the soil. Seed is delivered either
Seeding Openers and Slot Shape 43
Fig. 4.11. An angled dished disc no-tillage opener with both vertical and horizontal angle. This opener
also features a scraper to cut and remove the turf slice. (From Baker et al., 1996.)
down the inside of the hollow tine itself or
down a tube attached to its back.
The shapes of hoe or shank openers
range from winged (Fig. 4.26, p. 54), which
are often also designed to separate seed and
fertilizer simultaneously in the slot, through
blunt bursting openers (Fig. 4.12) to sharp
undercut points, which are designed to
make a relatively narrow slot and penetrate
the soil easily (Fig. 4.13). Sometimes
a pair of narrow shanks is arranged with
horizontal offset to separately place seed
44 C.J. Baker
Fig. 4.12. A blunt hoe-type no-tillage opener (from Baker et al., 1996).
Fig. 4.13. A sharp hoe-type no-tillage opener (from Baker, 1976b).
and fertilizer (Fig. 4.14). One of the problems
with hoe-type openers is that they wear rapidly;
thus, the original shape seldom lasts
long. Because of this they may take on several
new shapes during their lifetime, making
it difficult to generalize on the basis of
slot shape.
Generally, all hoes scrape out a roughly
U-shaped slot by bursting the soil upwards
from beneath. In moist conditions they tend
to smear the base and sometimes the side
walls of the slot, but this only affects seedling
root systems if the soil is allowed to
dry and thus become an internal crust (see
Chapter 5).
The bursting action produces considerable
loose soil alongside the slot, which
may be helpful when covering but can also
leave severe ridging between rows. Because
of this latter problem most shank-type
openers are operated at low speeds (maximum
6–9 kph, 4–6 mph).
The nature and extent of the loose soil
alongside the slot is also dependent on soil
moisture content. Often, in damp plastic
soils, no loose soil will be produced at all,
while at other times a few hours of drying
after drilling will produce crusty edges to
the slots, which can then be brushed with a
suitable harrow or dragged to at least
partially fill the slot with loose soil. The
most appropriate covering action after passage
of hoe-type openers is therefore a matter
of judgement at the time, which is one of
their inherent disadvantages.
The biggest disadvantage of hoe or shank
openers, however, is the fact that they can
only handle modest levels of residues without
blockage (also see Chapter 10), especially
when arranged in narrow rows. The
placement of a leading disc ahead of a hoe or
shank opener, regardless of how or in what
position it is placed relative to the hoe, cannot
make a group of such openers arranged
in narrow rows able to handle residues
satisfactorily.
The most successful hoe or shank drill
configurations for residue clearance have
been to space the openers widely apart in
multiple rows (ranks) in the direction of
travel. This is based on the observation that,
unless the residue is particularly heavy or
damp or becomes wedged between adjacent
openers, the inevitable accumulation of
residue on each tine will usually fall off
to one side, as a function of its own weight.
If sufficient clearance is built into the spacing
between adjacent tines, the falling off
of clumps of residue will not block the
machine – at least, not as often. These
Seeding Openers and Slot Shape 45
Fig. 4.14. A pair of shank openers with horizontal offset. The front shank applies fertilizer
while the rear shank applies seed offset to one side and sometimes shallower.
clumps of residue can cause problems for
seedling emergence and later at harvesting,
so it is questionable whether this action can
be described as handling residue at all.
Unfortunately, wide spacing demands undesirable
dimensions from the whole drill,
which compromises other functions such as
the ability to follow the ground surface and
seed delivery. Figure 4.15 shows a shanktype
no-tillage drill with widely spaced
openers.
Hoe or shank openers have several
advantages: (i) they are relatively inexpensive;
(ii) they can be made to ‘double-shoot’
seed and fertilizer relatively simply; (iii)
they do not tuck (or hairpin) residues into
the slot; in fact, they brush the residue
aside, although this is a disadvantage for
controlling the microclimate within the
sown slot, as described in Chapter 5.
Their major disadvantages are: (i) a
high wear rate; (ii) their poor residue handling
ability; and (iii) their inability to separate
seed from fertilizer in the slot (see
Chapter 9).
Power till openers
Power till openers are an enigma in no-tillage.
Because most people had become accustomed
to tilling the soil before planting seeds, it
seemed natural to till the soil in strips for
no-tillage. Thus, power till openers consist
of miniature rotary cultivators that are
power-driven from a common source and
literally till a series of narrow strips for
the seed. While the tillage ensures that
seeds will become well covered with loose
soil, it has long been known that rotary
tillage is one of the least desirable ways of
tilling soil. Its main disadvantages, when
applied either to general seedbed preparation
or discretely in strips, is that it stimulates
weed seed germination, is very
destructive of soil structure and is powerdemanding
(Hughes, 1975; Hughes and
Baker, 1977).
The actual placement of seed varies
with design. With some, the seed is scattered
into the pathway of the rotating blades
and thus becomes thoroughly mixed with
the soil, but depth of placement becomes
random. With others, separate conventional
openers for tilled soils (shoe, hoe or disc
type) operate behind the rotating blades as
if they were drilling into a fully tilled
seedbed.
The advantages of power till openers
are that the downforces required for penetration
are little more than those commonly
46 C.J. Baker
Fig. 4.15. A no-tillage drill with widely spaced shank-type openers designed to ‘clear’ residues.
required for tilled soils. Power till openers
substitute power applied through the tractor
power take-off (PTO) shaft to the rotors
for the downforces and draft forces more
common to other non-rotating types of
no-tillage openers. They create U-shaped
slots, they do not tuck residue into the slot,
they generally cover the seed well and, in
cold climates, where there might otherwise
be a disadvantage from the slow decomposition
of surface residues, they chop up this
residue and incorporate it into the soil.
On the other hand, because they physically
dispose of the surface residues in this
manner, power till openers do little to
micro-manage the residues close to the
seed, which is one of the most important
functions that successful no-tillage openers
should perform. Further, few of them separate
the seed from the fertilizer in the slot,
although, because of the amount of loose
soil in the slot, there is more mixing of fertilizer
with soil, which provides partial
separation from the seed.
Power till openers are relatively complex
mechanical devices when compared
with other opener designs. They have a
particular problem with wear, surface
following and damage from stones and
other obstructions.
Early designs were adaptations of conventional
field rotary cultivators. The normal
wide L-shaped blades, which were mounted
on a common axle driven by the tractor PTO,
were replaced with sets of narrow L blades
corresponding to the desired row width and
spacing. These created the discrete rows of
tilled soil. The width of the tilled strips varied
from about 20 mm to 200 mm, depending
on the objectives. Figure 4.16 shows the
effects from a narrow set of blades, while
Fig. 4.17 shows wider tilled strips.
In early designs each set of blades was
mounted on a common axle, so it was
impossible for each tilled strip to maintain a
constant depth while traversing the normal
undulations of the ground. Even the use of
independently articulated seed-depositing
openers, which followed in the tilled strips,
could not fully compensate for areas of
soil that had missed being tilled altogether
because the machine had traversed a
small hollow, for example. Figure 4.16 shows
a common-axle-type power till drill with
independently mounted seed-depositing
openers.
Seeding Openers and Slot Shape 47
Fig. 4.16. Narrow tilled strips left by a power till ‘no-tillage’ opener (from Baker et al., 1996).
Later designs attempted to mount each
rotating set of blades independently so that
they were capable of following the soil surface.
This proved to be inordinately expensive,
because, while each set of blades
required its own flexible drive train, it also
had to offer some protection from stone
damage. Belt drives allowed slippage in
these circumstances.
Some designs compromised by mounting
blade sets in pairs. Figure 4.18 shows
the head of a twin rotor model in which
the rotors are able to articulate up and
down. Other designs attempted to power
48 C.J. Baker
Fig. 4.17. Wide tilled strips left by a strip-tillage machine (from Baker et al., 1996).
Fig. 4.18. Power till no-tillage openers arranged in pairs (from Baker, 1981a, b).
each rotor individually through a chain
driven by a wavy-edged ground-engaging
disc ahead of the rotor in the hope that the
disc would slip in the soil when a stone was
encountered by the rotor. Figure 4.19 shows
such a device.
Although power till openers have been
an obvious design route for many engineers,
with a number of models released for commercial
production around the world, very
few have been commercially successful
due to the disadvantages mentioned above.
Perhaps their greatest use is where other
openers cannot function. An example of such
a condition is the revegetation of highaltitude
pastures where ambient temperatures
remain sufficiently low to discourage
complete decomposition of organic matter.
The result is a build-up, over centuries, of a
mat of undecomposed vegetation, which
can be several centimetres thick (Fig. 4.20)
and which simply resists the operation of
any other no-tillage opener except designs
that physically chop it up and mix it with
soil. In these conditions, the objective is to
drill improved pasture species by no-tillage
to increase animal carrying capacity on
otherwise low-producing fragile farmland.
Power till openers in general create
more short-term mechanical aeration within
the slot than any other type of opener,
although the benefits of this are usually
temporary in comparison with openers that
encourage natural aeration by earthworms
(see Chapter 7). They have a tendency to
compact the base of the slot, but, unlike
double disc openers, this does not seem to
cause difficulties for seedling roots.
Furrowers
One opener, designed in England especially
for pasture renovation, consisted of
two vertical discs, spaced laterally several
centimetres apart, which cut two vertical
slits. The discs were followed by a miniature
mouldboard-plough, which scooped
out the soil between the slits at the same
time as it created a small track in the base
of the broad U-shaped slot, where seed was
deposited (Haggar, 1977; Choudhary et al.,
1985). The function of scooping was to
eliminate weed competition in the seed
zone without spraying and to allow early
seedling development to take place in a
sunken zone physically protected from
Seeding Openers and Slot Shape 49
Fig. 4.19. A power till no-tillage opener driven by a ground-engaging wavy disc (from Baker et al., 1996).
treading by cattle (Fig. 4.21). Seed cover in
the damp English climate is not a high
priority, but such openers are regarded as
specialist tools designed solely for one
intended purpose.
Vibrating openers
Several designers have attempted to reduce
the downforces required to push the discs
and other components of no-tillage openers
50 C.J. Baker
Fig. 4.20. Undecomposed sod in the Scottish Highlands (from Baker, 1981a, b).
Fig. 4.21. A furrowing no-tillage opener (from Choudhary et al., 1985).
into the ground by causing the openers to
vibrate. Such a task has been particularly
demanding when applied to a disc since the
vibration mechanism needs to operate on
the disc hub as it rotates, as well as moving
up and down in response to natural undulations
in the ground surface. Individual
vibrating hydraulic motors have been used
on individual openers, which increase the
cost, complexity and power requirement
considerably. Very slow operating speeds
and difficulty in keeping all bolts and nuts
tight because of the general vibrations generated
throughout the machine have also
been disadvantages.
In the end, it is the shape and action of
the soil-engaging components that determine
the biological success or otherwise of
no-tillage openers more than the forces
required for penetration of draught. Vibrating
openers do nothing to improve biological
reliability. Most designers have found it
cheaper to add weight and/or use a larger
tractor to overcome penetration and draught
forces than to engage relatively complex
vibrating devices.
Horizontal Slots
Inverted-T-shaped slots
All of the openers discussed so far have
been adaptations of openers designed originally
for tilled soils (with the exception of
the specialized furrow and vibrating openers).
The modifications to such openers,
when employed for no-tillage, have mostly
consisted of increased robustness, with
only minor changes in function.
The inverted-T-shaped slot is the only
known horizontal no-tillage slot shape and
is one of very few slot shapes that have
been developed specifically for no-tillage
purposes, with few functions applicable to
tilled soils.
The inverted-T principle was developed
when researchers explored geometrical
alternatives to the more common V and
U slot shapes to overcome several of
their inherent disadvantages (Baker, 1976a).
The researchers reasoned that the most
radically different shape would be to invert
the wide-top narrow-base V shape and to
create instead a narrow-top, wide-base slot.
Practicality dictated that the simplest way
to achieve this was to construct an opener
consisting of a vertical shank with subsurface
wings that were horizontal in the
lateral plane but inclined downwards
towards the front in the longitudinal plane.
The other reasoning behind the winged
concept was that the designers wanted to be
able to fold the residue-covered soil back over
the slot for moisture conservation and seedling
protection. Since wings tended to undercut
the surface layer of soil with a horizontal
slicing action, this would allow the formation
of horizontal shelves on either side of a vertical
slit. In most conditions the wing action
also created horizontal flaps of residuecovered
soil with which to cover the shelves.
It was a major objective of the inverted-T concept
to create horizontal slots with a high
degree of control and predictability.
Two winged opener concepts were
developed, both of which created essentially
the same inverted-T-shaped slots.
Simple winged opener
The first simple winged opener design consisted
of a vertical shank attached to the
bottom of a hollow tine (Baker, 1976a, b).
Figure 4.22 shows the original winged
opener design. The opener was hollow, to
allow passage of seed, and open at the back.
The shank curved out at its base on both
sides to form a pair of symmetrical wings,
which were downwardly inclined towards
their fronts by 10° and projected laterally
approximately 20 mm either side.
A leading vertical flat disc was used
ahead of the shank to provide a neat vertical
cut through pasture. The leading disc was
not expected to give the opener an ability to
clear lying surface residue (see Chapter 10),
but to ensure passage of the opener through
standing pasture (sod) with minimal tearing
and disruption to the soil surface.
A commercial company in New Zealand
successfully adapted the winged opener
concept for pasture renovation purposes.
This market opportunity was based on
Seeding Openers and Slot Shape 51
knowledge that there is six times as much
area of the world’s surface under grazing
land as there is under arable crop production
(Kim, 1971; Brougham and Hodgson,
1992), although, of course, not all of the
world’s grasslands are accessible to tractors.
The design was simplified by fashioning
the shank from plate steel and welding a
vertical flat plate to its rear edge so as to
entrap a wedge of soil ahead of this zone.
Seed delivery was altered from the hollowed
opener itself to a permanent tube
positioned behind the vertical flat plate.
The reasoning had been that, as the opener
became worn and was eventually discarded,
the modified design would allow
the seed tube component to remain and
only the minimum possible amount of
replacement component would be discarded,
thus reducing the cost. It was also
reasoned that the soil wedge trapped ahead
of the flat plate would reduce wear of the
opener in that zone. Later, other designs
also provided reversible and replaceable
leading edges and tungsten overlays on the
opener in an attempt to further reduce the
effects of wear. Figure 4.23 illustrates a
number of versions of the same modified
opener, which eventually became known
generically as the ‘Baker boot’, after the
originator of the inverted-T principle.
Unfortunately, some of these benefits in
the modified designs were achieved at the
cost of retaining control over the exact shape
of the slot. The thickness of the soil wedge
that is retained by the vertical flat plate is a
function of soil type, stickiness and moisture
content. As a result, in sticky soils it is common
for this soil wedge to become wider
than the wings beneath it, with the result
that the intended function for the wings to
undercut the surface layer of soil is lost and
the opener at times functions more as a
wedge, creating a U-shaped slot.
52 C.J. Baker
Fig. 4.22. The original
inverted-T-shaped no-tillage
opener (from Baker, 1976b).
Although several manufacturers produced
almost identical versions of the
modified opener, not all of them provided
a leading disc as originally envisaged, with
the result that the slot edges were often
torn and inconsistent, making controlled
closure of the slot difficult, if not impossible.
Since low cost was a primary objective
with this simple opener, most designs
attached the opener to very simple drills
that had limited depth control (Fig. 4.24).
One design provided a vertical pivot ahead
of each opener to assist with cornering
(Fig. 4.25).
Despite these shortcomings, the modified
version of the simple inverted-Tshaped
opener succeeded in its intended
purpose of pasture renovation. Its principal
advantage has been that the inverted-Tshaped
slot, however poorly made, is
demonstrably more tolerant of dry and wet
soil conditions (see Chapters 6 and 7) than
nearly all other opener designs, with the
result that the success of the pasture renovation
process improved noticeably.
The largest disadvantages of this opener
have been that, by being a rigid shank, it has
poor residue-handling qualities and speed of
operation is limited. Where it is incorporated
on simple drills, surface-following
ability is limited.
Other designers have utilized the winged
opener concept to separate the discharge
of seed and fertilizer into two or more
horizontal bands (double or triple shoot).
Figure 4.26 shows a double-shoot winged
opener.
Winged opener based on a central disc
Given the superior biological results obtained
with the inverted-T-shaped slot concept
from numerous experiments conducted in
Seeding Openers and Slot Shape 53
Fig. 4.23. Several versions of the ‘Baker boot’ inverted-T-shaped no-tillage opener (from Baker et al.,
1996).
Fig. 4.24. A simple drill featuring ‘Baker boot’
inverted-T-shaped no-tillage openers (from
Baker et al., 1996).
New Zealand, Canada, Australia, Peru and
the USA, it became imperative that the
shortcomings of the simple opener should
be overcome by designing a version that
would suit arable agriculture as well as
pasture-land. After all, it is the repeated tillage
of arable land that has damaged the
world’s most productive soils. The potential
of no-tillage to reverse this process is fundamental
to the long-term sustainability of
world food production.
A number of functional principles
were considered essential if such an opener
were to become fully capable of such an
assignment:
1. The most important aspect was to
maintain the inverted-T shape of the slot
itself, even at high forward speeds and
shallow seeding depths.
2. Ability to reposition loose residue on
top of loose soil to cover the horizontal
slot, as well as to fold back more structured,
previously untilled material such as flaps
of turf.
3. Effective separation of seed and fertilizer
in the slot with a single opener, and to
perform this function reliably over a wide
range of soil type, moisture contents and
forward speeds.
4. Handling without blockage of surface
residue, even when configured in narrow
(150 mm, 6 inch) rows, in difficult conditions
ranging from dry or wet crop stubble
to tangled, well-rooted sod, on soils ranging
from soft and wet to hard and dry.
54 C.J. Baker
Fig. 4.25. A simple drill featuring a self-steering version of the ‘Baker boot’ inverted-T-shaped
no-tillage opener.
Fig. 4.26. Two versions of double-shoot winged
openers.
5. Self-closure of the slot without undue
soil compaction for seedling emergence.
6. Capability to maintain a constant seeding
depth by consistently following the
ground surface.
7. Replacement parts to be inexpensive and
easily removed and replaced in the field.
The resulting design, shown in Fig. 4.27,
has working principles quite unlike other
openers designed for either tilled or
untilled soils (Baker et al., 1979c). Essentially,
the disc version of the winged opener
arose from splitting the simpler winged
opener both vertically and longitudinally
and rubbing the insides of the leading edges
of the two sides against a central disc. It is
centred on a single flat vertical disc (smooth
or notched) running straight ahead to cut
the residue and the vertical portion of the
soil slot. Two winged side blades are positioned
so that the interior of their leading
edges rubs on either side of the central
disc. This patented principle effectively
sheds residue from the side blades without
blockage.
The winged side blades cut horizontal
slots on either side of the disc at seeding
depth by partially lifting the soil. Seed and
fertilizer flow down special channels
between the side blades and the disc on
either side, respectively, and are placed on
the horizontal soil shelf. To achieve this,
the side blades are held sufficiently clear of
the disc at their rear edges to form a passageway
for seed or fertilizer. Such a gap is
narrow in comparison with other opener
designs but movement of even large seeds is
facilitated by the fact that one side of the
passageway comprises the moving face of
the revolving disc.
The fertilizer blade can be made slightly
longer than the seed blade so that the fertilizer
can be separated vertically from the
seed as well as horizontally, i.e. diagonally,
although in most circumstances horizontal
separation has proved to be sufficient, if not
preferable (Fick, 2000).
Two angled semi-pneumatic wheels
follow the blades to reset the raised soil
and residue, thereby positively closing the
slot. They also regulate the depth of each
opener independently for excellent soil
surface tracking and thus precise seed
depth control. Each opener is mounted on
parallel arms necessary to maintain the
shallow wing angle at seeding depth for
tracking the soil surface.
Figure 4.28 is a diagrammatic representation
of the horizontal seed and fertilizer
separation (double shoot) with the disc version
of a winged opener. Separating seed
and fertilizer and sowing both with the
same opener greatly simplify the design of
no-tillage drills and reduce power demand.
Fertilizer banding has become an essential
function of successful no-tillage seeding for
most crops (see Chapter 9). Few, if any,
other no-tillage openers effectively and
simultaneously achieve these important
functions in a wide range of soils and at
realistic forward speeds.
The opener is designed especially for
no-tillage into heavy surface residues and
grass sod where simultaneous sowing of
seed and fertilizer is a priority. Because
the incline on the wings is set at only 5° to
the horizontal (compared with 10° for the
Seeding Openers and Slot Shape 55
Fig. 4.27. A disc version of the winged opener
for creating inverted-T slots.
simple inverted-T version), it is capable
of drilling at depths as shallow as 15 mm. It
functions equally well, without modification,
in heavy crop residues, pastures and
sports turf (Ritchie, 1988), and can be used
unmodified to sow the full range of field
crops and pasture seeds, as well as for precision
drilling of vegetables (Ritchie and
Cox, 1981), maize and horticultural crops. It
commonly retains 70–95%, of surface residues
intact. Figure 4.29 shows 95% residue
retention after passage of a disc-version
inverted-T opener.
The main advantages of the disc version
of the inverted-T-shaped opener are
that it fulfils all of the design objectives
listed above, without compromise. The same
opener can be used unmodified for precision
seeders, as well as grain drills and pasture
renovation machines, in tilled and no-tillage
farming.
Its disadvantages are that it has a slightly
higher draught requirement, is relatively expensive
to construct and requires a heavy drill
frame design to ensure proper functioning.
The relatively high cost can be weighed
against its ability to maximize and even
improve crop yields beyond those commonly
experienced with other no-tillage openers
and even tillage (Saxton and Baker, 1990). An
apparent economic disadvantage when put in
the fuller context becomes very cost-effective.
Punch Planting
Punch planters make discrete holes into
which one or more seeds are placed before
moving on to the next hole. Ancient farmers
used pointed sticks to make the holes
because there was insufficient energy to
make continuous slots and utilize the convenience
of continuous flow of seed and
fertilizer into them.
Modern engineering has attempted to
mechanize punch planting so that it can be
performed with less human labour and with
greater accuracy and speed. The devices
created have mostly consisted of steel wheels
with split spikes attached to their rims. The
split spikes are hinged at their bases so that
they can be forced to open in much the same
way as a bird’s beak. Figure 4.30 shows an
example of a prototype mechanized punch
planter.
In operation, the opening and closing
functions are actuated by an internal cam
and synchronized with a seed dispenser.
56 C.J. Baker
Fig. 4.28. Horizontal separation of seed and
fertilizer by the disc version of a winged opener.
Fig. 4.29. Almost complete replacement of
residues over the slot created by a disc version of
an inverted-T-shaped opener (Class IV cover).
After each spike has become fully embedded
in the soil, a single seed or small group of
seeds is directed from the dispenser tube,
located in the centre of the wheel, through a
hole in the rim of the wheel into the opened
spike and deposited in the soil at a controlled
depth and spacing from its neighbours.
Mechanized punch planters were seen
as sensible solutions to mechanizing an
ancient practice. Their relative mechanical
complexity, however, has prevented their
widespread adoption to date. The creation
of V-shaped holes has all of the biological
disadvantages of continuous V-shaped slots.
This includes the tucking (hairpinning) of
residues into the holes, difficulty in closing
the holes and the wedging action of the
spikes, which compacts soil under and
alongside the seed zone.
Surface Broadcasting
There is little need to elaborate on the practice
of surface broadcasting. Again, it is
derived from an ancient practice brought
about by the absence of energy sources
for more mechanized solutions. Certainly,
modern machinery is capable of mechanizing
the broadcasting process with much
increased speed and accuracy, but the absence
of positive placement of seed beneath
the soil significantly increases the biological
risks from desiccation and bird, insect
and rodent damage.
Broadcasting is not a recommended
practice except in low-energy situations, and
only then where local rainfall and humidity
are so predictable and reliable that germination
and rooting are assured. One thing in
favour of no-tillage is that the retention of
dead surface residues provides a protective
canopy beneath which the humidity is likely
to be higher than the surrounding ambient
air (see Chapter 6). Research for many years
has shown that effective seed and fertilizer
placement beneath the soil produces crop
yield advantages that surface broadcasting
cannot duplicate.
One solution to broadcasting that reduces
risk is ‘auto-casting’ in which seed is
broadcast mechanically behind the pickup
table of a combine harvester. The objective
is to allow the straw and chaff to fall on
top of the seed at the rear of the machine.
This in turn ensures that there is a degree of
Seeding Openers and Slot Shape 57
Fig. 4.30. A prototype mechanized punch planter (from Baker, 1981a, b).
cover over the seed, but success with this
method is still very weather-dependent and
there is no opportunity to strategically
place fertilizers at the time of seeding. A dry
period following harvest increases the risks
of failure. Figure 4.31 shows an auto-casting
system attached to the rear of a combine
harvester table.
Summary of Seeding Openers and
Slot Shape
The important functions of seeding openers
are their abilities to:
1. Create a suitable seed/seedling microenvironment.
2. Avoid compacting and smearing of the
slot walls.
3. Handle surface residues without blockage.
4. Micro-manage the surface residues so
that they are positioned where they are of
most advantage to the sown seeds/seedlings
as well as the field in general.
5. Band seed and fertilizer simultaneously
in the slot but separate them so as
to avoid ‘seed burn’.
6. Either avoid hairpinning altogether
or avoid hairpinned residues affecting seed
germination.
7. Self-close the slot.
8. Accurately control the depth of seeding.
9. Faithfully follow surface undulations
that occur naturally in no-tillage.
The variety of slot shapes made by
no-tillage seeding openers can be summarized
as:
1. Vertical or horizontal.
2. Vertical slots are either V- or U-shaped.
3. Horizontal slots are usually inverted-
T-shaped.
4. V- and U-shaped slots may also be
slanted as well as vertical.
5. Compared with continuous slots, seeds
can be sown in discrete holes (punch planting)
or by surface broadcasting, mostly used
where energy is limiting.
6. Most vertical and some slanted V- and
U-shaped slots are adaptations of slots originally
designed for tilled soils.
7. Most horizontal inverted-T-shaped slots
were designed specifically for no-tillage
seeding.
8. V-shaped slots are mainly created by
double or triple disc openers.
9. U-shaped slots may be created by hoe,
angled flat disc, angled dished disc, power
till or furrow openers.
10. Inverted-T-shaped slots are created by
winged openers.
58 C.J. Baker
Fig. 4.31. ‘Auto-casting’ of seed behind the pickup table of a combine harvester.
11. The practices of punch planting and
broadcasting have ancient origins but have
also been mechanized.
12. There are higher risks of poor plant
establishment associated with surface broadcasting
than where seed is sown beneath
the soil by openers.
The action of openers on the soil varies
by the opener design as:
1. Vertical double disc openers in the soil
predominantly cut, wedge and compact.
2. Slanted double disc openers cut and
heave on the uppermost side and compact
on the lowermost side.
3. Punch planters wedge and compact.
4. Hoe openers mostly heave and burst,
plus cut if preceded by a disc.
5. Power till openers cut, mix and pulverize.
6. Vertical angled flat disc openers cut,
scuff and throw.
7. Angled dished disc openers and
slanted angled flat disc openers cut, scuff,
fold and/or throw.
8. Winged openers heave and fold, plus
cut if associated with a disc.
The advantages and disadvantages of
various openers by design are:
1. Double and triple disc openers are
low-maintenance and have good residue
handling. Their disadvantages are V-shaped
slots, especially when configured vertically;
unreliable seedling establishment;
high penetration forces; compaction and
smearing of soil; difficulty in covering; no
separation of seed and fertilizer (unless
doubled up); seed implantation into
hairpinned residue.
2. Punch planter openers are low-energy
and maintenance. Their disadvantages are
mechanical complexity, slowness, hole
compaction, difficulty in covering and no
separation of seed and fertilizer.
3. Hoe openers are low-cost, no
hairpinning of residue and reasonable penetration
forces. Their disadvantages are
poor residue handling, high wear rates,
smearing in wet soils and no separation of
seed and fertilizer unless doubled up.
4. Power till openers mix undecomposed
organic matter with soil, do not hairpin residue,
low penetration forces, burial of seed
and dilution of fertilizer with soil. Their
disadvantages are poor residue handling,
residue destruction, tillage, slot-base compaction,
difficulty in handling stones and
sticky soils, cost, mechanical complexity,
weed seed stimulation, high maintenance
and no ability to separate seed and
fertilizer.
5. Vertical angled flat disc openers have
reasonable penetration forces, scuffing
action, residue handling and no smearing or
compaction. Their disadvantages are seeding
into hairpinned residue, no separation
of seed and fertilizer (unless doubled up)
and affected by forward speed.
6. Angled dished disc openers and
slanted angled flat disc openers have scuffing
action, residue handling and no smearing
or compaction. Their disadvantages are
high penetration forces, seed implantation
in hairpinned residue, no separation of seed
and fertilizer (unless doubled up) and
affected by forward speed.
7. Simple winged openers provide horizontal
inverted-T-shaped slots that are easily
closed, reliable seedling emergence, no
compaction, reasonable penetration forces
and do not hairpin residues. Their disadvantages
are poor residue handling, high
wear rates and no separation of seed and
fertilizer.
8. Disc versions of winged openers (centred
on a vertical disc) provide horizontal
inverted-T-shaped slots, self-cover slots,
reliable seedling emergence, horizontal or
diagonal separation of seed and fertilizer,
good residue handling and micromanagement,
no seed implantation in
hairpinned residue, capable of high forward
speeds, low compaction, low weed seed
stimulation, good depth control and low
maintenance. Their disadvantages are high
initial costs, high penetration forces, and
high draught.
Seeding Openers and Slot Shape 59
5 The Role of Slot Cover
C. John Baker
In no-tillage, nothing influences the reliability
of seedling emergence more than the nature
of the slot cover.
If you stand on the ground and look down
on a seeded soil slot (‘furrow’ or ‘groove’),
after passage of a no-tillage drill or planter,
you will see varying types of seed and slot
coverage, which we have described in five
‘classes’ (Baker et al., 1996):
1. Class I: visible seed (Fig. 5.1). Little or
no loose soil covering the seed.
2. Class II: loose soil (Fig. 5.2). Loose soil
and perhaps a small amount (less than 30%)
of surface residue or mulch that has been
induced back into the slot to cover the seed.
3. Class IIIa: intermittent mulch and soil
(Fig. 5.3). There is a variable amount (30%
or more) of residue or mulch on top of the
loose soil covering the seed.
Class IIIb: a mixture of residue and soil
(Fig. 4.17). Thirty per cent or more of residues
or mulch is mixed in with, rather than
on top of, the loose soil covering the slot.
4. Class IV: complete mulch and soil
(Figs 5.4 and 5.5). Soil and a covering of at
least 70% of residue or mulch has been
induced back over the slot in roughly the
same layering positions as they were prior
to drilling, i.e. with the mulch covering the
soil, which in turn covers the seed.
The basis of these classifications
was described by Baker (1976a, b, c) and
Baker et al. (1996), who observed that,
where an intermittent mulch/soil cover
© FAO and CAB International 2007. No-tillage Seeding and Conservation
60 Agriculture, 2nd edn. (eds C.J. Baker and K.E. Saxton)
Fig. 5.1. Visible seed in Class I no-tillage slot
cover (from Baker et al., 1996).
(Class IIIa) occurred under dry conditions,
seedlings were seen to emerge from under
a flap of dead turf (mulch) or even a piece
of random residue and soil, but had
not emerged from where the seed cover
was confined to loose soil alone or where
there was no cover at all. This suggested
that loose soil may not have been the ultimate
seed cover as had been previously
assumed.
Role of Slot Cover 61
Fig. 5.2. An example of Class II no-tillage slot cover (from Baker et al., 1996).
Fig. 5.3. An example of Class IIIa no-tillage slot cover (from Baker et al., 1996).
In fact, some engineers and agronomists
continue to mistakenly assume, even
today, that the best cover for seeds is loose
soil (Class II). This assumption comes from
what has been provided in a tilled seedbed
for centuries. Residues do not exist to any
degree on well-tilled soils. Generally, they
have been buried or burnt prior to tillage.
62 C.J. Baker
Fig. 5.4. An example of Class IV no-tillage slot cover in heavy standing wheat stubble and scattered
straw (from Baker et al., 1996).
Fig. 5.5. An example of Class IV no-tillage slot cover in sparse close-growing weeds. Note the
replacement and layering of whatever residue is available in its original position and the absence of soil
inversion after passage of the drill. (From Baker et al., 1996.)
The only other resource available for covering
in addition to clean, loose soil is perhaps
a press-wheel effect to provide slightly
compacted soil, but even the benefits of
that are dubious. So loose soil has been
regarded as the ‘ultimate cover’, at least in a
tilled soil.
Based on the ‘loose-soil-is-best’ assumption,
some engineers therefore postulated
that all that was needed for no-tillage was to
till the soil in a series of strips and sow seed
into the tilled strips as you would in a generally
tilled soil, but, in this case, leaving
the rest of the seedbed untilled between
the strips. This is one form of strip (or zone)
tillage, which has been described previously
in Chapter 4.
Unfortunately, this simplistic view has
no scientific basis and it is now known that
it destroys several of the very special
resources close to the seed that most untilled
soils have, such as a mulch covering, an
unbroken macropore system within the
seed zone and an equilibrium soil humidity
near 100%.
The Role of Soil Humidity
The atmosphere in the macropores within
an untilled residue-covered soil has an
equilibrium humidity of very near 100%
(Scotter, 1976) at almost all moisture levels
down to ‘permanent wilting point’, which
is when a soil is too dry for plants to survive.
In fact, it is 99.8% even at wilting
point (1500 kPa tension). In no-tilled seeding,
the soil is only broken at the surface by
strips (slots) where the drill or planter
openers have travelled. The greatest loss of
humidity from the soil to the atmosphere
occurs at these broken strips (slots). The
aim, therefore, of drilling into dry soils
should be to create slots that do not encourage
loss of humidity from these zones, since
they are also the zones where the seeds are
placed, which require moisture to initiate
plant growth.
The classification of covers listed
above is arranged in order of ascending
humidity retention. A ‘complete’ (70% or
greater) mulch/soil cover (Class IV) retains
more humidity than an intermittent mulch
and soil cover (30 to 70% residue – Class
III), which is better than loose soil (less than
30% – Class II), which itself is better than
no cover at all (Class I).
Choudhary (1979) and Choudhary and
Baker (1981b) measured the daily loss of
relative humidity (RH) from a range of different
slot shapes under controlled dry conditions
with constant temperature. They
used the average daily RH loss for the first
3 days following seeding to compute an
index value for the ability of a slot to retain
humidity, moisture vapour potential captivity
(MVPC).
MVPC = 1/(average 3-day RH% loss)
Table 5.1 lists results from two separate
experiments in which Choudhary placed a
small humidity probe in positions that would
normally be occupied by the seeds within
drilled slots in a dry soil. Undisturbed
soil bins (weighing 0.5 t each) were
placed within climate-controlled rooms at a
Role of Slot Cover 63
V-shaped slot
(Class I cover)
U-shaped slot
(Class II cover)
Inverted-T-shaped
slot (Class IV cover)
Daily loss
of RH% MVPC
Daily loss
of RH% MVPC
Daily loss
of RH% MVPC
Experiment 1 4.23% 0.24 2.78% 0.36 2.34% 0.43
Experiment 2 3.13% 0.32 2.03% 0.49 1.02% 0.98
Mean 3.68% 0.28 2.41% 0.43 1.68% 0.71
MVPC, moisture vapour potential captivity = 1/(average 3-day RH% loss).
Table 5.1. Effect of no-tillage slot shape and cover on slot drying rates and MVPC.
constant ambient temperature and constant
RH of 60%.
Relative humidity is a measure of the
amount of water vapour in the soil atmosphere
at any one temperature. The source
of supply of water vapour in the drilled
slots is from the surrounding soil since its
equilibrium relative humidity is always
near 100%, but the rate of escape of water
vapour to the atmosphere outside the soil
(which is usually less than 100% RH unless
it is raining or there is thick fog) is controlled
by the diffusion-resistance to gases
passing through the covering medium in or
on the slot. For at least a few days after drilling,
the soil temperatures (even in the slot)
can be expected to remain at reasonably
constant levels (Baker, 1976a). Therefore,
measurements of relative humidity in the
slots at these constant temperatures closely
reflect the amount of water vapour (or the
water vapour pressure) in the slot at the
time.
The higher MVPC values (or lower
daily losses of RH%) for Class IV covers
indicate that such a slot had a higher potential
to retain in-slot water vapour than
Class II cover, for example, which itself had
a higher water vapour retention and lower
daily loss of RH% than Class I cover. The
Class IV cover in these experiments was, in
fact, 65% better than Class II and 154%
better than Class I in retaining in-slot
humidity. No Class III cover was included
in this experiment.
The effects of moisture transfer from
the slot micro-environments was also studied
by varying the overlying air humidity
at a constant temperature (Choudhary,
1979; Choudhary and Baker, 1980, 1981b).
The humidity within the slots increased
differently as the ambient RH was raised
from 60% to 90%. Those slot shapes that
increased most rapidly with a rise in ambient
humidity will obviously decrease (dry)
most quickly after sowing and be less
favourable to seed germination and plant
establishment. The most rapid change was
in the open V-shaped slots (Class I cover),
which increased at the rate of 8% RH per
day, followed by the U-shaped slot (Class II
cover), followed by the inverted-T-shaped
slot (Class IV cover), which increased by
only 1% RH per day.
For the inverted-T-shaped slot (Class
IV cover), the rate of re-moistening was
about the same as its rate of drying (i.e.
approximately 1% RH per day), but for the
V-shaped slot (Class I cover) the rate of
re-moistening was about twice that of its
drying. This confirmed that Class I cover
had done little to isolate the slot microenvironment
from changing ambient conditions,
while Class IV cover had effectively
isolated the slot from such climatic changes
and retained a highly humid slot atmosphere
throughout.
From a practical point of view, if seeds
are sown into a favourable soil and the following
week is dominated by hot dry
winds, a slot that might have presented an
ideal habitat for the seeds at the time of
sowing can soon turn into a hostile environment
unless the slot is protected from such
climatic changes by adequate slot cover.
Choudhary and Baker (1982) showed that
no-tillage slots with Class IV cover allowed
seed germination and seedling emergence
from soils that were otherwise too dry to
germinate seeds sown by either conventional
tillage or with other no-tillage openers
and slots.
A field experiment in Manawatu,
New Zealand, before Class IV cover had been
fully evaluated (Baker, 1976a, c) illustrated
that loose soil (Classes II and III cover)
is much better than no cover at all (Class I
cover). In this experiment, a barley (Hordeum
vulgare) crop was sown in late spring using
hoe openers (U-shaped slot) in a silt loam
soil with adequate moisture. One half of the
sown rows was covered by pulling a bar
harrow over the slots (Class IIIa cover)
and the other half was left as the drill had
created the slots (essentially uncovered,
Class I). The period after drilling was hot,
dry and windy. Eight days after sowing the
Class IIIa covering had 205 plants/square
metre, compared with the Class I cover,
which had only 22 plants per square metre.
An experiment conducted at the same
time and in the same soil showed that
increased seed size did not compensate for
poor covering. Where larger seeds might have
64 C.J. Baker
been expected to have more vigour and
therefore be able to compensate for emergence
difficulties, the opposite seemed to
have happened under no-tillage. In this
experiment a small-seeded species, lucerne
(Medicago sativa), and a large-seeded
species, maize (Zea mays), were substituted
for barley and no-tilled in exactly the same
manner. After 10 days, the small-seeded
lucerne had 118 plants per m2 under Class
IIIa cover and 87 under the Class I cover.
After a similar length of time the maize had
4.6 and 0.3 plants per m2, respectively, for
the two classes of cover.
While Class IIIa cover still increased
seedling emergence with both the larger and
smaller seeds, the increase was less with
lucerne than with either maize or barley.
The smaller lucerne seeds apparently had a
better chance of finding themselves covered
with a small piece of soil or mulch, which
produced a favourable micro-environment
for them, even in a Class I situation, than
did the larger barley seeds, which were
better placed than the even larger maize
seeds in this respect.
A few days after the measurements of
this experiment, rain ensured that all seeds
germinated in all three of the experiments
and the differences between treatments disappeared.
Thus, the effects of cover were
only important when the soil was dry or
drying, although, as described in Chapter 7,
cover is also important in wet conditions
for other reasons.
As further evidence of the importance
of cover in both wet and dry soils, Table 5.2
summarizes the ‘best’ and ‘worst’ treatments
of 30 experiments conducted in New Zealand
between 1971 and 1985. Each experiment,
amongst other things, compared the effects
of different openers and classes of cover
under different soil moisture conditions on
seedling emergence of a range of crops
(Baker, 1979, 1994).
There are several clear trends to be seen
in the Table 5.2 data, and the experiments
are grouped accordingly. The first is a tendency
towards improving seedling emergence
with Classes III and IV covers, where
surface residues were present and the soils
were either very dry (experiments 1–12)
or very wet (experiments 25–30). As the
moisture conditions became more optimal
(experiments 13–18) and/or when surface
residues were not present (experiments
19–24), the difference between the classes of
cover generally became less or non-existent.
Perhaps just as important was the magnitude
of some of the differences. Two- to
14-fold differences are rare in agricultural
experimentation, suggesting that slot shape
and cover have a major influence on the
reliability and success of no-tillage practices,
a fact not formerly recognized or reported.
Even a ratio of 1.2 : 1 represents a 20%
advantage for the ‘best’ treatment.
It is also notable that, where Classes I
and II covers were included in the comparisons,
they were almost invariably classed
either as the ‘worst’ treatment or as ‘no
better than’ the other treatments. They
seldom outperformed any other treatment,
the exceptions being in two very wet soils
without residue, where seedling emergence
was low with all of the openers compared.
On the other hand, Classes III and IV cover
were never bettered by any other treatment
in the presence of surface residues in wet,
optimum or dry soils.
The Table 5.2 data include only the
‘best’ and ‘worst’ treatments for simplicity.
Comparisons of other intermediate treatments
between these two extremes are not
shown. Almost invariably, however, Class
IV cover produced greater seedling emergence
than Class III cover, which in turn
outperformed Class II cover, especially in
dry conditions. More detailed descriptions
of these comparisons are given in Chapters
6 and 7.
Methods of Covering Seed Slots
There are several principles involved in
covering slots after the passage of no-tillage
openers, and these are often combined with
pressing to obtain soil–seed contact. These
methods are:
1. Squeezing – attempting to move soil
sideways into the slot by a wedging action
to cover and to obtain soil–seed contact.
Role of Slot Cover 65
66 C.J. Baker
Year Soila Crop
Soil moisture
and residue
statusb
Best and worst treatments
and classes of cover
(best) : (worst)c
Ratio of seedling
emergence counts
(best) : (worst)
1 1979 S/L Wheat V. dry (R) inv. T/C (IV) : t.d. V/C (I) 14 : 1
2 1971 S/L Maize Dry (R) hoe U/C (III) : hoe U (I) 14 : 1
3 1971 S/L Barley V. dry (R) hoe U/C (lll) : hoe U (I) 9.5 : 1
4 1972 S/L Barley V. dry (R) inv. T/C (IV) : hoe U/C (II) 6 : 1
5 1979 FS/L Wheat V. dry (R) inv. T/C (IV) : t.d. V/C (I) 5.5 : 1
6 1976 FS/L Wheat Dry (R) inv. T/C (IV) : t.d. V/C (I) 3 : 1
7 1971 S/L Kale Dry (R) hoe U/C (III) : hoe U (I) 2 : 1
8 1979 S/L Wheat V. dry (R) inv. T/C (IV) : t.d. V/C (I) 1.7 : 1
9 1979 FS/L Wheat Adeq. (R) inv. T/C (IV) : t.d. V/C (I) 1.6 : 1
10 1979 S/L Lucerne V. dry (R) hoe U/C (III) : hoe U (I) 1.4 : 1
11 1979 S/L Wheat V. dry (R) inv. T/C (IV) : t.d. V/C (I) 1.3 : 1
12 1979 S/L Wheat Dry (R) inv. T/C (IV) : t.d. V/C (I) 1.2 : 1
13 1978 S/L Wheat Adeq. (R) inv. T/C (IV) : t.d. V/C (I) no diff.
14 1978 S/L Lupin Adeq. (R) inv. T/C (IV) : t.d. V/C (I) no diff.
15 1979 S/L Wheat Adeq. (R) inv. T/C (IV) : t.d. VN (I) no diff.
16 1979 S/L Wheat Dry (R) inv. T/C (IV) : t.d. V/C (I) no diff.
17 1979 S/L Wheat Adeq. (R) inv. T/C (IV) : t.d. V/C (I) no diff.
18 1979 S/L Wheat Adeq. (R) inv. T/C (IV) : t.d. V/C (I) no diff.
19 1985 S/L Barley Adeq. (NR) inv. T/C (IV) : t.d. V/C (I) no diff.
20 1985 S/L Barley Adeq. (NR) inv. T/C (IV) : t.d. V/C (I) no diff.
21 1985 S/L Barley V. wet (NR) p.t. U/C (III) : p.p. U/C (I) 4.2 : 1
22 1985 S/L Barley V. wet (NR) inv. T/C (IV) : t.d. V/C (I) 1.7 : 1
23 1985 S/L Barley V. wet (NR) t.d. V/C (I) : inv. T/C (IV) 1.6 : 1
24 1985 S/L Barley V. wet (NR) t.d. V/C (I) : inv. T/C (IV) 1.2 : 1
25 1985 S/L Barley V. wet (R) inv. T/C (IV) : t.d. V/C (I) 4.4 : 1
26 1985 S/L Barley V. wet (R) inv. T/C (IV) : t.d. V/C (I) 2.9 : 1
27 1985 S/L Barley V. wet (R) inv. T/C (IV) : t.d. V/C (I) 2.7 : 1
28 1985 S/L Barley V. wet (R) inv. T/C (IV) : t.d. V/C (I) 2.5 : 1
29 1985 S/L Barley V. wet (R) inv. T/C (IV) : t.d. V/C (I) 1.5 : 1
30 1985 S/L Barley V. wet (R) inv. T/C (IV) : t.d. V/C (I) 1.4 : 1
aSoil types: S/L = silt loam; FS/L = fine sandy loam.
bSoil moisture and residue status: V. dry = Very dry; Adeq. = Adequate: V. wet = Very wet.
c(R) = surface residues present; (NR) = no surface residues present; (I), (II), (III) and (IV) = the classes of
cover in each experiment. Drilling and covering treatments: t.d. V = triple disc opener, vertical V-shaped
slot, not covered; t.d. V/C = triple disc opener, vertical V-shaped slot, covered; hoe U = hoe opener,
U-shaped slot, not covered; hoe U/C = hoe opener, U-shaped slot, covered; inv. T = winged opener,
inverted-T-shaped slot, not covered; inv. T/C = winged opener, inverted-T-shaped slot, covered;
p.t. U = power till opener, U-shaped slot, not covered; p.t. U/C = power till opener, U-shaped slot,
covered; p.p. U = simulated punch planter, U-shaped holes, not covered; p.p. U/C = simulated punch
planter, U-shaped holes, covered.
Sources: Experiments 1, 5, 8, 9, 11, 12, 15, 16, 17 and 18 (Choudhary, 1979); Experiments 2, 3, 4 and
10 (Baker, 1976a); Experiment 6 (Baker, 1976b); Experiment 7 (Baker, 1971), Experiments 13 and 14
(Mai, 1978); Experiments 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29 and 30 (Chaudhry, 1985).
Note: In all experiments where the slots were covered, the covering material was the best available as
provided by the shape of the slot and opener action.
Table 5.2. Effects of slot cover on seedling emergence in 30 experiments.
2. Rolling – pressing vertically on the soil
alongside the slot with a roller of some
description.
3. Pressing – selectively pressing on or in
the slot zone itself, including non-vertical
rolling or pressing mainly to obtain seed–soil
contact, but can also include an element of
covering.
4. Scuffing – scraping up loose surface
material from the slot zone and directing it
to fall back into the slot, solely for covering.
5. Deflecting – discretely deflecting soil
from a particular part of the slot, solely for
covering.
6. Tilling – loosening the ground behind
the opener, usually so that it can be more
easily manipulated by one of the other
devices previously listed.
7. Folding – folding soil and/or residue back
from whence it came, solely for covering.
Often two or more of these actions are
combined in one covering/pressing device
or system.
To a casual observer, there might not
seem to be much difference between the
various actions described above. However,
a description of the advantages and disadvantages
of each principle will illustrate
why cover and, to a lesser extent, pressing
are such an important factor in reducing the
risks associated with no-tillage.
Squeezing
Squeezing is the principle applied by many
manufacturers of vertical double disc openers
(see Chapter 4). It usually involves pressing
down with a V-shaped wheel alongside the
slot after its formation in such a manner that
the mass of soil is pushed bodily sideways
without actually loosening it. The aim is to
squeeze the slot closed by moving the soil
back from whence it came. Figure 4.7 illustrates
squeezing wheels behind double disc
openers. The advantages are that such wheels
are simple, require little adjustment and are
not inclined to block with residue.
The disadvantages are that there is
almost as much downforce required on the
pressing wheels as was needed on the
opener to create the slot in the first place,
adding to the weight requirements of the
drill; the pressing action further compacts
the soil next to the seed; its ability to close
the slot is highly dependent on soil plasticity
and moisture content; any useful effect
may be undone quickly if the soil dries and
shrinks after pressing. Slots made in soils
that do not squeeze easily might not be adequately
closed, although with soils of this
nature there is little else that can be done to
remedy the situation. With soils in which
the slot can be squeezed back together,
there is a risk of so tightly trapping the
seeds with compacted soil that emergence
of seedling shoots is restricted.
Rolling
General rolling of a field after drilling is often
undertaken in an attempt to produce some of
the squeezing action described above in a
random manner, without directing the action
to any specific zone. It works best where slot
formation results in considerable hinged
upheaval of the soil such as with hoe openers
and some simple inverted-T-shaped openers.
The vertical forces from the roller tend to
squash any raised ridges of soil downwards
and, to a limited extent, sideways. Since most
of the raised portions of soil will be alongside
the slots, a degree of covering often results,
although, as with squeezing, the final result is
highly dependent on soil moisture content
and plasticity.
Both flat and ringed (‘Cambridge’) rollers
are used. The problem with ringed rollers
is that the points of the rings apply more
pressure than the shoulders. If the point of a
ring happens to coincide with the centre of
a sown row it may help to bury the seed too
deeply or at least it may seal the exit zone so
tightly as to restrict seedling emergence. For
these reasons flat rollers are preferred to
‘Cambridge’ rollers.
The main advantage of rollers is that
they are generally readily available implements
and easy to use, and their downforces
are derived from their own weight
rather than the drill. They also leave a relatively
flat finish to the field, which might be
important at harvesting.
Role of Slot Cover 67
The disadvantages are that covering
must be done as a separate operation and
that much of the loose soil and debris is not
adequately moved sideways into the slot
zone but is instead ‘trampled’ down where
it lies, in which case it might not contribute
to covering at all. This latter disadvantage is
more of a problem with hoe openers than
with simple inverted-T-shaped openers,
because the latter hinge up a flap of soil
rather than bursting it out bodily sideways
in the manner of hoe openers.
Pressing
Pressing is really rolling in a discrete zone
and perhaps at a discrete angle in or on top
of the slot. The slot can be pressed either
after it has been covered by some other
means (e.g. scuffing) or prior to the covering
action. The object of pressing alone is to
effect the covering action and it is particularly
useful with slanted double disc openers.
Pressing in association with another
covering device improves soil–seed contact,
but there is little scientific evidence to
show that this results in an improvement in
seedling emergence under no-tillage except
perhaps by improving the consistency of
seeding depth (Choudhary, 1979; Choudhary
and Baker, 1981a).
Pressing before covering, on the other
hand, has been shown to be of major benefit
with some openers such as hoe and vertical
double discs. Few manufacturers, however,
have seen fit to provide press devices that
act on the seed before covering of the slot.
Figure 5.6 illustrates a ribbed press wheel
designed to press in the base of the slot
while simultaneously rolling on the undisturbed
soil alongside. Figure 5.7 shows a
packing device designed to firm the seed
into the base of the slot at the same time that
covering takes place.
The advantages of pressing are that it
usually involves a wheel (or pair of wheels)
that can double as a depth-control device.
This double function, however, is not easy to
achieve if the press wheel operates in the
base of a slot, since the wheel then registers
on a soil surface that has already been created
by the opener and thus may have little
reference to the true surface of the soil. On
the other hand, pressing before covering
does more to counteract the disadvantages
68 C.J. Baker
Fig. 5.6. A press wheel with central rib, which is designed to press in the base of the slot at the same
time as it locates on the soil surface (from Baker et al., 1996).
of U- and vertical V-shaped slots than any
other known method (Choudhary, 1979;
Choudhary and Baker, 1981a). The effect
seems to be to press the seeds into the undisturbed
soil at the base of the slot so that their
emerging roots do not need to negotiate the
slot wall in order access soil water.
The disadvantages are that pressing
alone is not always a covering action at all.
It is usually done after or before covering
is achieved by some other means, so two
separate mechanisms are necessary. Also,
because pressing after covering is easier to
achieve and the press wheels are able to roll
on the undisturbed soil alongside the slot
and thereby achieve depth control at the
same time, this has become the preferred
option. It does not, however, achieve as
much biologically as pressing before covering
(see also Chapter 6).
Scuffing
Scuffing is probably the easiest and most
effective general slot covering option that can
be performed by a separate machine after
drilling, regardless of the type of drill opener
used. It usually involves a heavy, wide, flexible
harrow of some nature, which is pulled
across the ground, preferably parallel to the
drill slots. The harrow scrapes up the general
loose soil spilled from the slots and other
debris, and pushes this material back over the
slots in a random manner. Its action depends
on the untilled ground between the rows
being able to support the weight of the device
so that it does not cut into the soil and
thereby accumulate excess soil and debris.
Some of the heavy harrows used in no-tillage
are therefore not applicable to tilled soils.
Various harrows have been used, ranging
from chain harrows with the points facing
upwards to avoid gouging seed out of
the slots, truck tyres that have been split
longitudinally with the cut surfaces facing
downwards, oyster nets, heavy chains and
short lengths of railway iron chained
together. Figure 5.8 shows a bar harrow
made of railway iron operating in a friable
soil after a drill with hoe openers (Baker,
1970). Figure 5.9 is a plan of such a harrow,
suitable for a 2.4 m wide drill.
The advantages of harrows are that they
are virtually foolproof to operate, simple and
inexpensive. For many slot shapes created
in damp soils, harrowing is best delayed a
few hours to allow some dry crumbs to
develop, which can then be scraped up as
friable covering material. A separate harrow
is ideal for such situations.
The disadvantages are that if no crumb
is formed when drilling, for example, with
vertical double disc openers operating in a
damp soil, even harrows will be ineffective
to provide cover. Their use constitutes
another operation, although, if a time delay
is not appropriate, they can be attached
behind the drill; and with severe residue
they can become blocked.
A variation of scuffing and rolling is provided
by spiral-caged rollers, as shown in
Fig. 5.10. These devices combine the pressing
effect of a roller with the scuffing effect of a
harrow, since the spiral nature of the rolling
ribs ensures that some sideways scuffing
takes place as the roller rotates. They are easy
and convenient to use but do not move as
much debris and soil as a true harrow.
Deflecting
With some hoe openers, small deflecting
devices are incorporated on the rear of the
Role of Slot Cover 69
Fig. 5.7. A shank-type opener with packing
device to firm seeds into the base of the slot at the
same time as covering takes place.
opener so as to scrape a small slice of soil
fromthe slot wall and allow it to fall on to the
seed and/or fertilizer. One of the purposes of
doing this has been to attempt to get a soil
covering over a deposit of fertilizer in the
base of the slot before seed is deposited on
top of the soil, thus separating them vertically
within the slot (Hyde et al., 1979, 1987).
70 C.J. Baker
Fig. 5.8. A simple bar harrow for covering no-tillage slots (from Baker et al., 1996).
Fig. 5.9. Plan for a simple
bar covering harrow (from
Baker, 1970).
Unfortunately, the function of any fixed
device, such as an internal scraper of this
nature, is highly dependent on the position
of the scraper relative to the slot walls.
Since the slot walls themselves are never in
exactly the same place in two different
soils, or even in the same soil at different
moisture contents or operating speeds,
either the scrapers have to be manually
adjusted for each new soil condition or the
functional ability of the device will vary
quite widely with the conditions. While
successful deflectors facilitate vertical
separation of seed and fertilizer in the slot,
stationary scrapers often collect residue and
cause blockages.
Tilling
Because of the difficulty of moving soil that
has been squeezed sideways back in the
opposite direction, some openers attempt
to loosen the soil alongside the slot with
the aid of spiked wheels or discs. Often,
spiked discs are arranged alongside angled
press wheels so that the loosening and
reverse-squeezing actions are combined
into one, such as those shown in Fig. 5.11.
The advantages are that the soil is more
easily moved, and, because it is in a loosened
state, the risk of further compaction, particularly
over the seedling emergence zone, is
reduced. The disadvantage is that any disturbance
of this nature partly destroys the integrity
of the residue and soil layering, and at
best results in a random mixture of soil and
residue as the covering medium.
Folding
Folding of material back over a slot presupposes
that a horizontal slot has been
created in a manner that hinged the original
covering material up in the first place.
Alternatively, the slot may have been created
so that the original covering material
has been displaced bodily sideways without
inversion and mixing, in a manner that
allows it to be retrieved and replaced as if it
had not been moved in the first place.
Realistically, this applies only to
inverted-T-shaped horizontal slots, slanted
Role of Slot Cover 71
Fig. 5.10. A spiral-caged roller for covering no-tillage slots.
double disc openers and perhaps those
angled dished disc openers that have a
positive tilt angle. Even with inverted-T
openers, the folding feature is more a function
of how the slot is created than the
action of the covering device. For example,
the uplifted flaps of most inverted-
T-shaped slots, when created in pasture,
can be folded down again either by a scuffing
harrow or by press wheels. Press wheels
are more tolerant of different soil and pasture
conditions, and are more predictable
than scuffing harrows, but they need to be
angled to combine the folding and pressing
functions.
In non-pasture soils such as arable soils
with loose or lying residue, the folding
function can only be realistically performed
by press wheels. It is even possible to refine
the folding function sufficiently to allow
stratified soil layers, e.g. a thin dry dust
mulch that overlies more moist soil, to
be replaced more or less in the same order
that they were in before passage of the
opener. Figure 4.27 and 4.29 show a pair of
folding wheels, which also function as
depth-gauging wheels, on a disc version of a
winged opener.
The advantages of folding are that the
covering function is predictable and reliable
and usually does not require adjustment of
opener components to cope with different
soil or residue conditions. It can also result
in complete mulch and soil cover (Class IV),
so long as there was a mulch covering the
soil in the first place.
The disadvantages are that excess pressure
from press wheels on a damp pasture
flap might close the slot so tightly as to make
it difficult for seedlings to emerge. Since
this is a function of the downforce applied
to the openers, it is easily adjusted in the
normal course of setting up a no-tillage drill.
Summary of the Role of Slot Cover
1. There are four distinguishable classes
of slot covers, ranging from no cover (Class
I), loose soil (Class II), soil and a small
amount of mulch or residue (Class III), to
complete (greater than 70%) soil and mulch
(Class IV).
2. In Class III, the small amount of mulch
or residue in the covering medium may be
72 C.J. Baker
Fig. 5.11. A pair of combined spiked discs and angled press wheels for covering no-tillage slots
(from Baker et al., 1996).
either in intermittent clumps (Class IIIa) or
a thoroughly mixed combination of residue
and soil (Class IIIb).
3. Class I–IV covers are ranked in ascending
order of their abilities to retain slot
water vapour.
4. The benefits of covering in terms of
seedling emergence are ranked in ascending
order of Classes I–IV.
5. Principles of covering slots and/or
obtaining soil–seed contact involve squeezing,
rolling, pressing, scuffing, deflecting
and/or folding soil and/or mulch.
6. Some covering methods involve separate
operations and machines that are used
after drilling, in which case the weather
and soil plasticity after seeding become
important.
7. Other covering methods involve simultaneous
functions by the openers themselves,
in which case the nature and speed of slot
formation become important.
8. Vertical double disc and triple disc furrow
openers and punch planters usually
produce Class I or II cover.
9. Slanted double and single disc openers
and winged openers are capable of producing
Class IV cover.
10. Hoe, angled vertical flat disc and angled
vertical dished disc openers tend to produce
Class II or IIIa cover, depending on the
speed of travel.
11. Power till openers tend to produce
Class IIIb cover, regardless of speed.
12. Angled dished disc openers sometimes
produce Class IV cover at slow speeds.
13. The disc versions of winged openers
are designed to produce Class IV cover
regardless of speed, soil moisture conditions
or residue conditions.
Role of Slot Cover 73
6 Drilling into Dry Soils
C. John Baker
A dry untilled soil has more potential to
germinate seeds and allow seedlings to emerge
than a dry tilled soil; but very few no-tillage
openers are capable of harnessing that potential.
Most of the world’s agriculture involves
growing plants in soils that become dry at
some point in their growing cycles. If farmers
could predict exactly when the soil
was going to become dry, they would plan
accordingly. In many climates an approximate
idea of the onset of rain allows farmers
to match the planting of crops to expected
weather patterns. These matchups, however,
are seldom accurate to better than a
few weeks, if that.
When sowing seeds into untilled soils,
a matter of a few days either way may make
the difference between successful crop
establishment or failure. This is not to say
that untilled soils are less forgiving than
tilled soils; indeed, most have the potential
to be more forgiving. The problem is that
most people have not yet learned how to
harness that tolerance to their advantage.
With little guarantee that it will rain on
a particular day after drilling, farmers are
unlikely to attempt to drill seed into an
already dry soil. On the other hand, if a
farmer drills seed into a soil that appears
to have adequate moisture but then finds
the next week dominated by hot dry winds,
what had been an optimum environment
for seeds may soon become a hostile
environment.
None the less, so long as there is sufficient
weight for penetration of the drill
openers and sufficient energy to pull the
machine through the soil, it is possible to
operate a no-tillage drill in a dry soil. This
contrasts with wet soils (see Chapter 7),
where operation of machinery is often
simply not possible.
How Soils Lose Moisture
To understand the tolerance of untilled
soils to dry weather, it is necessary to distinguish
between an untilled soil that is
covered with a mulch and an untilled soil
that has a bare surface. It is also important
to compare the ways in which tilled and
untilled soils transport water to the surface
for evaporation.
A tilled soil will lose moisture more
rapidly than an untilled soil, at least initially.
But because of the increased porosity
of tilled soils, the loss of moisture from the
upper zones will not be quickly replenished
from deeper zones. The capillary rise of
water is poor through the large voids and
pores that result from tillage.
© FAO and CAB International 2007. No-tillage Seeding and Conservation
74 Agriculture, 2nd edn. (eds C.J. Baker and K.E. Saxton)
Because of this, a dry layer may be
formed at the top of tilled soils. In some climates
a dry dust mulch layer is deliberately
formed by repeatedly tilling the surface
layer of soil until it becomes a super-dry
dust with very low moisture and thermal
conductivities. The rationale behind such a
practice is that, in the absence of any other
form of surface mulch, there is a net saving
in moisture loss by sacrificing a small
amount of water to form a ‘dust mulch’ in the
interest of conserving the greater amount of
water lying beneath it.
An untilled soil, on the other hand,
will usually have a well-developed capillary
system from the surface to some significant
depth, which acts as a continuous
‘wick’, transporting water upwards during
periods of drying at the surface. This internal
transport system will become more
effective with time as soil structure improves.
Thus, while the initial loss of moisture will
be slower from the surface of a bare untilled
soil than from a tilled soil because the
surface is smoother and therefore does not
create as much air turbulence or allow air to
enter as easily, it may continue supplying
water to the surface for evaporation for a
much longer time than a tilled soil that is
covered with a dust mulch. This, then, is
where the presence of an organic residue
mulch and the action of the drill openers
that operate in an untilled soil become
important.
The Role of Vapour-phase Soil Water
All soils contain both liquid-phase water
and vapour-phase water in the form of
humidity. The equilibrium relative humidity
of the pore spaces between the particles
of undisturbed soil is virtually 100% at
all liquid moisture levels down to permanent
wilting point (Scotter, 1976). The permanent
wilting point (PWP) is the point
where the soil is considered too dry to sustain
most plant life. The status of liquid soil
water is often expressed as the tension
by which water films are held by the soil
particles. At PWP this tension is –15 bar.
The important point is that plants wilt and
die at PWP and will not recover if watered
again. However, it is important to remember
that, even at that moisture content, the soil
macropores contain 99.8% relative humidity.
Like hair on the skin of an animal, an
organic mulch traps a layer of still air close
to the soil surface, which slows down the
exchange of water vapour between the soil
and the atmosphere. Most importantly, the
humidity within that mulch layer will remain
much higher than the atmosphere above it,
unless, of course, it is raining or the atmosphere
is at a high humidity anyway.
On a hot, dry day, for example, if one
were to take a rapid-response humidity
probe and carefully slide the probe under a
single large leaf lying on bare untilled soil
without moving the leaf, there would be a
noticeable rise in the humidity reading as
the probe moved under the leaf and then a
drop when it was removed. The same thing
would happen under a piece of plastic or
paper. This demonstrates that a localized
high-humidity zone is possible under a
mulch at the soil surface. This mulch zone
can be quite small in area and unaffected by
another un-mulched zone nearby that has a
much lower humidity. This is a very important
phenomenon and is one of the major
differences between no-tillage openers.
Every farmer in the world can recognize
whether or not a tilled soil has sufficient
liquid-phase water for germination.
The judgement is usually made on the basis
of the colour of the soil – darker-coloured
soil is wetter – or the temperature of the
soil – colder soil is wetter.
Soil humidity is rarely accounted for in
a tilled soil. Nor should it be. Unless the
soil humidity is at least 90%, germination
will mainly occur through uptake (imbibition)
of liquid-phase water from the soil by
the seed (Martin and Thrailkill, 1993;
Wuest, 2002). The humidity in the surface
layers of a tilled soil is likely to approach
90% only on a very humid day or immediately
after rain. As will be explained
below, the humidity in the drilled slot of an
untilled soil is even more important than in
the general soil matrix (Choudhary, 1979;
Choudhary and Baker, 1981a, b).
Drilling into Dry Soils 75
Figure 6.1 illustrates what generally
occurs when seeds are drilled into dry untilled
soils with vertical double disc openers
(V-shaped slot, Class I cover); hoe openers
(U-shaped slot, Class II or III cover); and
winged openers (inverted-T-shaped slot,
Class IV cover). The following explanations
are relevant for each line on Fig. 6.1.
Germination
Germination can occur from uptake of
either liquid-phase water or vapour-phase
water (humidity), or both. For liquid-phase
water uptake to occur the seed must have
physical contact with water-bearing soil by
adequate soil–seed contact.
When seed is wedged in the base of a
V-shaped slot (vertical or slanted) in a dry
soil, the transfer of water from the soil to the
seed is generally adequate, even though the
contact zones with each wall of the slot may
be relatively small (Fig. 6.2). The smooth,
and often compacted, slot walls are a ready
source of liquid-phase water, which is otherwise
scarce in a dry soil. Thus germination
within a V-shaped slot in a dry soil (Class I
cover) can be ‘good’.
With U-shaped slots, there is usually
more loose soil within the slot, which also
has a broader base for the seed to lie upon
(Fig. 6.3). These two factors cause poor
transfer of scarce liquid-phase moisture to
the seed. Even when loose soil covers the
slot and seed, there is little liquid-phase
moisture in this covering medium because
of its loose nature. It remains dry and acts in
76 C.J. Baker
Fig. 6.1. Summary of the responses of
contrasting no-tillage slot shapes to dry
soil conditions. (✓ = good, X = poor.)
Fig. 6.2. The position a seed takes in a vertical
V-shaped no-tillage slot.
Fig. 6.3. The position a seed takes in a
U-shaped no-tillage slot.
a similar manner to a dust mulch, as described
above. Thus germination within a
U-shaped slot in a dry soil (Class II or III
cover) is often ‘poor’.
With inverted-T-shaped slots, the
supply of liquid-phase water to the seed is
little different from that with U-shaped
slots (Fig. 6.4). The Class IV cover, however,
results in the seed being surrounded by
vapour-phase water of 90–100% humidity
(see Chapter 4). The seeds take a little longer
to germinate than where liquid-phase
water is available, but eventually a high
germination count results. Thus germination
within an inverted-T-shaped slot in a
dry soil (Class IV cover) is usually ‘good’.
Subsurface Survival
The most overlooked and under-studied
stage of development of no-tilled seedlings
is the time between germination and when
the juvenile plants finally emerge from the
soil. All of this period is spent beneath the
soil. To remain alive the seedlings derive
nutrients from their seed reserves and moisture
through the embryonic roots, which
appear at the time of germination.
These pre-emerged plants will not have
developed the ability to photosynthesize
food and energy from the sun’s rays. There
is only a limited need for them to draw
water from the dry soil while they are
beneath the surface, because it is mainly the
sun that stimulates transpiration from plants.
The subsurface seedlings, however, do
respire (breathe), consuming moisture, and
there may be subsurface water loss where
the soil humidity, and therefore water vapour
pressure, is lower than the corresponding
water vapour pressure within the embryonic
plants, which results in a diffusion loss
through the cell walls.
Together with respiration, the end result
is a tendency for subsurface seedlings to
desiccate (dry out) unless they have an
available source of soil water. With vertical
V-shaped slots (Class I cover), many of the
new seedlings become desiccated and die.
Often they see sunlight very soon after germination
because of the absence of covering
material in the slot. But, even with Class II
cover (loose soil), they may still die. The
reason often is that the embryonic roots have
to negotiate and penetrate the compacted
slot walls before they can access liquidphase
water from the surrounding soil.
Since the slot walls are nearly vertical
and there is little resistance against which
the roots can base penetration forces, other
than the weight of the seed, the roots tend to
have difficulty penetrating the slot walls
and instead spread sideways along the slot.
The result is that seedlings after germination
receive a poor water supply. Seedlings
cannot stand the strong desiccation demand
from a soil humidity that usually, at best,
remains in the 60–80% range in vertical
V-shaped slots. Therefore, many subsurface
seedlings die before emergence in a vertical
V-shaped slot in a dry soil.
It is useful to contrast this situation
with a fully tilled dry soil. In a tilled dry
soil, seeds are placed in a loose and friable
medium. First, this medium probably does
not transport enough liquid-phase water to
the seed to bring about germination. But,
even for those seeds that do germinate, there
is no compacted slot wall for embryonic
roots to penetrate. So subsurface seedling
Drilling into Dry Soils 77
Fig. 6.4. The seed position in an inverted-
T-shaped no-tillage slot.
deaths in tilled soils are rare, similar to
U-shaped no-tillage slots.
With U-shaped slots (Class II or III
cover), although germination is often poor,
the roots of those seedlings that do germinate
have less trouble penetrating the uncompacted
and broader base of the slots. If the
slot can be covered to Class II or Class III
standard, i.e. at least loose soil or a mixture
of soil and residue, the likelihood of desiccation
of subsurface seedlings is also
reduced. Humidity is likely to remain in the
70–90% range. The result in U-shaped slots
in a dry soil is that a reasonable percentage
of the subsurface seedlings survive, although
there may not be many that germinate until
rain (or even dew) arrives, which means that
seedling emergence may be spread over a
long time.
Figures 6.5 and 6.6 show four wheat
plants that were extracted from dry no-tillage
plots in Australia. In Fig. 6.5, the plants are
oriented so that the slot is running in the
same direction as the wire fence (i.e. across
the field of vision). The two plants on the
left were sown with a vertical double disc
opener (V-shaped slot) and the two on the
right were sown with a wide, hoe-type
opener (U-shaped slot). Root development
along each of the rows is approximately
equal for all four plants (i.e. for both slots).
In Fig. 6.6, all four plants have been
rotated 90° and are now oriented with the
drill rows running towards the camera.
Clearly the roots of the plants on the left
(vertical V-shaped slot) have hardly moved
sideways out of the slot at all, but have
stayed essentially within the slot walls.
The roots of the plants on the right (wide
U-shaped slot), on the other hand, have
spread about as much sideways as they had
lengthwise (Fig. 6.5). This illustrates the
difficulty that young (and even, in this case,
mature) roots have in penetrating the
slot walls of some vertical V-shaped slots,
compared with U-shaped slots.
With inverted-T-shaped slots (Class IV
cover), humidity usually remains in the
90–100% range because of the residuecovered
slot. While this will result in high
(if sometimes slow) counts of germination,
its most important function is that it removes
most of the desiccation or transpiration stress
from the subsurface seedlings, with the
result that their survival rate is also high.
Embryonic root exploration out of the
slot zone is no more restricted with inverted-
T-shaped slots than with U-shaped slots.
78 C.J. Baker
Fig. 6.5. Wheat plants from a no-tilled crop in New South Wales, Australia; slot direction is parallel to
the fence (from Baker et al., 1996).
The combined result is that, with inverted-
T-shaped slots in a dry soil, most of the
subsurface seedlings survive, leading to
rapid and consistent seedling emergence.
Figure 6.7 illustrates the relative rates
of humidity loss from the three contrasting
slot shapes (Choudhary and Baker, 1994).
Scientists in New Zealand tried covering
vertical V-shaped slots with strips of
plastic to artificially trap water vapour in
the otherwise open slots and create artificial
Class IV cover (Choudhary, 1979). The
humidity increased, but fungal growth soon
also became evident in the slots, probably
indicating that air circulation had been
reduced. Therefore, nature had the perfect
covering medium in the form of organic
mulch and residue. Mulch breathes, as well
Drilling into Dry Soils 79
Fig. 6.6. Wheat plants from a no-tilled crop in New South Wales, Australia; slot direction is towards the
camera (from Baker et al., 1996).
Fig. 6.7. The relative
rates of loss of soil
humidity from V-, U- and
inverted-T-shaped
no-tillage slots (from
Carter, 1994).
as trapping humidity. Plastic does not
breathe, even if it traps humidity, and it is
quite impractical to cover every slot drilled
with plastic strips.
It is little wonder, therefore, that deciduous
trees flower, set seed and drop their
seeds to the ground before they drop their
leaves. Nature’s intention seems to have
been to cover the seeds with mulch.
Seedling Emergence
The more Xs in the total for a slot in Fig. 6.1,
the less effective that slot is at promoting
seedling emergence from a dry soil. Conversely,
the more ✓s in the total, the better
the slot.
In summary, the order of ranking with
regard to dry soils is:
1. Inverted-T-shaped slots – Class IV
cover – excellent germination, excellent
survival and thus excellent emergence.
2. U-shaped slots – Class II or III cover –
poor germination, adequate survival and
thus substandard emergence.
3. Vertical V-shaped slots – Class I or II
cover – excellent germination, poor survival
and thus poor emergence.
Table 6.1 (Choudhary, 1979) lists typical
patterns of wheat (Triticum aestivum) seed
and seedling responses to the three slot
shapes in dry soils. These results illustrate
the separate mechanisms of failure of vertical
V- and U-shaped slots, i.e. subsurface
seedling mortality and germination failure,
respectively.
With vertical V-shaped slots, seedling
emergence was poor (27%), although germination
had been reasonably good. Only 9%
of the seeds failed to germinate, the same as
for the inverted-T-shaped slot. On the other
hand, a high percentage (64%) of these
germinated seedlings remained un-emerged
beneath the soil in the vertical V-shaped
slots, and most of them died.
With U-shaped slots, although a higher
percentage (51%) emerged than with
V-shaped slots, 23% of the seeds had not
germinated in the first place. For those that
did germinate, subsurface seedling survival
was reasonably good. Only 26% of the seedlings
remained un-emerged beneath the soil,
similar to the inverted-T-shaped slots (27%).
The distinguishing feature of the
inverted-T-shaped slots was that 64% of the
seeds germinated and emerged. In addition,
27% germinated and remained alive beneath
the soil, awaiting rain. Only 9% did not
germinate in the first place.
Figure 6.8 shows typical seedling
emergence patterns of wheat, no-tilled into
a dry soil under controlled dry conditions
(Baker, 1976b). Clearly the seeds sown in
the inverted-T-shaped slots emerged in much
greater numbers (78%) than from U- (28%)
or vertical V-shaped slots (26%). There
was a few days’ delay before the seeds in
the inverted-T-shaped slot started to emerge,
possibly because they were taking up
vapour-phase water rather than the liquidphase
water that the other two slots were
supplying; but thereafter the emergence rate
was very rapid compared with the other
two slot shapes.
80 C.J. Baker
Double disc opener
Vertical V-shaped slot
Class I cover
Hoe opener
U-shaped slot
Class II cover
Winged opener
Inverted-T-shaped slot
Class IV cover
Seedling emergence 27% 51% 64%
Germinated seeds that
had failed to emerge
64% 26% 27%
Un-germinated seeds 9% 23% 9%
Total seed pool 100% 100% 100%
Table 6.1. Wheat seed and seedling responses to no-tillage openers and slot shapes in a dry soil.
This phenomenon is also illustrated in
Fig. 6.9, which shows field seedling emergence
patterns of peas in a dry soil in Oregon,
USA (Wilkins et al., 1992). Vertical V-, Uand
inverted-T-shaped slots were used, which
were represented by ‘double disc’, ‘striptill’
and ‘cross-slot’ openers, respectively.
Emergence from the U-shaped slots was
spread over a 2–3-day period and reached a
maximum of 65%, 5% better than V-shaped
Drilling into Dry Soils 81
Fig. 6.8. Wheat seedling
emergence patterns from
V- (——), U- (- - - -) and
inverted-T-shaped (.....) no-tillage
slots in a dry soil (Baker, 1976b).
Fig. 6.9. Pea seedling
emergence patterns from
V-, U- and inverted-T-shaped
no-tillage slots in a dry soil (from
Wilkins et al., 1992).
slots, which otherwise spread their emergence
pattern over the same length of time.
Seedlings in the inverted-T-shaped slots
did not start to emerge until 1–2 days after
the other two slots, but then almost all of
the plants came up in a single day and
attained a total of 90% emergence. The
evenness and consistency of emergence
shown by the inverted-T-shaped slot has
important consequences for eventual crop
maturity and yield; and, of course, 90%
emergence contributes to greater yields
than 50–65% emergence.
A further experiment by Choudhary
(1979), shown in Table 6.2, illustrates the
effectiveness of the three slot shapes in a
dry soil compared with the same soil when
rewetted. The most noticeable effect was
that both the vertical V- and U-shaped slots
responded positively when the moisture
status of the soil was raised. Their seedling
emergence counts increased by fourfold
and twofold, respectively. The inverted-
T-shaped slots increased by only 9%
because their dry soil counts were reasonably
high in the first place.
As in Table 6.1, vertical V-shaped slots
had a high count (72%) of un-emerged seedlings
in the dry soil, which decreased only
slightly (to 58%) in more moist conditions,
indicating that many seedlings had already
died. U-shaped slots had a relatively high
count (47%) of un-germinated seeds in the
dry soil, which was later eliminated altogether
(to 0%) when the soil moisture level was
raised, indicating that all the un-germinated
seeds had remained viable. This illustrates
again that the causes of failure in a dry soil
for vertical V- and U-shaped slots are quite
different from one another. In the case of vertical
V-shaped slots, it is failure of seedlings
to survive beneath the soil, while, in
U-shaped slots, it is failure of seeds to germinate
in the first place. With inverted-Tshaped
slots, most of the seeds had
germinated even in the dry soil and about
the same number as for U-shaped slots
remained un-germinated beneath the soil.
The question arises as to what happens
to the subsurface seedlings that have not
emerged from a dry soil in field situations.
The fate of such seedlings depends on two
things: (i) how soon after drilling rain
occurs; and (ii) how effectively the slot
maintains the subsurface seedlings in
a viable state awaiting that rain. The high
humidity of inverted-T-shaped slots will
maintain seedlings in a viable state for
much longer than U-shaped slots, which are
themselves better in this respect than
vertical V-shaped slots. In the laboratory,
germinated wheat seedlings have remained
viable beneath a dry soil with Class IV cover
for 3 weeks. In one field situation, however,
on a very light soil of volcanic ash origin,
ryegrass (Lolium perenne) seedlings survived
beneath the surface of Class IV cover
(inverted-T-shaped slot) for 8 weeks before
rain finally fell, at which time they emerged,
apparently none the worse for having
spent that amount of time beneath the soil
(S.J. Barr, 1990, unpublished data).
Provided that rain or irrigation occurs
before the subsurface seedlings have died
82 C.J. Baker
Double disc opener
Vertical V-shaped slot
Class I cover
Hoe opener
U-shaped slot
Class II cover
Winged opener
Inverted-T-shaped slot
Class IV cover
Moist Dry Moist Dry Moist Dry
Seedling emergence 42% 10% 70% 31% 68% 59%
Germinated seeds that
had failed to emerge
58% 72% 30% 22% 32% 23%
Un-germinated seeds 0% 18% 0% 47% 0% 18%
Total seed pool 100% 100% 100% 100% 100% 100%
Table 6.2. Wheat seed and seedling responses to no-tillage openers in a dry soil and soil of adequate
moisture.
from desiccation, it might be possible to get
a positive response to watering after drilling
with both vertical V- and U-shaped slots.
By irrigating 22 days after a dry soil had
been drilled under no-tillage, Baker (1976a)
obtained an increase in emergence counts
from 21% to 75% with V-shaped slots, and
from 38% to 92% with U-shaped slots.
With inverted-T-shaped slots, the increase
was much more modest, from 78% to 86%,
again because seedling emergence had
already been high when the soil was in a
dry state prior to irrigation.
The Effects of Pressing
One of the most common practices in tilled
seedbeds is to press on the rows after covering.
The practice seeks to improve seed–soil
contact and attract water to the seed by
capillary action. Undoubtedly it improves
seed–soil contact but its function in attracting
water to the seed is dubious. Cross
(1959) demonstrated that, in a dry soil, consolidation
under the seed was more important
than consolidation above the seed, and
there has always been doubt about the real
benefits of pressing on tilled soils anyway.
It seems that pressing after covering
in an untilled soil is of even less benefit.
Choudhary (1979) and Choudhary and Baker
(1981b) conducted experiments that compared
pressing on the soil after covering
with covering alone and pressing on the
seed before covering. They found no benefit
at all for pressing on the covered slots in a
dry soil. Most importantly, they found substantial
benefits from pressing on the seeds
in the slot before covering, but only in vertical
V- and U-shaped slots. With inverted-
T-shaped slots, seedling emergence was
already high in the absence of pressing,
so there was little improvement from any
subsequent pressing action.
In U-shaped slots, pressing the seed
into the base of the slot ensures that the seed
has good contact with the water-bearing soil.
Since there is usually insufficient water
vapour in U-shaped slots to germinate the
seed and seed–soil contact is otherwise poor
for liquid water uptake, pushing the seed
into the undisturbed soil ensures that at
least liquid water uptake is available in
much the same way as for V-shaped slots, as
illustrated in Fig. 6.10.
In vertical V-shaped slots, pressing the
seed into the base of the slot has a different
effect. Embedding the seed directly into the
undisturbed soil ensures that the radicle
(first root) emerges directly into soil, from
which it will derive its all-important water
uptake (Fig. 6.11), thus bypassing the stress
period when embryonic roots otherwise
attempt to penetrate the slot wall. Thus,
pressing on the seeds prior to covering of
Drilling into Dry Soils 83
Fig. 6.10. The position of seeds after pressing in
the base of a U-shaped no-tillage slot.
Fig. 6.11. The position of seeds after pressing in
the base of a V-shaped no-tillage slot.
both U- and vertical V-shaped slots has
significant benefit in terms of improving
seedling emergence from a dry soil.
Field Experience
In New Zealand a field experiment sought to
drill with three contrasting no-tillage opener
types each second Monday for 6 summer
months regardless of soil or weather conditions
in order to gauge how often limiting
conditions occurred in that region (Choudhary
and Baker, 1982). By chance, on one occasion
the soil moisture level was close to
the permanent wilting point. On this occasion,
inverted-T-shaped slots obtained 50%
emergence of wheat, whereas U- and Vshaped
slots in the same soil produced virtually
no seedling emergence. It is doubtful
if any seeds would have emerged from a
tilled soil at or near PWP either.
It is little wonder, therefore, that repeat
surveys of operators of drills with openers
that created inverted-T-shaped slots in New
Zealand, covering some 40,000 hectares per
year in both spring and autumn sowing
(Baker et al., 2001), revealed a 99% success
rating for the drilling process and technology.
Summary of Drilling into Dry Soils
1. The descending ranking of biological
performance of slot shapes in dry soils is
inverted-T-, followed by U-, then vertical
V-shaped slots.
2. The descending ranking of effectiveness
of slot cover in dry soils is Class IV to
Class I.
3. Inverted-T-shaped slots trap water
vapour within the slot, which germinates
seeds as well as sustaining subsurface
seedlings.
4. The predominant cause of failure of
vertical V-shaped slots is subsurface
desiccation of seedlings, not germination
failure.
5. The predominant cause of failure of
U-shaped slots is germination failure.
6. Pressing on the soil after covering the
seed has negligible effect with any slot shape.
7. Pressing on the seeds in V- and
U-shaped slots before covering improves
their performance noticeably.
8. Surface residues are an important
resource for promoting seedling emergence
from dry soils, provided the openers utilize
them correctly in the covering medium
to trap humidity. Inverted-T- and slanted
V- (but not vertical V-) shaped slots are
most effective.
9. It is possible to obtain more effective
seedling emergence from a dry soil using
no-tillage rather than tillage, provided the
correct technique and equipment are used.
10. With inverted-T-shaped slots, it is possible
to obtain seedling emergence from
untilled soils that are too dry to sustain
effective crop growth.
84 C.J. Baker
7 Drilling into Wet Soils
C. John Baker
The biological ranking of no-tillage opener
performance for wet soils is almost identical
to that for dry soils, but for different reasons.
Unlike dry soils, it is usually impossible to
physically drill into soils that are already
very wet because of limitations in drill
performance, limited traction or excessive
compaction. Thus, in considering wet soil
effects, it is important to distinguish
between two different situations:
1. Drilling into soils that are sufficiently
wet to make them sticky and/or plastic in
nature and yet are still able to be drilled.
2. Drilling into soils that were not excessively
wet at the time of drilling but that
become very wet soon after drilling.
Drilling Wet Soils
The most pressing problem to drill an
already wet soil without plugging (situation
1 above) from an operational point of view
relates to the physical ability of openers.
There are few common principles that distinguish
one opener from another in this
regard. In general, all openers with rotating
components have limitations in wet soils,
especially in wet soils that are also sticky.
The use of subsurface scrapers on some disc
openers will extend their tolerance of wet
soils.
Where an opener employs press or
gauge wheels of the semi-pneumatic (‘zeropressure’)
type, the operational limit of the
whole opener in wet and/or sticky soils
is the limit to which these tyres can continue
to operate without plugging. Semipneumatic
tyres are particularly good at
shedding mud (see Chapter 10), so it is
illogical to expect an opener to handle wet
soils any better than its tyres.
Putting to one side the ability of different
openers to operate without plugging,
there are important biological effects that
also arise as a result of the physical action
of different openers in wet soils. The most
important biological factor is the amount of
compaction, smearing and crusting created
by different openers. Smearing is very localized
compaction within the slot (perhaps
only 1–2 mm thick) and crusting is usually
a smear that has dried hard.
Dixon (1972) illustrated the effects of
vertical double disc openers (V-shaped
slot), simple hoe openers (U-shaped slot)
and simple winged openers (inverted-Tshaped
slot) at different soil moisture contents,
one of which was quite wet (27%)
(Fig. 4.1). Several others have also studied
the tendencies of different openers to
compact the base and side walls of the slot
© FAO and CAB International 2007. No-tillage Seeding in Conservation
Agriculture, 2nd edn. (eds C.J. Baker and K.E. Saxton) 85
(Dixon, 1972; Baker and Mai, 1982b;
Mitchell, 1983). From these studies and
countless field observations, the compaction,
smearing and crusting tendencies of
different openers can be summarized as
follows.
Vertical double (or triple) disc openers
(V-shaped slots)
These have the strongest compaction tendencies
of all no-tillage openers. Compaction
occurs at both the base and side walls
of the slot. They also have a strong smearing
tendency, which is accentuated by the open
slot. Because the smears are open to the elements,
they often dry after passage of the
opener and soon become internal crusts,
which restrict root penetration.
In sticky wet soils, soil clings to the
outside of the discs, which lift soil and seed
from within the slots and deposit them
alongside, thus negating the true V shape of
the slots. Figure 4.5 shows a slot made by a
vertical double disc opener in a sticky
Australian soil. The slot has been severely
disrupted by soil sticking to the disc.
Vertical double or triple disc openers
have a strong tendency to tuck (or hairpin)
residue into the slot, as described in more
detail later. The slot cover is typically Class I.
Slanted double (or triple) disc openers
(slanted V-shaped slots)
These are somewhat less likely to compact
the seed zone but only if the seeding opener
is preceded by another double or triple disc
fertilizer opener slanted in the opposite
direction. Because of the slant, the upper
side of the slot wall created by the first
opener actually heaves the soil upwards
and loosens it somewhat. Although the second
slanted opener actually compacts the
soil beneath it more than if it had been operating
in a vertical position, the pre-loosening
of this soil by the first opener, which normally
operates somewhat deeper than the
second opener, negates most of the harmful
effects.
Where a slanted double or triple disc
opener is not preceded by a similar opener
slanted in the opposite direction, the compaction
beneath the opener will be greater
than if the opener had been operating vertically.
Compaction above the opener will be
relieved, but loosening will have little effect
on root penetration of seedlings, although it
will improve the moisture-retention properties
of the slot, which in turn will reduce
the risk of the internal surfaces of the slot
drying to form crusts.
Slanted double or triple disc openers
otherwise have all of the same problems
associated with their vertical counterparts,
including hairpinning of residue into the
slot zone and a tendency for sticky soils to
cling to the outside of the disc and disrupt
the integrity of the slot shape. The slot
cover varies from Class II to Class IV.
Vertical angled flat (or dished) disc
openers (U-shaped slots)
These have little or no compaction tendencies
and little or no tendency to smear or lift
soil in sticky conditions. Covering of the
slots may be difficult, however, in continued
wet weather, for the same reasons later
outlined for hoe-type openers. Angled disc
openers also tend to tuck (or hairpin) residue
into the slot (see below). The slot cover
is typically Class I or II.
Hoe-type openers (U-shaped slots)
These usually result in little compaction,
unless they are of a design that has a large
flat base, in which case they may compact
the base of the slot, but not the side walls. In
wet soils they almost invariably create
smears on the base and side walls of the
slot. These become important if the slot
remains uncovered after drilling and the
smears are allowed to dry to form crusts.
Covering is a particular problem. Hoe
openers rely on the covering device collecting
up the spilled soil alongside the slot and
brushing it back over the slot as covering
material. In a wet soil, such covering material
86 C.J. Baker
is unlikely to become crumbly, so the slot is
difficult to cover at all, encouraging eventual
crust formation.
If covering needs to be a separate operation,
its effectiveness depends on allowing
sufficient drying for crumb to form in the
debris alongside the slot, but not so much
drying as to allow any smears within the
slot to become crusts. Thus, although hoe
openers can be used successfully in wet
soils, they require a high level of skill to
overcome their shortcomings. Hoe openers
can experience problems in sticky soils if
soil accumulates on the sides of the opener
and changes its shape and dimensions. The
slot cover is typically Class I.
Power till openers (U-shaped slots)
These mostly compact the base of the slot
and may smear that zone as well. This
smearing and compaction, however, are
seldom severe and, because the soil is not
often spilled completely out of the slot, the
smears are usually not at risk of becoming
crusts unless a very severe drying period
follows drilling.
Power till openers mechanically aerate
the soil more than any other opener type,
which can be beneficial in wet soils with
low residue levels and only small populations
of earthworms. On the other hand,
some power till openers may become totally
inoperable in sticky wet soils due to ‘plugging’
between the cutting blades. The slot
cover is typically Class IIIb.
Winged openers
(inverted-T-shaped slots)
These smear the base of the slot about as
much as most hoe openers but result in
minimal compaction. Like power till openers,
winged openers have an advantage in
that they either close the slot themselves or
make closure by a separate device easy and
not dependent on moisture or weather.
Thus, smears do not become crusts and
therefore do not restrict root growth.
Winged openers handle sticky soils
reasonably well. The disc version of the
opener uses subsurface scrapers to overcome
the tendency of sticky soils to cling to
the disc. Figure 7.1 shows the benefits of
scrapers used on a winged opener in the
same sticky Australian soil as depicted in
Fig. 4.5. The integrity of the slot and the residue
cover have remained intact. The slot
cover is typically Class IV.
Figures 7.2 and 7.3 show sections of
soil in the side walls of two no-tillage slots
photographed with an electron microscope
(Mai, 1978). The lighter grey areas in the
uncompacted soil in Fig. 7.2 are natural
voids and macropores. In addition, much
organic matter in the form of roots and
buried residue is visible. In contrast, the
compacted soil in Fig. 7.3 has almost no
macropores and little visible organic matter.
Instead, it contains only a few cracks in
which soil oxygen can circulate. It is obvious
why earthworms prefer soil surrounding
inverted-T-shaped slots to that which
surrounds V-shaped slots.
Soil type is also important in wet-soil
seeding. If a small handful of soil can be
‘ribboned’ by rubbing it between the thumb
and forefinger, it will probably become
smeared by those openers that have smearing
tendencies. In general, sandy soils and
well-structured loamy soils with reasonably
high levels of organic matter seldom take on
smears or become permanently compacted
by passage of no-tillage openers. Many clay
soils take on a smear readily when wet.
Montmorillonitic clays may become sticky
instead. Silty soils lie in between clays and
sands.
Many of the sticky montmorillonite
clays produce good crops because of their
incredible water-holding capacity. They
also have a strong tendency to shrink when
drying. This produces internal cracking,
forming quite deep fissures in the soil.
During the early stages of drying and cracking,
the soil mass breaks itself into smaller
particles by shrinkage, almost as if it had
been tilled. Such soils are said to be
self-mulching. They produce a dilemma for
tillage practices. Because they are so sticky
when wet, they are difficult to work in that
Drilling into Wet Soils 87
state with tillage equipment. But waiting
until they dry and are easier to work risks
sacrificing valuable soil water during the
drying and tillage periods.
No-tillage offers a realistic option for
such soils, since it allows sowing directly
into the untilled soil with minimal disturbance.
This is best done when only a small
88 C.J. Baker
Fig. 7.1. Class IV slot cover remaining intact after passage of a winged opener, equipped with
scrapers (inverted-T-shaped slot), through a damp sticky soil (compare with Fig. 4.5).
Fig. 7.2. Electron-microscopic section of soil from the wall of an inverted-T-shaped slot
(from Baker and Mai, 1982b).
amount of surface drying has occurred.
Avoiding inversion of the deeper, more
moist layers during drilling then becomes
an important function of the no-tillage
openers, both because such inversion
brings up wet soil that sticks to everything
and because it results in unnecessary loss of
soil moisture. This contrasts with continuous
tillage, in which the resistance of soils
to compaction and smearing declines with
time and continuous working. Vehicle traffic
exacerbates the situation, leading to a
cumulative decline in the usefulness of
such soils when they are worked in a wet
state. Since the practice of no-tillage gradually
increases SOM levels and structure
over time, many soils are likely to become
less liable to smear or compact with time
and therefore better able to be drilled when
wet.
Drilled Dry Soils that Become Wet
Drilling dry or moist soils that have yet to
become wet will not create substantive
smearing or compaction problems with any
design of opener. Thus, the differences
between openers reflect the abilities of the
various slot shapes to create microenvironments
that will remain beneficial to
seeds, seedlings and growing plants even
after the soils have subsequently become
wet. The most important criterion is their
effect on the oxygen status of the soil, since
roots breathe, and saturation by water will
otherwise drown both seedlings and beneficial
soil fauna.
Wet soils, especially when they have
not been tilled, have a complex relationship
with seeds. For example, if the soil has not
been tilled for some time and has a reasonable
population of earthworms, the earthworms
will have an important effect on
oxygen diffusion in the seed zone and water
drainage. Their burrowing activity provides
channels for air entry and water exit.
Earthworms also need feeding. They
respond rapidly to the presence or absence
of food supplies. There are several species
of earthworm and each species prefers
to occupy a certain depth range of soil.
Those that feed on surface residues (e.g.
Lumbricus rubellus Hoff and Allolobophora
caliginosa Sav) live near the surface and are
the first to react to excess water on the soil
surface. They also react to the presence or
absence of residues, which comprise their
food supply, even to the extent that their
Drilling into Wet Soils 89
Fig. 7.3. Electron-microscopic section of soil from the wall of a V-shaped slot
(from Baker and Mai, 1982b).
burrowing and casting will reflect the
presence of surface residues only a few
centimetres apart.
In experiments with no-tillage openers
in soils that were to become wet, Chaudhry
(1985) tested the effects of the presence or
absence of surface residues. ‘Residue’ plots
had long, rank ryegrass (Lolium perenne)
growing on them, which was sprayed.
‘Non-residue’ plots had this grass removed
at ground level just before drilling. Within
24 h of mowing, the earthworm populations
in the ‘non-residue’ plots had halved,
presumably as a response to the removal
of their principal food source.
It has also been observed that earthworms
appear to have a preference for the
disturbed slot zone in a soil after drilling, as
opposed to the undisturbed soil alongside,
but only if this slot zone is covered with a
ready source of food (residue) and only if it
is not compacted. Presumably they find
the loosened soil easier to burrow through
and the covering of residue provides an
improved environment and a convenient
food source.
Table 7.1 shows the effects on seedling
emergence of barley (Hordeum vulgare) in
a wet soil by the three common slot shapes
with and without surface residues (Chaudhry,
1985; Chaudhry and Baker, 1988). The table
also shows the numbers of earthworms
recovered from 120 mm diameter × 100 mm
long soil cores centred on the drilled rows.
The index of earthworm activity, measured
as the percentage of the area of ground covered
by earthworm casts, showed similar
trends to the numbers of earthworms counted
in the soil cores. To create very wet conditions
after drilling in this experiment, the
soil was irrigated with 20 mm of simulated
rainfall per day over a 4 h period, for 20 days
(total, 400 mm in 20 days). In a field situation,
such an intensity of repeat rainfall would be
expected to produce supersaturated conditions
and surface puddling in a short time
span. In the free-draining bins used in this
experiment, supersaturation did not occur
but the soil none the less remained above
‘field capacity’ most of the time.
There were three strong trends in the
data of Table 7.1. First, the greatest seedling
emergence was promoted by the surface
broadcast treatment (87%) and inverted-Tshaped
slots created by winged openers
(76%) (no statistical difference). Next were
U-shaped slots created by hoe (65%) and
power till (63%) openers. The vertical
V-shaped slots created by double disc
openers and the U-shaped holes created
by a simulated punch planter performed
poorly (24% and 17% seedling emergence,
respectively).
Secondly, the number of earthworms
found in cores of soil centring on the drilled
rows mirrored very closely the seedling
emergence counts. Most earthworms were
found in the vicinity of the slots created by
the winged (25), hoe (22) and power till (23)
openers, together with surface broadcasting
(22) and perhaps the punch planter (18),
but the vertical double disc opener (9)
performed poorly.
Thirdly, the presence or absence of residues
had a very positive effect on both seedling
emergence and earthworm numbers
with the inverted-T- and some of the
U-shaped slots and holes, but not with
V-shaped slots or with surface broadcasting.
Residues improved seedling emergence
with the inverted-T-shaped slots from 48%
to 76% and earthworm numbers from 13 to
25. The effect on U-shaped slots was not
quite so marked, but residues none the less
improved seedling emergence from 40% to
65% and earthworm numbers from 13 to 22
with the hoe opener.
In contrast, residues actually depressed
seedling emergence with the vertical double
disc openers (from 25% to 17%) and
punch planter (from 17% to 14%), but had
no effect with surface broadcasting or the
power till openers. The latter phenomenon
is not surprising since the power till opener
chopped up the surface residues (and probably
a number of earthworms) and incorporated
them into the soil. With surface
broadcasting, the seeds were left lying on
top of the ground, making them less likely
to be affected by earthworm activity taking
place beneath the surface. Further, because
moisture was not limiting, it is not surprising
that residues on the soil surface had no
direct effect on emergence with broadcasting.
90 C.J. Baker
Drilling into Wet Soils 91
Double disc
opener vertical
V-shaped slot
Class I cover
Hoe opener
U-shaped slot
Class I cover
Winged opener
Inverted-Tshaped
slot
Class IV cover
Power till opener
U-shaped slot
Class IIIb cover
Punch planter opener
U-shaped holes
Class I cover
Surface broadcast
No slot Class I cover
R NR R NR R NR R NR R NR R NR
% seedling
emergence with
earthworms
17 25 65 40 76 48 63 62 17 15 84 87
Earthworm number
(per core)
9 8 22 13 25 13 23 14 18 10 22 14
% seedling
emergence without
earthworms
15 19 24 23 20 22 43 41 14 16 89 89
R, plots covered with surface residues, both before and after drilling; NR, plots with no surface residue covering, either before or after drilling.
Table 7.1. Effects of no-tillage openers on barley seedling emergence and earthworm numbers in a wet soil after drilling.
These results suggest that all three
observed trends are linked in a wet soil.
Indeed they are. The third line of Table 7.1
illustrates emergence when earthworms
were eliminated from the soil by poisoning
in an otherwise identical experiment.
Without earthworms, seedling emergence
was weakened with all drilling
treatments. Most residue advantages with
inverted-T- and U-shaped slots disappeared
in the absence of earthworms, indicating a
strong linkage between the three factors
when they were present. This also demonstrates
one of the longer-term benefits of
no-tillage, that of building up earthworm
numbers and organic matter, which work to
the advantage of this farming system, provided
that appropriate equipment is used to
maintain and capitalize on those benefits.
The data of Table 7.1 also illustrates
that mechanical aeration can to some extent
substitute for the absence of natural
aeration caused by earthworms and other
soil fauna. The chemical treatment to kill
earthworms also kills some of the other
channel-forming soil fauna. Although the
use of power till openers may only be of
short-term benefit when drilling into soils
that subsequently become wet, this was the
only opener to promote more than 24%
seedling emergence in the ‘sterilized’ soil.
Even then, the 43% emergence obtained
with this opener in residue and the 41%
without residue cannot be regarded as satisfactory
and do not compare with the 76%
obtained with the winged opener in the
presence of both earthworms and residues.
Surface broadcasting promoted the
highest seedling emergence counts in the
absence of earthworms (89% both with
and without residue), presumably because
seeds on the surface were unaffected by
earthworm activity beneath it. But this treatment
can hardly be considered a recommended
field practice unless one can
guarantee 400 mm of rainfall for the first
20 days after sowing. It was used in this
experiment solely to compare the seed’s
need for oxygen and water.
Figure 7.4 illustrates similar responses
to those just presented for inverted-Tshaped
slots, hoe (U-shaped slots) and vertical
double disc (V-shaped slots) openers. The
most noticeable effects are that the seedling
emergence trends follow the trends of earthworm
numbers with all openers and that
residues increased both emergence and
earthworm numbers with the inverted-T
and hoe openers but not with vertical
double disc openers.
To further understand the interactions
between opener types, the moisture status
92 C.J. Baker
Fig. 7.4. Responses of seedling emergence and earthworm numbers to three contrasting, no-tillage
slot shapes and surface residues in a wet soil (from Baker et al., 1996).
of the soil and the level of residues present,
Chaudhry (1985) conducted an experiment
in which these factors were varied independently.
The results are shown in Table 7.2.
The data show that most openers performed
reasonably well in favourable soil
moisture conditions, regardless of the level
of residue (range, 65–90% seedling emergence).
When the conditions became wet,
however, the shortcomings of the vertical
double disc opener (V-shaped slot) became
progressively more apparent as the length
of the residue increased. In the wet soil,
emergence from the V-shaped slot dropped
from 38% with no residue to 35% with
short residue and 30% with long residue.
The winged and hoe openers, in contrast,
performed best when long residue covered
the wet soil, which was attributable to the
increase in earthworm activity in response
to the long residue. As the residue length
was reduced with these two openers, their
advantages over the vertical double disc
opener were reduced or eliminated.
Although the hoe opener responded
positively to long residue, it is difficult to
actually make a hoe-type opener function in
long residue in the field. It is one thing to do
this on a plot scale for experiments but, in
the field, hoe openers soon block because of
their raking action. In practical terms, therefore,
of the two openers that performed well
in wet soils with long residue, only the
winged opener (inverted-T-shaped slot),
which is able to handle residues in its disc
form, can be regarded as a practical option.
Opener performance
The performance of various seeding openers
in soil (that is, wetted after seeding) can be
summarized as follows.
Power till openers (U-shaped slots)
These openers, in the absence of earthworms,
will provide some compensatory
mechanical aeration. The presence of earthworms,
however, will not necessarily result
in any improvement to seedling emergence
because the gains that mechanical aeration
brings to an earthworm-populated soil are
offset by physical burial of the food source
for any surface-feeding earthworms. There
will also be some actual destruction of
earthworms in the slot zone, but because
the width of tillage by such openers is normally
very narrow, it is likely that the slot
zone will be rapidly recolonized by earthworms
from the undisturbed soil alongside.
Punch planting (V- or U-shaped holes)
This is not likely to produce good results,
with or without earthworms, although
further work needs to be conducted with
such openers. The poor performance of the
punch planter in these experiments was
somewhat surprising since the method used
to make holes did not result in any compaction.
In practice, punch planters almost
invariably produce V-shaped holes, which
could be expected to behave in much the
Drilling into Wet Soils 93
Seedling emergence %
Vertical double disc opener
V-shaped slot Class I cover
Hoe opener U-shaped slot
Class I and IIIa cover
Winged opener
Inverted-T-shaped slot
Class IV cover
LR SR NR LR SR NR LR SR NR
Adequate
moisture
65 84 82 86 70 76 90 76 82
Wet soil 30 35 38 68 36 42 75 43 47
LR, long residue; SR, short residue; NR, no residue.
Table 7.2. Effects of openers, residue levels and soil moisture status on barley seedling emergence
from a soil containing earthworms.
same way as continuous V-shaped slots. In
this case, however, a small coring device
was used to remove cores of soil without
compaction.
Vertical double disc openers
(V-shaped slots)
These can be expected to perform poorly in
wet soils for two reasons. First, compaction
and smearing, together with crust formation,
result in earthworms avoiding the slot
area. Thus, not only does the opener disadvantage
the seeds directly, it discourages
natural processes (earthworms) from repairing
the damage.
To examine the tolerance of earthworms
to smearing, Chaudhry (1985) placed
a number of earthworms on the surface of
a damp, smooth soil contained in two
high-sided pots (to prevent escape of the
earthworms). Before placing the earthworms
on the soil, he lightly smeared the
surface of one of the plots with his finger.
Overnight, all of the earthworms on the
un-smeared soil had burrowed into the soil
while only half had achieved the same
result in the smeared soil, indicating the
difficulty earthworms have in burrowing
through smears.
Chaudhry (1985) also tested the tolerance
of earthworms to compaction and
found much the same result as for smears.
Because wet soils are softer than dry soils,
the action of vertical double disc openers
acting through surface residues on wet soils
is more one of pressing than cutting. This
accentuates their compaction tendency.
Slots that are both smeared and compacted
are largely avoided by earthworms and do
not benefit from their burrowing or nutrient
cycling (Baker et al., 1987, 1988).
Secondly, double disc openers tuck (or
hairpin) residues into the slot. In wet soils,
Lynch (1977, 1978) and Lynch et al. (1980)
showed that the decomposition of this residue
produces fatty acids, in particular acetic
acid, which tend to kill seeds and germinating
seedlings. They looked at ways of countering
this problem, ranging from applying
lime with the seed to neutralize the acid to
separating the seed from the residue.
Apparently, separation of the two by
only a small distance will largely avoid the
problem since acetic acid is very quickly
broken down in the soil by bacteria. The
residue tucking problem is reflected in
the negative response to the presence of
residue by the vertical double disc opener
and the fact that this negative response
increased as the length of residue (and size
of hairpins) increased.
Although slanted double disc and
angled disc openers were not included in the
above experiment, it is known that both of
these openers also tuck residue into the seed
zone, in much the same manner as vertical
double disc openers. They can therefore be
expected to experience acetic acid fermentation
and its detrimental effects on seeds, but
should experience fewer problems associated
with smearing or compaction.
Winged openers (inverted-T-shaped slots)
These return most of the residue to a position
over (not inside) the slot. This encourages
earthworms to colonize the slot zone
because when the residue is removed, the
earthworm numbers decline noticeably.
The central disc of the disc version of the
winged opener will hairpin residues, in
common with every other disc-type opener.
But the winged side blades of this opener
place the seed to one side of the central slit
and therefore remove the seed from contact
with the hairpinned residue. This is probably
the only disc-type opener that effectively
prevents seeds from lodging within
hairpins and for this reason benefits from
the presence of residues even in wet conditions.
When long residue was positioned
over the slot, the inverted-T slot produced
more seedling emergence than any other
design.
Hoe openers (U-shaped slots)
These behave in a similar manner to winged
openers except that instead of placing the
residue over the slot, they tend to push it to
either side. As a consequence, although hoe
openers will produce a positive response to
the presence of residue (in terms of seedling
94 C.J. Baker
emergence and earthworm numbers), that
response is not likely to be as strong or as
positive as for winged openers.
The seedling emergence responses of
the various openers and surface broadcasting
have also been reflected in root and
shoot weights of the seedlings, as shown in
Figs 7.5 and 7.6 (with and without earthworms,
respectively).
Without earthworms, there were few
differences between openers. Only the
mechanical aeration of power till openers
had any positive effect. With earthworms,
however, the seedling growth closely paralleled
the trends of seedling emergence and
earthworm numbers.
Figure 7.7 shows typical oxygen diffusion
rates within the soil containing earthworms
associated with winged and double
disc openers (Chaudhry, 1985; Baker et al.,
1987, 1988). Oxygen diffusion rate is measured
by passing a current through platinum
electrodes placed in a grid pattern
around the sown slots and measuring the
rate of consumption and replacement of
oxygen in the vicinity of the electrodes (see
Chapter 19).
Figure 7.7 shows that the winged
opener had no negative effect on the oxygen
status of the soil. The oxygen status surrounding
the hoe, power till and punch
planter openers (not shown) was very similar
to that of the winged opener. In fact, all
of these openers had similar patterns to that
of the undisturbed soil, indicating that none
of them had any detrimental effect on the
oxygen diffusion rate of the soil. But, in
all cases, the presence of residues moved
the high-oxygen zones closer to the seeds,
probably as a result of increased earthworm
activity.
In contrast, the double disc opener had
a marked negative effect on the oxygen
status of the soil, regardless of the presence or
absence of residues. Essentially, this opener,
because of its wedging action, squeezes the
high-oxygen zones away from the immediate
vicinity of the seeds altogether and replaces
them with compacted zones of low or, at best,
medium oxygen diffusion.
Also of note is that the effects of
wetness on the soil, both with and without
earthworms, seems not to be related to
how the soil becomes wet. For example,
Drilling into Wet Soils 95
Fig. 7.5. Root and shoot weights of
no-tilled barley seedlings in response
to opener types and residue in the
presence of earthworms (from Baker
et al., 1988).
Chaudry (1985) had earlier conducted two
experiments with earthworms and residue,
identical in all respects except that one
used simulated rainfall to wet the soil after
drilling and the other used a rising water
table. He was particularly interested in
whether or not persistent rainfall had some
sealing effect on the internal faces or the
cover, or, alternatively, washed the seed
out. He found no differences in barley
seedling performance between wetting the
soil from above or below, but both experiments
confirmed the differences between
openers and residue.
96 C.J. Baker
Fig. 7.6. Root and shoot weights of
no-tilled barley seedlings in response
to opener types and residue in the
absence of earthworms (from Baker
et al., 1988).
Fig. 7.7. Oxygen diffusion rate profiles around winged and double disc no-tillage openers operating
in a wet silt-loam soil, in the presence and absence of surface residues (from Baker et al.,1988).
Later, Giles (1994) quantified the rate
of accumulation of earthworm biomass in
the top 100 mm of soil as a function of different
levels of barley straw on the surface
of the ground in New Zealand. He found an
almost linear relationship, in which the
total biomass of two surface-feeding species
(L. rubellus Hoff and A. caliginosa Sav)
had accumulated to 9 t/ha under 11 t/ha of
straw and 5.1 t of earthworms under 6.4 t/ha
of straw. During that period the recoverable
biomass of the straw had decreased from
11 t/ha to 3.2 t/ha and 6.4 t/ha to 1.2 t/ha,
respectively. For the first 6 months, the
heavier rate of residue remained wetter than
the lighter rate, which might help account
for the faster decomposition of the former.
At the termination of the experiment, a part
of the residues appeared to have decomposed
while another part had simply been
buried by earthworm casts.
It should be appreciated that these
levels of cereal straw were deliberately set
very high to test the ability of earthworms
to cope with ‘overload’ conditions under
no-tillage. In general terms, such straw
levels equate with grain yields of about the
same magnitude.
Finally, experiments relating to wet
soils would not be complete without also
measuring the infiltration of water into the
slot zones in the field. Figure 7.8 shows the
results of a field experiment that compared
the infiltration rates of a range of openers in
a residue-covered silt-loam soil containing
earthworms (Baker et al., 1987). The results
Drilling into Wet Soils 97
Fig. 7.8. Infiltration rates of
no-tillage slots in a silt-loam soil
(from Baker et al., 1987).
reflect earthworm and seedling emergence
trends. The winged opener (inverted-Tshaped
slot) produced the most rapid infiltration
(110 mm/h after 2 h), which is not
surprising since it had promoted the
greatest earthworm activity and seedling
emergence. Next was a group of openers
including hoe, power till (U-shaped slots)
and punch planter (U-shaped holes),
together with the undisturbed soil, all of
which averaged 70 mm/h after 2 h. The
poorest infiltration was with the double
disc opener (V-shaped slots), with only
20 mm/h infiltration after 2 h. Water
remained puddled in the V-shaped slots
for hours after the experiment.
Summary of Drilling into Wet Soils
1. The ranking for the three basic slot
shapes from poorest to best (V, U and
inverted-T) in wet soils containing earthworms
and residues is exactly the same as for
dry soils, but for somewhat different reasons.
2. Seeds need ready access to oxygen in a
wet soil, and different openers create different
oxygen environments around the seeds
in wet soils.
3. Double disc openers have an adverse
effect on the oxygen diffusion rate of the
soil surrounding the seed slot.
4. Inverted-T, hoe and power till openers,
together with punch planters, have either a
neutral or positive effect on oxygen diffusion
around the slot.
5. Both earthworms and surface residues
give clear-cut advantages if managed correctly.
Both will increase with time under
no-tillage and have an increasingly positive
effect on aeration, drainage and infiltration.
6. Winged and hoe openers encourage
earthworm activity in the slot zone.
7. Surface residues encourage earthworm
activity, with the amount of activity being
proportional to the amount of residue.
8. The ability of the inverted-T-shaped
slot (winged opener) to retain residue over
the slot is as important in wet soils as it is in
dry soils because it encourages earthworm
activity within and around the sown slot.
9. Double, triple and angled disc openers,
together with punch planters, tend to tuck
(hairpin) residue into the seed zone, where
it has a negative effect on germination and
seedling vigour. This is especially true of
long, stringy and damp residue.
10. Winged, hoe, power till and furrow
openers effectively separate decaying residue
from direct contact with seeds.
11. In the absence of earthworms, mechanical
aeration of the slot by power till
openers may have a short-term benefit.
12. Surface broadcasting can perform well
if regular daily rainfall is available for
3 weeks after sowing, but obviously this
cannot be regarded as a practical option.
13. V-shaped slots and punch planter
holes tend to be compacted and/or smeared.
Class I cover (or lack of cover) allows these
smears to dry to form crusts.
14. Smears and/or crusts discourage earthworm
activity in the slot zone.
15. U-shaped slots created by hoe, power
till and furrow openers may be smeared but
only minimally compacted. If Class II cover
or better is possible, the smears should not
dry to become crusts.
16. U-shaped slots created by angled disc
openers will not be smeared or compacted.
17. Inverted-T-shaped slots created by
winged openers may be smeared but not
compacted. Class IV cover will prevent
drying of smears.
18. Excellent water infiltration is possible
with inverted-T-shaped slots but infiltration
is likely to be poor with V-shaped slots
created by double or triple disc openers.
But infiltration between the rows can be
expected to be greater with no-tillage than
with traditional tillage anyway, particularly
with increased earthworm populations and
organic matter.
19. Excellent seedling emergence can be
obtained by inverted-T-shaped slots in wet
soils, and satisfactory emergence can be
obtained by most of the openers that create
U-shaped slots.
20. Poor seedling emergence will result
from V-shaped slots or holes in wet soils.
98 C.J. Baker
8 Seed Depth, Placement and Metering
C. John Baker and Keith E. Saxton
Accurate seed placement is more important in
no-tillage than in tillage.
When an opener on a no-tillage drill or
planter deposits seed, and perhaps fertilizer,
into the soil, its ability to control the
final placement and environment of each
depends on a number of sometimes contradictory
functions. The required combined
capability of the drill or planter and soil
opener includes:
1. Continuously following the soil surface
of each row and maintaining precise seeding
depth.
2. Dispensing seed under the soil, on the
move, in a consistent band relative to the
opener itself.
3. Covering the seed (and perhaps fertilizer)
or at least making provision for effective
covering after the opener has passed.
4. Separating the seed from the fertilizer if
the two are being placed at the same time
and optimizing the positions of each relative
to one another so as to maximize biological
responses.
5. Metering and dispensing seed at the
desired spacing and in the desired pattern
along the row.
6. Transferring seed from the metering
mechanisms to the openers without disrupting
the intended spacing or pattern.
Functions 1–3 are important for proper
seed placement and function. Function 4 is
important for fertilizer placement, as described
in Chapter 9. Functions 5 and 6 (and,
to some extent, 1) are dependent on the design
of the whole drill or planter, especially
the drag-arm configuration and downforce
mechanism, as well as the openers.
Placing seed and fertilizer in the soil is
a function of opener design. For optimum
performance, openers need to have the
ability to:
● Ignore or control soil disturbance
beneath the ground surface (or lack of it
when soils are wet).
● Ignore soil stickiness.
● Cope with stones and other obstructions
beneath the surface.
● Avoid depositing seeds in hairpinned
residue.
● Prevent seed bounce.
● Cover the slot to a consistent depth.
Covering might be a separate operation
performed by a separate machine (e.g. harrows),
in which case the openers should
create the slots in such a way that the covering
operation will result in a consistent
depth of cover (see Chapter 5).
Seed metering is a function of the seed
metering mechanism of the drill or planter
© FAO and CAB International 2007. No-tillage Seeding in Conservation
Agriculture, 2nd edn. (eds C.J. Baker and K.E. Saxton) 99
and is not peculiar to no-tillage. In general,
a precision planter is distinguished from a
drill by the fact that a planter dispenses single
seeds with the intention that the seeds
are placed a predetermined distance apart.
A drill, on the other hand, dispenses seeds
in bulk so that a given number (or weight) of
seeds is deposited in a given length of row
(or area) in an approximately uniform distribution
with no attempt at individual seed
spacing.
Transferring seed from the metering
mechanism to the opener might seem a
mundane function, but, with precision
metering especially, this transfer must
maintain the continuity of metered seed
timing for accurate spacing in the row.
Agronomists argue about the effects of variations
in seed spacing on crop yield, especially
when this is traded off against the
natural variation between plants and their
abilities to compensate for imperfect spacing.
But most experts agree that there is little
agronomic disadvantage from having seeds
spaced at precise intervals along the row.
Recent evidence for maize suggests that uniform
seeding depth and emergence are likely
to be more important than plant spacing.
Seeding Depth and Seedling
Emergence
Almost everyone agrees that seeding depth
should be as consistent as possible. But surprisingly
there have been few studies quantifying
the target depths for seeds sown under
no-tillage (as distinct from tillage) or the
crop performance effects of variations around
that target depth. Obviously, the importance
of this factor will vary with the compensatory
growth potential of any given crop or
species.
To quantify the effects on seedling
emergence of imperfect drilling depth under
no-tillage, Hadfield (1993) measured the
variations in germination and emergence of
wheat (Triticum aestivum) and lupin (Lupinus
angustifolius) drilled in inverted-T-shaped
no-tillage slots at various depths. The results
are shown in Table 8.1.
Hadfield concluded that the particular
variety of wheat he used (cv. Otane) was
less sensitive to depth of sowing than lupin
in the 20 mm to 50 mm depth range, but
both were seriously affected by depths greater
than 50 mm. Overall, seedling emergence
with this variety of wheat decreased by 4%
for each 10 mm increase in drilling depth
between 20 mm and 70 mm. But other varieties
of wheat have been observed to have
quite different tolerances of depth. In comparison,
in these experiments lupin emergence
declined by 17% for each 10 mm
increase in depth between 20 mm and
70 mm. In both cases, the reduction in seedling
emergence was not caused by failure of
seeds to germinate but by subsurface mortality
of seedlings that had already germinated.
This confirmed earlier observations
by Heywood (1977).
Campbell (1981, 1985) also studied
drilling depths of a small-seeded pasture
legume, red clover (Trifolium pratense),
sown in inverted T-shaped no-tillage slots.
He concluded that seedling emergence of
100 C.J. Baker and K.E. Saxton
Seedling emergence* (plants per square metre in parenthesis)
Nominal drilling depth Wheat Lupin
20 mm 79% (209) a 93% (66) a
30 mm 80% (210) a 87% (62) b
50 mm 73% (192) a 60% (43) c
70 mm 61% (160) b 24% (17) d
Unlike letters in a column denote significant differences, P < 0.05.
*% seedling emergence = % of the estimated number of seeds sown from the known weights
of seeds sown.
Table 8.1. Effects of drilling depth on seedling emergence of no-tilled wheat and lupin.
pasture legumes was particularly sensitive
to drilling depths above and below his midtreatment,
13 mm. The results are shown in
Table 8.2.
Salmon (2005) examined the effects of
seeding depths (from 0 to 50 mm) on the
emergence of brassica seedlings when sown
into a range of no-tillage soils in New Zealand
using the disc version of winged no-tillage
openers. He also sought interactions with
seed treatments, which ranged from coated
(Superstrike), insecticide-treated (Gaucho®),
to bare (untreated) seed.
He concluded that, with this particular
opener, which is known to create a favourable
environment for both seeds and seedlings,
depths of sowing from 10 to 25 mm
had no significant effect on the rates or final
counts of seedling emergence, but that zero
depth and 50 mm depth reduced emergence
markedly. There were no interactions between
seeding depths and seed treatment.
Salmon was not able to test the effects
of low seed vigour, other brassica species
and/or other no-tillage opener types in these
experiments. It is doubtful, however, if any
of these factors would have improved the
range of sowing depths found possible,
which was considered to already be unusually
broad in Salmon’s experiments.
Maintaining Consistent
Opener Depth
Maintaining a consistent depth of seeding is
one of the most demanding tasks that any
no-tillage machine must perform. This is for
several reasons:
● The surfaces of untilled soils do not get
smoothed in the same way that tilled
soils do.
● Untilled soils are often harder than tilled
soils and therefore have less cushioning
effect, causing more bounce of the openers,
especially at higher speeds.
● The harder soils require greater downforces
to push the openers into the
ground. Variations in ground resistance
therefore result in larger variations in
seeding depth than where soils are
softer and smaller downforces are used.
● The hardness or strength of untilled soils
usually varies across a field as a result of
natural settling of the soils. Regular
pulverization by tillage virtually eliminates
these differences in soil strength.
● No-tilled soils are often covered with
surface residues, which might interfere
with the opener’s ability to manipulate
the soil beneath it and further accentuate
the surface roughness.
We shall consider each of the above aspects
separately.
Surface following
Control of opener depth is partly a function
of the opener and partly a function of the
supporting drill or planter frame. With
no-tillage, there is little or no opportunity to
smooth the soil surface prior to drilling.
No-tillage openers must therefore have
superior surface-following ability compared
with their counterparts for tilled soils. The
extent of vertical mechanical movement
alone should increase from approximately
± 75 mm (total 150 mm) travel for tilled
soils up to ± 250 mm (total 500 mm) travel
for untilled soils.
Depth-gauging devices
One of the important contributions that
openers make to controlling seeding depth
is the presence or absence of depth-gauging
Seed Depth, Placement and Metering 101
Nominal
drilling depth
Seedling
emergence* (%)
0 mm 53% b
13 mm 89% a
38 mm 56% b
Unlike letters in the column denote significant
differences, P < 0.05.
*% seedling emergence = % of the estimated
number of seeds sown from the known weights
of seeds sown.
Table 8.2. Effects of drilling depth on seedling
emergence of no-tilled red clover.
devices (wheels, skids or bands), which
‘track’ the soil surface. Penetration forces
are generally higher for untilled soils than
for tilled soils. Further, the soil strength of
tilled soils is usually quite uniform across
the entire field as a result of the tillage process,
while soil strengths of untilled soils
vary quite widely on a metre-by-metre basis.
The result is that, if an opener relies
solely on the penetration downforce reaching
equilibrium with the soil’s resistance to
penetration in order to maintain a consistent
seeding depth, as is common in tilled
soils, seeding depths in untilled soil will
vary just as widely as the soil strength. Consequently,
any opener designed to operate
at a consistent depth in an untilled soil will
need at least some form of depth-gauging
device. With such an attachment, a downforce
can be applied in excess of that
required to just attain target depth for that
particular metre of soil. The additional force
is carried by the gauging device without
materially altering the depth of seeding.
Clearly, depth-gauging devices for
untilled soils need to have the capacity to
absorb quite large variations in applied force
to operate satisfactorily in the inherent
variability of such soils. Fortunately, untilled
soils also have an inherently high ability
to withstand surface loading and avoid
furrowing.
There are differences in the accuracy of
depth-gauging devices according to how
close to the point of seed release the gauging
device is located. Obviously, being closer to
this position results in more effective depth
control. The effectiveness of the device may
suffer if it is located too far from the seed
deposition zone since, for example, it may
register on a small hump when the seed is
being released into a small hollow.
There are often mechanical limitations
to where the gauging device can be located
on an opener in relation to where the seed is
finally ejected into the soil. Probably the
nearest any opener designs have come to
gauging depth precisely at the seed exit
points are those on which a specially shaped
semi-pneumatic tyre operates alongside
(touching) the base of a disc at the point
where the seed is ejected. Figure 8.1 shows
such an arrangement.
Where possible, it is desirable to combine
the depth-gauging function of wheels
with the additional function of slot covering
and/or closure, so long as one function
is not markedly compromised by the
102 C.J. Baker and K.E. Saxton
Fig. 8.1. Depth-gauging wheels located alongside the point of deposit of seed in a no-tillage opener.
requirements of the other. The depth-gauging
wheels on the disc version of winged openers
are located close to, but slightly rearward
of, the seed-ejection zone so that they can
perform these dual functions without significant
compromise to either (see Fig. 4.27).
The wheels in Fig. 8.1 do not perform a slotclosure
function.
Almost universally, the gauging devices
most favoured by opener designers are
wheels, although skids and depth bands are
also used on less expensive opener designs.
The problems with skids in no-tillage are
that they gather and block with residue and
the higher down forces result in high wear
rates as they slide along the ground.
Depth bands are sometimes attached to
the sides of discs to limit the depths of their
penetration, but the depth of seeding cannot
be conveniently adjusted for different crops
without removing the band and replacing it
with a band of different diameter. They also
tend to accumulate soil in the corner between
the band and the disc, effectively increasing
the diameter of the band and decreasing the
seeding depth.
Gauge wheels are not without their
problems either. Because wheels can only
be attached by their axles, designers have to
trade off the disadvantages of attaching them
behind the opener against the disadvantages
of attaching them beside the opener, where
they might interfere with residue clearance
and are unlikely to be able to function in a
slot-closure capacity as well.
Since most no-tillage openers for residue
conditions involve a disc of some nature as
the central component, the disadvantage of
locating gauge wheels behind the opener
can also take on a new and additional dimension
because the distance from the seed
zone then increases by at least the radius of
the disc. Consequently, despite their advantages
for controlling depth of seeding, many
no-tillage opener designs do not use gauge
wheels at all. With those that do, most are
located either beside the opener or partly
beside and partly behind it.
A further complication arises when
gauge wheels are required to perform the
additional function of covering the slot.
Wheels that only function for covering are
called ‘press wheels’, those that only gauge
depth are ‘gauge wheels’ and those that perform
both functions are ‘gauge/press wheels’.
Few openers have gauge/press wheels.
One reason is that, for accurate depth control,
the wheel should operate alongside the
seed deposit zone, while for effective pressing
the wheel should follow behind the
opener. Furthermore, the wheel must roll on
undisturbed soil to maintain depth control,
while for useful slot pressing the wheel
should be on either the loose soil over the
slot or in the slot itself (see Chapter 5). These
somewhat contradictory requirements often
lead either to two separate wheels or to one
of the functions being compromised in the
interests of cost and residue clearance. In
general, if the wheels on openers are supported
by springs, they will probably be
there solely for the press wheel function
rather than also as gauge wheels.
The wheel on the opener shown in
Fig. 8.1 is solely a gauge wheel. A smaller
separate press wheel can be seen operating
at an angle behind the disc.
An example of combined press/gauge
wheels is shown in Fig. 4.27, where two
wheels are used on either side of a central
disc and slightly rearwards of the seed zone.
The wheels are sufficiently wide to register
on the undisturbed soil alongside the opener
(the gauge wheel function) but are also
angled so that they fold the flaps of residue
and soil back over the inverted-T-shaped slot
and gently press on it (the press wheel function).
Inverted-T-shaped slots do not require
pressing on the seed in the slot, so there is
no disadvantage from only pressing on the
top of the covered slot (see Chapter 6). The
depth-control function of this opener is
slightly compromised because the wheels
are not located exactly at the seed release
point, but there are other systems employed
with this opener (see below) that more than
compensate for this shortcoming.
The value of semi-pneumatic tyres
It is appropriate here to pay tribute to
semi-pneumatic tyres, which are used on
most modern press wheels and gauge wheels.
Seed Depth, Placement and Metering 103
This often undervalued invention is one of
the most successful adjuncts to agricultural
machinery. Until semi-pneumatic tyres were
invented, all gauge/press wheels were either
rigid wheels or, at best, solid rubber, plastic
or fully inflated tyres.
Because press wheels on seed drills
almost invariably operate at least partially
in a disturbed soil zone, even in no-tillage,
they are very inclined to accumulate mud
in damp conditions. Flexure is the most
effective means for a wheel to shed accumulated
mud. Fully inflated tyres under normal
pressures and rigid wheels do not flex
sufficiently to shed mud. Some no-tillage
situations may require enough downforce
for a limited flexing by fully inflated tyres.
A method had to be found to combine
flexure with maintaining the accuracy of
the gauging radius of the wheel, i.e. it had to
be able to flex but still retain a predictable
loaded radius, regardless of the loading on
it. This is where semi-pneumatic tyres excel.
Although they are hollow (in a multitude of
cross-sectional shapes), there is no air pressure
within them. Indeed, most have a small
bleed hole so that air cannot be permanently
trapped inside. The distance between the
outer wall and the inner wall (against the
rim) is relatively small. In operation, where
the footprint zone contacts the ground, the
outer wall collapses temporarily and presses
against the inner wall and thence the rim.
As it leaves the ground, the resilience of the
rubber causes the outer wall to return to its
original position. In so doing, the outer wall
continually flexes in and out, which dislodges
mud. The operating radius remains
predictable so long as there is sufficient
force applied to collapse the outer wall
against the inner wall and rim in the footprint
zone.
Walking beams
Another adjunct to no-tillage openers is the
use of ‘walking beams’ for mounting the
gauge wheels, such that a pair of wheels
can independently move vertically while
continuing to share the down pressure.
These are simple mechanical leverage
systems, which are applicable where there
are at least two gauge wheels. A single linkage,
pivoted at its centre, joins the mounting
brackets for the two wheels in a pivotal
manner. The two wheels find their own
positions by equalizing the footprint forces
about the pivoting walking beam. The equalized
positions of the two gauge wheels
constantly change as each wheel in turn
encounters changes in the soil surface. As
one wheel moves upwards, the other wheel
moves downwards.
The point of this arrangement is that as
each wheel encounters a small rise or hollow
the whole opener is forced to rise or fall by
only half the height of the rise or depth
of the hollow. Thus surface roughness is
smoothed by a factor of a half, which is
important for no-tillage in the absence of
general smoothing by tillage.
Figure 8.2 shows a walking beam
arrangement for a pair of gauge wheels.
104 C.J. Baker and K.E. Saxton
Fig. 8.2. A walking beam arrangement for
equalizing the loads carried by two independent
gauge wheels.
Disc seed flick
The tendency of double disc openers to
flick seeds out of the ground arises when
seeds become clamped between the two
discs at or near the pinch point where they
touch. At speed, as the discs move apart
again behind this point, the clamping
action, followed by sudden release of the
seeds, may propel them upwards and rearwards,
expelling them from the slot.
The problem is overcome by dropping
the seeds behind the pinch-point zone and/
or by inserting covering plates in the zone
between the two discs at their rearmost
edges.
With all disc openers in sticky soils, at
least one surface of the disc can become
sticky. Seeds may either adhere to the disc
and be lifted from the slot or soil may stick
to the disc and carry seeds out with it.
With double disc openers, the seed is
released against the inside surfaces of the
discs that are not in contact with the soil.
Thus, seeds seldom stick to the discs but
soil sticking to the outside of the discs can
seriously disrupt the integrity of slot formation
and carry seeds, which have already
been deposited, out of the slot (see Fig. 8.3).
With angled discs, the seed side of the
disc is largely sheltered from soil contact,
which helps to avoid seeds sticking directly
to the disc.
The disc version of the winged opener
has special subsurface scrapers designed to
wipe sticking seeds off the disc below the
ground (Thompson, 1993; Fig. 4.27).
Soil disturbance
With most disc openers, even when operating
in non-sticky soils, a certain amount of
soil disturbance occurs as the disc leaves
the bottom of its rotation. This also occurs
with hoe openers as the rigid shank moves
forward in the soil. While seeds might not
be flicked out of the soil by this soil movement,
it may redistribute the seeds so that
they occupy more random vertical positions
within the soil than would otherwise be
expected.
With some power till openers, the soil
is deliberately disturbed and the seed is
deposited into the rotor area while slot tilth
is being formed, with the intention of thoroughly
mixing the seed and soil. While this
undoubtedly achieves its aim, the resulting
variation in the depths of individual seeds
does little for consistency of germination,
emergence and maturity.
Residue hairpinning or tucking
The tendency of discs in any configuration
to hairpin, or tuck, residue into the slot
without actually cutting the residue often
leaves the seeds embedded in or on this
residue rather than in contact with clean
soil. Many poor no-tillage plant stands have
resulted from the hostile seed environment
created by residue tucked directly into the
seed slot. This occurs with both dry and wet
residues, although the cause of the problem
is different in the two cases.
With tough resilient residue, such as wet
maize stover, the residue may quickly
straighten out again after passage of the disc,
in which case it may flick a portion of the
seeds out of the slot. Figure 8.3 shows a soybean
(Glycine max) seed that has been flicked
completely out of a slot by a maize stalk after
passage of a vertical double disc opener.
But, even if seeds are not flicked out,
when they become embedded in dry hairpinned
residue, they will not have effective
seed–soil contact, this affects imbibition
and germination. In wet soils, the fatty
acids that are the products of decay of the
residues cause seed and seedling mortality
(see Chapters 6 and 7).
Opener bounce
Hoe-type and simple winged openers,
which are under considerable downforce
for penetration, often bounce in response to
variations in soil strength, particularly at
high speeds, disrupting the accuracy of seed
ejection into the soil.
But disc-type openers are not immune
either. Any opener is capable of leaving
Seed Depth, Placement and Metering 105
seeds on the surface after encountering
stones in the soil. Hoe-type openers tend to
push stones aside or flick them out of the
ground, whereas disc-type openers tend to
rise up and over stones and deposit seeds
on top of the ground.
Seed bounce
As a result of high operating speeds and
seeding into dry cloddy soils, large seeds
often bounce upon contacting the soil. In
severe cases, some seeds bounce right out of
the slot.
The problem is accentuated with some
air delivery systems when excessive delivery
velocity of the air and seeds is used,
which, combined with a high forward speed
of the opener, may cause severe seedbouncing
problems.
Slot closure
Problems such as seed bounce can be
largely overcome if the opener self-closes
the slot immediately after it has been
opened to receive the seed. Some winged
openers, slanted double disc openers and
power till openers are examples of openers
with good self-closing abilities.
Drill and Planter Functions
Downforce mechanisms
The most common downforce mechanisms
for conventional drills and planters are
springs. But springs change their loading
forces in a linear fashion with changing
length (i.e. they change their forces by the
same proportion as their lengths change).
This might be acceptable for tilled seedbeds
because: (i) the loads applied are relatively
small and the springs are not significantly
compressed; (ii) the variations in ground
surface and therefore spring lengths are relatively
small; and (iii) springs are relatively
cheap and trouble-free.
For no-tillage seedbeds, however, the
opposite is true: (i) spring loads are high;
(ii) surface changes can be quite large; and
(iii) no-tillage drills are generally more robust
and expensive. Because spring loads are high,
106 C.J. Baker and K.E. Saxton
Fig. 8.3. A soybean seed (lower centre) that has been flicked completely out of a no-tillage slot made
by a double disc opener (from Baker, 1981a, b).
no-tillage drills tend to use either very heavy
and unresponsive springs or smaller-section,
longer springs compressed to short lengths.
Because the changes in spring force are
related to a spring’s compressed length at the
time, having a spring compressed to a short
length to achieve opener penetration magnifies
the force changes relative to length
changes. Accordingly, some no-tillage drills
and planters are designed with inordinately
long springs (Fig. 8.4), or, alternatively, the
springs are positioned near to the pivot
points of the drag arms so that dimensional
changes are minimized.
The force relationship with the length
of springs applies equally well if the springs
are arranged to be working in tension or in
compression. Compression is more common,
as it is difficult to overload a spring in compression
compared with a spring in tension.
For reasons of compactness, a few no-tillage
drills and planters use springs acting in
tension.
Either way, it is virtually impossible to
maintain constant downforces with springs.
A number of innovative designs have been
used with the objective of reducing the
shortcomings of springs. Some of these are
illustrated in Figs 8.5 and 8.6. In Fig. 8.5,
the mechanical springs have been replaced
with rubber buffers acting very close to the
pivot (fulcrum) of the drag arms to reduce
the required travel of the springs for any
one change in position. Rubber acts in an
almost identical manner to spring steel
with regard to the force it exerts in relation
to changes to its compressed length.
But problems from prolonged exposure
of rubber to ultraviolet light and retention
of ‘memory’ after long periods of compression
have made this an unpopular
choice.
In Fig. 8.6, the designers have attempted
to better equalize the spring forces across
the drill, to accommodate, for example, passing
over a hump on one side of the drill, by
dividing the bar that compresses the springs
into shorter articulating lengths. The effect
is similar to walking beams described above
for press wheels.
Another way to overcome the disadvantages
of springs for downforce application
is to provide the gauge wheels with
very large footprints and then apply excessive
downforces to ensure that the spring
force is sufficiently large to allow for lengthening
of the springs for the deepest hollow
likely to be encountered by the openers.
Seed Depth, Placement and Metering 107
Fig. 8.4. Long compression springs on a no-tillage drill.
Figure 4.24 illustrates a design that
has gone to the other extreme. In this case,
the total vertical opener travel has been
restricted by the use of spring tines that
move largely horizontally (backwards) in
response to increases in loading. The ground
surface-following ability of such drills is
poor, restricting their use to relatively
smooth fields and/or seeds that are very
depth-tolerant.
Regardless of the measures outlined
above, springs are generally an unsatisfactory,
108 C.J. Baker and K.E. Saxton
Fig. 8.5. No-tillage openers pressed into the soil with rubber buffers acting close to the fulcrum of the
drag arms.
Fig. 8.6. A no-tillage drill with an ‘equalizing’ spring arrangement.
though still the most common, way of
applying downforces to no-tillage openers.
Characteristically, their shortcomings can
regularly be seen in the field as too shallow
drilling through hollows and too deep drilling
over humps, leading to poor seedling
emergence in both situations. Figure 8.7
shows the travel of a no-tillage opener
with superior surface-following ability.
Unfortunately, not all no-tillage drills are
capable of achieving this degree of surface
following.
Compressed air
Fortunately, there are alternatives to springs.
The two most useful to date have been the
use of air and oil (hydraulic) pressure, acting
through rams or cylinders (Morrison,
1988a, b). The air pressure option uses large
volumes of air acting on large-diameter
cylinders attached to the drag arms.
Because it is difficult to compress air to
sufficiently high pressures to allow smalldiameter
cylinders to be used, there are
limits to the amount of downforce obtainable
with compressed air.
On the other hand, air is free and large
volumes can be compressed, with the result
that changes in volume resulting from
movement of openers up and down can be
designed to have a minimal effect on the
magnitude of the downforces. It should be
appreciated that any gas under pressure
has the same characteristics as mechanical
springs. At any given temperature, a change
in volume of the compressed gas will be
linearly proportional to its pressure. With
air, however, the volume can be made so
large that pressure changes with movement
of the openers can be minimized.
The biggest disadvantages of using air
directly are the limited amount of pressure
that can be practically obtained and the fact
that the oxygen in air under high pressure
can be explosive and that high-pressure air
cylinders need to be independently lubricated,
which is a problem in a semi-static
system such as this. Lubrication is easiest
where a continuous flow of compressed air
Seed Depth, Placement and Metering 109
Fig. 8.7. An example of excellent surface following through a hollow by no-tillage openers (gas-over-oil
downforce).
is used, such as with air tools. But in this
case the compressed air is contained within
a closed system, so lubrication is difficult.
Gas-over-oil systems
A more workable option has been to use oil
in a hydraulic system in equilibrium with a
compressed inert (non-explosive) gas (usually
nitrogen) contained in one or more
accumulators. This is referred to as a ‘gasover-
oil’, ‘oil-over-gas’ or ‘nitrogen-cushioned
hydraulic’ system. The volume of gas in the
accumulator(s), when the system is at its
likely operating pressure(s), needs to be
sufficiently large to reduce changes in pressure,
arising from changes in opener position,
to a minimum.
In reality, if the hydraulic cylinders on
all openers are connected in common (parallel)
to the hydraulic system, when one
opener rises in response to a rise on the soil
surface, another opener is likely to be falling
in response to a hollow somewhere else
across the drill or planter. Thus these two
openers simply exchange oil between them
without affecting the overall volume of
oil or pressure of the system to any great
extent.
Because of this, the need for large volumetric
changes by the hydraulic system as a
whole is much reduced. In contrast, mechanical
springs can only work with individual
openers unless a very complicated linkage
is used to obtain some measure of combined
action, as illustrated in Fig. 8.6.
Another advantage of the gas-over-oil
system is that, if the individual hydraulic
cylinders are of the double-acting type (i.e.
they can be powered in both directions),
these downforce cylinders can also be used
to lift the openers for transport. This eliminates
the need for a separate lifting assembly
on the drill or planter.
The biggest advantage of either gasover-
oil or air cylinders is that they can be
arranged so that the downforce on the openers
remains virtually unchanged throughout
the entire length of opener travel upwards
and downwards because the force exerted
by the cylinders remains constant throughout
their entire stroke length. This in turn
allows much greater vertical travel to be
designed into the openers for surface following
and depth control.
Figure 8.8 shows a no-tillage drill with
a gas-over-oil downforce system sowing at
the same depth on the top of an irrigation
110 C.J. Baker and K.E. Saxton
Fig. 8.8. An illustration of the extraordinary surface-following ability of a gas-over-oil opener
downforce system on a no-tillage drill.
border dyke as on the flat surface alongside,
and even part-way up the slope. Tillage drills
are never required to provide this much
opener travel and many simple no-tillage
drills do not achieve it either.
Automatic down force control (ADF)
A further refinement to the gas-over-oil system
is to equip the drill or planter with a
sensing device that measures the hardness of
the soil as the opener travels through it. This
signal is relayed to the hydraulic valving so
that, as the soil hardness changes (which
would otherwise alter the penetration depth
of the opener), the oil pressure is automatically
adjusted on the move to ensure that the
openers get the correct amount of downforce
to correctly maintain seeding depth in
each metre of the field. This sophistication
provides a fully automatic seeding depthcontrol
capability, unparalleled with current
technology.
Weights
One school of thought suggests that attaching
weights to individual openers would be
an effective way to ensure that each opener
experiences the same downforce throughout
its entire range of movement. But adding
and removing individual weights for a multitude
of openers on any one drill is impractical
and would require the operator to carry
surplus weights around in order to change
the downforces for new conditions. It would
also make changing the downforce on the
move within a field impractical, but, then
again, only the most sophisticated gas-overoil
systems with ADF allow this to be done.
Another downside to the use of weights
is that, when an opener rises or falls, the
inertia of the weight alters the effective
downforce and that this inertia is highly
dependent on the forward speed of the
machine, which determines the speed of
the rise and fall. For the technically minded,
inertia is proportional to the square of speed
in the direction of movement.
Where weights have their greatest use
is for single-row drills, since many of the
disadvantages above apply less to a single
opener than to multiple openers on a larger
drill and weights are often the cheapest
and most effective option available where
limited budgets apply (see Chapter 14).
Drag-arm design
The design and configuration of the drag
arms that attach the seed opener to the drill
frame are an important feature of drills or
planters that have an impact on seed placement.
A drill that has drag arms pivotally
attached to the drill or planter frame will
be designed to move the openers upwards
and downwards to accommodate changes
in the ground surface. This motion is provided
either by a hinged attachment to the
drill frame or by flexure of the drag arms
themselves.
In the case of flexed drag arms, the whole
drag arm must be constructed of spring steel.
There are advantages in that this eliminates
wearing joints, which, under the high forces
involved in no-tillage, can become a maintenance
problem. Such a desirable arrangement,
however, must be balanced against the
disadvantages of using mechanical springs
as the downforce system in the first place
and the difficulty in preventing the openers
from also flexing sideways, which interferes
with accurate row spacing.
With fully articulated (hinged) drag
arms, the most common arrangement with
conventional drills is to use a single arm
pivoting on a simple unlubricated joint, as
shown in Fig. 8.9. Because large forces are
required to push openers into and drag them
through the soil, there are quite large forces
acting on the pivot, especially if the source
of downforce is located close to the pivot
itself. As a result, the wear rate within the
pivoting mechanisms can be substantial.
This is an important issue with many
seemingly advanced no-tillage machines.
As new machines, they might appear to be
of sound design. But as the pivoting joints
wear, such machines soon provide poor
seeding accuracy and become unserviceable,
which creates an unforeseen cost penalty
against no-tillage.
More sophisticated no-tillage drill
designs provide pivots with lubricated and
Seed Depth, Placement and Metering 111
sealed bearings or heavy-duty bushings.
While this adds to the initial cost, it can
extend their service life to near that of the
tractors that pull them.
Parallel linkages
To ensure correct functioning, some no-tillage
openers must be maintained at a set angle
to the horizontal in the direction of travel.
Winged openers are a case in point. Such
openers often employ two drag arms (upper
and lower) arranged as a parallelogram in
such a way that the horizontal angle of the
opener remains unchanged throughout the
entire range of its vertical travel.
The disadvantages of such an arrangement
are the cost of the arms and pivots and
the fact that four pivots have greater potential
to create diagonal instability of the openers
than one or two pivots if they become worn.
To compensate, parallelogram drag arms are
usually wider and more robust than single
drag arms and utilize better-quality bushings
or bearings in the pivots. Undoubtedly,
they go another step towards perfecting
precision seed placement in no-tillage, but
to date they have only been included on
advanced planter and drill designs.
Figure 8.10 shows a no-tillage opener
mounted on parallelogram drag arms and
the extraordinary range of travel provided
by its gas-over-oil downforce system. The
hydraulic cylinder is difficult to see but can
be located from the position of the supply
hoses (top right).
A variation on parallelogram drag arms
is one where the parallelogram is designed
to be deliberately imperfect (i.e. a trapezium).
It is designed for operation with
winged openers that are pushed into the
ground with mechanical springs (Fig. 8.11).
The objective has been to reverse the geometrical
changes that occur with singlepivot
drag arms, in which the angle of the
wings normally becomes less in hollows
and increases over humps. The effect is usually
to accentuate the change in mechanical
spring forces by drawing the wings into the
ground more on humps than in hollows.
But, in this design, the wing angle increases
when the openers are in hollows and
decreases when they go over humps. Since
the steeper wing angle assists the opener to
pull itself into the ground, the arrangement
112 C.J. Baker and K.E. Saxton
Fig. 8.9. A simple single-pivot
drag-arm arrangement (slightly
modified from Baumer et al.,
1994).
Fig. 8.10. A winged no-tillage opener mounted
on parallelogram drag arms and pushed down with
a gas-over-oil system, showing its extraordinarily
large range of vertical travel, which is important in
no-tillage.
goes some way towards countering the
disadvantages of variable downforces with
mechanical springs.
Comparisons
The authors compared the capabilities of
two different no-tillage drills (both of which
featured gas-over-oil downforce systems)
in terms of their abilities to ignore surface
irregularities (Baker and Saxton, 1988).
Three types of tillage tool were used to cause
surface roughness in an otherwise smooth
untilled soil that had been chemically
fallowed. The roughness treatments were:
(i) chiselled with a shank chisel at 380 mm
centres operating 200 mm deep, which left
the roughest finish; (ii) cultivated with
250 mm wide sweeps operating 100 mm
deep (the next roughest finish); (iii) disced
once with a heavy double disc (the next
roughest finish); and (iv) no tillage at all,
which left a smooth surface finish. The
drills used are labelled in the diagrams as
‘Cross Slot’ (disc version of winged openers
that created inverted-T-shaped slots) and
‘Double Disc’ (vertical double disc openers
that created V-shaped slots).
The plant stands from the two drills
and four surface roughnesses are shown in
Fig. 8.12, and the resulting yields of winter
wheat are shown in Fig. 8.13. The ‘Cross
Slot’ drill had higher plant counts and
yields than the ‘Double Disc’ drill for all
surfaces, but significantly more so for the
rougher surfaces. The much heavier ‘Double
Disc’ drill had difficulty maintaining
depth control in the more loosely tilled,
rougher surfaces. The no-tillage surface was
easily penetrated by both drills, but the
double disc openers ‘tucked’ considerable
residue into the seed slot, which probably
contributed to the lower stands with that
drill in the very dry seeding conditions that
were experienced (see Chapters 6 and 10).
Seed metering and delivery
With small seeds sown on a mass basis, such
as grasses, legumes, brassicas and smallgrained
cereals, the seed metering devices
on drills are designed to distribute a continuous
trickle of seeds with no attempt to
single, or handle individual seeds separately.
Seed Depth, Placement and Metering 113
Fig. 8.11. A no-tillage opener in which a deliberately imperfect ‘parallel’ (trapezium) linkage is utilized.
As a result, such a trickle of seeds is largely
unaffected by the length or shape of the delivery
tubes that transport them from the seeder
to the opener, so long as there is sufficient
slope on the tubes for gravity to keep the
trickle moving consistently or a stream of air
to blow them along. Gravity delivery can be a
problem when drilling up and down hillsides,
where the drop tubes become too flat
to maintain the seed flow. With air seeders,
which substitute air flow for gravity, the air
flow transports the seeds in a consistent
manner to the openers and gravity plays
only a minor role.
Seed metering and delivery are generally
similar for no-tillage drills and drills
used in tilled soils, with only minor differences.
The seed metering mechanisms and
delivery tubes can be expected to be common
to both; however, the openers of
no-tillage drills are often spaced further
apart to clear residues and their vertical
travel may be greater than for tilled soils.
As a result, the seed delivery tubes may be
longer and have further to span from the
metering boxes to the openers, which may
cause them to lie at flatter angles. Compensation
for this loss of fall may involve raising
the seed boxes higher on the drill or the
use of multiple sets of seed boxes. Air
delivery becomes an attractive option,
since gravitational fall is then assisted by
the air flow (see Chapter 13). An example
of an advanced no-tillage drill with airassisted
seed and fertilizer delivery is
shown in Fig. 8.14.
114 C.J. Baker and K.E. Saxton
Fig. 8.12. The effects of surface
roughness on wheat seedling
emergence using two contrasting
drills (from Baker and Saxton,
1988).
Fig. 8.13. The effects of surface
roughness on yields of wheat
using two contrasting drills (from
Baker and Saxton, 1988).
Precision seeders that select single seeds
at regular intervals, such as maize, cotton,
beet and vegetable planters, provide a different
situation. Ritchie (1982) and Carter
(1986) showed that, once a single seed is
released from the metering mechanism into
a tube, its pathway through that tube may be
somewhat random. It will have a tendency to
bounce from wall to wall and at each bounce
it will lose an unpredictable portion of its
drop velocity. Consequently, any two seeds
seldom arrive at their destinations at exactly
the same time intervals from when they were
released from the metering mechanism.
Thus, even if a precision metering
mechanism selects individual seeds at precise
intervals, the precision of the intervals
at which consecutive seeds reach the ground
will depend on the pathways each follows
after leaving the metering mechanism. It is
even possible for a seed that took a more
direct route down a delivery tube to catch
up with and pass an earlier seed that bounced
on its way down the same tube.
For this reason, precision seed metering
mechanisms in tilled soils are located as
close to the soil as possible so that the seeds
have only a short drop, often without touching
the sides of any tubes at all. Commonly,
the distance of drop is about 50 mm and
often less. This free-drop approach is possible
only because tilled soils are prepared so
as to have no surface residues and are as
smooth and fine as possible, allowing the
bulky seeding mechanism to pass close to
the ground surface without the risk of
blockage or damage.
In no-tillage, however, surface residues
often protrude 300–500 mmabove the ground,
are variable in their nature and extent and
are often quite woody. Vertical clearance is
therefore necessary to avoid blockage. Further,
there is little or no opportunity to
smooth the surface of the soil. Consequently,
no-tillage openers are larger and more robust
than their tillage counterparts and the metering
mechanisms have to operate higher
above the ground. This necessitates seeds
having to be delivered up to 600 mm from
the metering mechanisms.
Free drop of seed is not an option
over such a distance in no-tillage because of
the effects of wind, slope and machine
bounce.
Seed Depth, Placement and Metering 115
Fig. 8.14. An advanced design of no-tillage air drill.
The result is that, although the same
precision metering mechanisms are used
for tillage and no-tillage planters and the
same numbers of seeds need to reach the
ground in a given length of row in both cases,
precise spacing between individual seeds
under no-tillage is more difficult to achieve
than in tillage.
Opener bounce is likely to be greater
under no-tillage. Attempts to qualify the
effect of openers’ bounce were reported in
2004 (Anon., 2004). The tests found that four
conventional vacuum-type precision seed
metering devices of European origin were
all adversely affected by shifting from a
tilled soil surface to an untilled surface and
that the adverse effects increased with
increasing forward speed.
The key question of whether or not
these sources of inaccuracy have a measurable
effect on the final yield of large,
compensatory-growth plants, such as maize,
will continue to be debated (for example,
there is mounting evidence that precision
seeding depth may be more important than
precision spacing, due to inter-plant competition)
but the fact remains that precision
spacing has become an important marketing
objective for machines designed for tilled
seedbeds. Since there is no known agronomic
downside to precision spacing, it makes
sense for designers of no-tillage planters to
attempt to duplicate these levels of precision
spacing as closely as possible if they
want to persuade farmers to make the switch
from tillage to no-tillage.
Summary of Seed Depth, Placement
and Metering
1. Wheat seedling emergence in no-tillage
may decline by approximately 4% for every
10 mm increase in drilling depth below
20 mm and even more beyond 50 mm.
2. Lupin seedling emergence in no-tillage
may decline by approximately 17% for every
10 mm increase in drilling depth below
20 mm.
3. Red clover seedling emergence in
no-tillage will decline markedly at drilling
depths above and below 10–15 mm.
4. The ability of no-tillage openers to
maintain a constant seeding depth is very
important but very demanding.
5. Harder ground, rougher surfaces and
the presence of residues on the surface
accentuate the depth-control challenge
under no-tillage.
6. Because of the large opener downforces
required in no-tillage, seeding depth control
often uses one or more gauge wheels on
each opener.
7. Press wheels are often also used on
each opener to cover the slot.
8. Few no-tillage openers have both gauge
wheels and press wheels, and even fewer
have combined gauge/press wheels.
9. Zero-pressure tyres are a useful adjunct
to gauge wheels.
10. Walking beams are also a useful adjunct
to gauge wheels.
11. Mechanical springs are a poor means
of providing downforce for no-tillage
openers because their forces change with
length.
12. Compressed-air cylinders are sometimes
used to provide downforce but are
seldom a practical option.
13. Removable weights are useful on singlerow
no-tillage drills but are not practical for
multi-row machines.
14. Gas-over-oil systems offer advantages
by using hydraulic cylinders to both
apply the downforce and lift the openers for
transport.
15. Automatic downforce control systems
offer further refinement to gas-over-oil
systems by changing the downforces on
the move in response to changes in soil
hardness.
16. No-tillage openers should provide up
to 500 mm vertical travel compared with a
maximum of 150 mm for tilled soils.
17. Single-pivot drag arms on drills and
planters are less useful in no-tillage than in
tillage.
18. Parallelogram drag arms maintain the
opener angle but are mechanically more
demanding.
19. Lubricated bearings or bushes used for
the pivots on no-tillage openers contribute
to a realistic service life of machines that
operate under difficult conditions.
116 C.J. Baker and K.E. Saxton
20. The function of no-tillage openers in
depositing seed consistently in an uninterrupted
horizontal band in the soil is
important.
21. The function of no-tillage openers
depositing fertilizer in a separate band is
also important, as discussed in Chapter 9.
22. The delivery of bulk-metered seeds to
no-tillage openers is made more demanding
by their large horizontal and vertical
spacing.
23. Air delivery of bulk seeds to no-tillage
openers offers advantages.
24. Single-seed spacing along the row from
precision planters may be compromised in
no-tillage because of seed bounce down
long delivery tubes.
25. No-tillage openers may have special
problems, such as seed flick, seed sticking
to the disc, soil turbulence, residue ‘hairpinning’,
opener bounce, seed bounce and
slot closure.
Seed Depth, Placement and Metering 117
9 Fertilizer Placement
C. John Baker
Simultaneous banding of seed and fertilizer
by the openers is more important in no-tillage
than for tilled soil and follows somewhat
different principles.
It is especially important in no-tillage to
sow fertilizers at the same time as the seed,
but only if the fertilizer can be placed in a
separate band from the seed. Much recent
experience has documented the growth and
yield advantages from fertilizers banded
near the seed at the time of seeding. For
autumn seeding this is often only a ‘starter’
amount of fertilizer, while for spring
seeding it is usually the total seasonal
requirements.
Crop responses to banded fertilizer at
the time of seeding are nearly always larger
in no-tillage than in tillage. There are
several reasons for this.
● Tillage mineralizes organic matter to
release nitrogen and this becomes
readily available to the newly establishing
plants. The downside is that,
because no fertilizer is actually added to
the system, the nitrogen is from ‘mined’,
mineralized, SOM, which depletes this
precious resource cumulatively.
Because mineralization and nitrogen
release are minimal under no-tillage,
young no-tilled plants can appear
nitrogen-deficient, particularly during
early growth. Banding nitrogen fertilizer
alongside the seed during no-tillage
seeding cures the problem.
● Surface residues are often decomposing
about the same time as seeding in
no-tillage. The microorganisms responsible
for residue decomposition temporarily
utilize (‘lock up’) nitrogen during
this process. Even though the nitrogen
they demand may become available
again later in the growth cycle as the
microorganisms themselves die, it is
temporarily made unavailable to young
no-tilled plants.
● Soluble nutrients, nitrogen in particular,
broadcast on to a no-tilled soil surface (as
is common practice in tilled fields) are
often preferentially carried by water flow
down earthworm channels and other
bio-channels (e.g. old root channels),
which largely bypass young plant roots.
In tilled soils, these bio-channels are
destroyed and replaced by a smaller,
more evenly dispersed pore system,
which provides a more uniform infiltration
of water and broadcast fertilizers.
● Under repeated no-tillage, surfaceapplied
nutrients that readily attach to
soil particles, such as phosphorus, accumulate
in a narrow layer near the ground
surface and may not be readily available
to young plants.
© FAO and CAB International 2007. No-tillage Seeding and Conservation
118 Agriculture, 2nd edn. (eds C.J. Baker and K.E. Saxton)
Many of these factors often combine under
no-tillage regimes to make nutrients less
readily available to both seedlings and
growing crops. Thus banding of fertilizers
simultaneously at seeding becomes all the
more important.
Numerous experiments and field observations
have confirmed that the broadcasting
of fertilizers during no-tillage often
results in poor crop responses. Figure 9.1
illustrates a typical field response. A contractor
(custom driller) had been sowing
pasture species in New Zealand with winged
openers into an otherwise fertile field while
simultaneously banding 300 kg/ha of an
N : P : K fertilizer mix alongside (but not
touching) the seed. Near the end of the field
the contractor ran out of fertilizer. The
farmer asked him to carry on sowing seed
alone while he (the farmer) broadcast the
same rate of fertilizer on the remaining area,
which he did. Inadvertently the farmer
had set up a comparison of banded versus
broadcast fertilizer. Figure 9.1 clearly shows
the difference in plant response 8 weeks
after drilling.
Nor are such responses restricted to
grasses. In fact, responses to placed fertilizer
under no-tillage were first identified
with wheat in the USA in the 1980s (Hyde
et al., 1979). Almost every crop and soil
have the potential to show a similar response
to that illustrated in Fig. 9.1. Both
narrow-leaved (monocotyledonous) and
broadleaved (dicotyledonous) plants have
regularly shown similar responses.
Figure 9.2 shows a marked response to
banded fertilizer in France with maize. The
four rows in the centre and left of centre in
the photograph had broadcast fertilizer
applied at the same rate as the placed fertilizer
in all other rows. The differences are
remarkable.
There are two important considerations
when applying fertilizer by banded
placement:
1. Possible toxicity of the fertilizer to the
seeds and seedlings, often referred to as
‘seed burn’.
2. Yield responses of the growing plants
to the placed fertilizer.
We shall discuss these two aspects
separately.
Toxicity
There are three options for applying fertilizer
under no-tillage: (i) broadcasting on
Fertilizer Placement 119
Fig. 9.1. Pasture established by no-tillage in New Zealand with broadcast fertilizer in the foreground
and banded fertilizer in the background at 8 weeks’ growth.
the surface; (ii) mixing with the seed; or
(iii) banding separately from the seed at the
same time as the seed is sown.
Since broadcasting of fertilizer is a
separate operation either before or after
seeding and not a function of the no-tillage
drill or planter, we shall not consider it
further here.
Mixing of fertilizer with seed is a risky
undertaking at any time because of potential
toxic chemical damage to the seed and
seedlings. In tilled soils, a measure of dilution
of the fertilizer with loose soil will
often reduce the risk of ‘seed burn’. But in
an untilled soil, particularly one that is
damp, soil dilution by mixing becomes
minimal.
In general, fertilizer–seed toxicity will
be affected by the following:
● The formulation of the fertilizer. Most
forms of nitrogenous and potassic fertilizers
are likely to ‘burn’ seeds, as well
as some forms of phosphatic fertilizers.
Secondary nutrients such as boron and
sulphur can be particularly toxic.
● The form of the fertilizer. Dry granular
fertilizers are more often placed
directly with the seed than liquid fertilizers.
While it is easier to direct the
liquid placement away from the seed
than the granular, either form will
cause toxicity.
● The age of the fertilizer. ‘Fresh’ superphosphate
may contain free sulphuric
acid, although this dissipates over time
in storage.
● The moisture content of the soil. Dry
soils concentrate the fertilizer salts in
the limited soil solution, which may
damage or kill the seeds by the effects
of reverse osmosis.
Mixing seed and fertilizer and sowing them
together or alternatively allowing them to
mix in the opener or the soil is therefore a
very unsatisfactory way to provide nutrients
for young no-tilled plants. At best,
small amounts of starter fertilizer might be
applied in this manner. Usual upper limits
are considered to be at about 15–20 kg/ha of
nitrogen. But a higher level of risk must be
accepted compared with separate banding
of seed and fertilizer.
Banded fertilizer
For separate banding of seed and fertilizer,
the seed and fertilizer must be placed in different
positions in the soil and remain in
these positions after the opener has passed
and the slot has been closed.
There are three realistic geometric
options. The fertilizer can be placed
directly below, to one side of or diagonally
below and to one side of the seed. Placing
fertilizer above the seed is not a logical
option because this is very similar to
broadcasting.
The ability of no-tillage drills and
planters to simultaneously band seed and
fertilizer without the two coming into contact
with one another is widely recognized
as one of their most essential functions.
Indeed, an informal survey of no-tillage
120 C.J. Baker
Fig. 9.2. The difference between broadcast
fertilizer (left-of-centre four rows) and banded
fertilizer (all other rows) in no-tilled maize
(France).
experts in the USA in the 1980s revealed
that separate banding of seed and fertilizer
was unanimously regarded to be the single
most important design improvement that
should be made to no-tillage openers.
Unfortunately, providing this function has
proved to be an elusive capability for many
machinery manufactures.
Some no-tillage drills and planters
employ two separate openers, one for seed
and another for fertilizer. Others combine
the two openers together into one (often
complicated) ‘hybrid’ opener, while still
others use one dedicated fertilizer opener
between each pair of seed openers. But
there are also modern openers designed
specifically for no-tillage that band seed
and fertilizer in the same slot without compromising
seeding accuracy, row spacing or
residue handling for a wide range of forward
speeds, soils and residue conditions.
Vertical banding versus
horizontal banding
The absence of friable soil makes vertical
separation of seed and fertilizer more
difficult in no-tillage than in tilled soils,
even by successive openers or duplicated
components.
Some drills and most planters in loose
or tilled soils use a leading opener to place
fertilizer at a given depth and then follow
that with a scraper that fills the slot with
loose soil. This in turn is followed by the
seeding opener which opens a new slot that
is either shallower and/or to one side of the
fertilizer slot. Such repeated manipulation
of loose soil is generally not possible or
desirable under no-tillage, so the choice is
to either broadcast or inject the fertilizer as
a separate operation before seeding or
simultaneously seed and place (band) the
fertilizer to one side of the seed by a
separate opener.
Experience with tilled soils suggests
that vertical separation of seed and fertilizer
should be at least 50 mm (known as ‘deep
banding’). Experience with no-tillage, however,
shows that extrapolation of results
from tilled soils requires adjustment for the
nature of the soils and the machine
performance.
The disc version of winged openers
provides a physical barrier between the two
sides of a horizontal slot in the soil, thus
allowing seed to be deposited on one side
and fertilizer on the other to provide
adequate horizontal separation or banding.
As the disc withdraws from the soil it tends
to draw the soil up a little, resulting in
a final horizontal separation distance of
10–20 mm. Figure 9.3 shows the horizontal
separation of seed and fertilizer in an
inverted-T-shaped slot created by a winged
opener.
It is also possible to separate the seed
and fertilizer vertically with this opener by
arranging a long and short blade on the
same side of the disc. Figure 9.4 shows a
prototype winged opener with long and
short blades to provide vertical separation
of seed and fertilizer.
Yet another option exists with this
opener using a long and short blade on
opposite sides of the disc, thus creating
diagonal separation (i.e. both vertical and
horizontal). Figure 9.5 shows an excavated
slot created by a winged opener in which
there is a distinct step down from the seed
shelf to the fertilizer shelf (i.e. diagonal
banding). Figure 9.6 is a diagrammatic representation
of diagonal banding using two
separate disc openers. Similar placement
patterns have recently been achieved with
modified hoe-style openers using configurations
to introduce the seed and fertilizer
at different depths of penetration.
Baker and Afzal (1986) compared the
effects of vertical and horizontal separation
distances of ammonium sulphate
(21 : 0 : 0 : 24) fertilizer from canola (rape,
Brassica napus) seed in an untilled siltloam
soil using a winged opener. Canola
seed is known to be particularly sensitive
to the presence of ammonium sulphate
fertilizer. Figure 9.7 shows seed damage
determined by counts of seedling emergence,
and Table 9.1 shows the seedling
growth.
Figure 9.7 shows that horizontal separation
by as little as 10 mm was equivalent
to vertical separation by twice that distance
Fertilizer Placement 121
122 C.J. Baker
Fig. 9.3. A cross-section of an inverted-T-shaped slot showing the horizontal banding of seed (left)
and fertilizer (right) (from Baker and Afzal, 1986).
Fig. 9.4. A prototype winged opener with long and short blades for vertical separation of seed and
fertilizer (from Baker and Afzal, 1986).
(20 mm) for reduced germination and
emergence.
Table 9.1 shows that not only was there
less seed damage from 20 mm horizontal
separation, there was also a significant
growth advantage for the 20 mm horizontal
separation option compared with mixing of
the seed and fertilizer together or separating
the two by 10 mm either horizontally or
vertically. Neither the horizontal nor the
vertical separation by 20 mm was significantly
different from where no fertilizer had
been applied, which confirmed that no seed
damage had occurred.
Afzal (1981) also compared the effectiveness
of horizontal separation by a
winged opener in tilled and untilled soils,
to gauge the extent to which results from
tilled soils could be safely extrapolated to
untilled soils. Table 9.2 shows the results.
At all three sampling dates (10, 15 and 20
days after sowing), the no-tilled soil contained
more plants than the tilled soil, indicating
that some seeds in the tilled plots
had either been killed by the fertilizer, or
had failed to germinate for other reasons.
An explanation for the effects in
Table 9.2 seems to lie in the fact that, with
Fertilizer Placement 123
Fig. 9.5. Diagonal separation of seed and fertilizer in the soil (fertilizer below the seed towards
bottom of photo) using a winged no-tillage opener with an elongated blade on one side.
Fig. 9.6. A diagrammatic
representation of diagonal fertilizer
banding with two angled disc openers.
124 C.J. Baker
Fig. 9.7. Effects of the position of fertilizer placement, relative to the seed, on seedling emergence
of no-tilled canola (from Baker and Afzal, 1986).
Number of true leaves Plant height (mm) Plant weight (g)
No fertilizer 4.1 ab 63 ab 46 ab
Seed and fert. mixed 3.3 b 36 b 22 b
Horizontal separation by
10 mm 3.3 b 34 b 19 b
20 mm 4.3 a 71 a 80 a
Vertical separation by
10 mm 3.3 b 38 b 25 b
20 mm 4.2 ab 60 ab 54 ab
Unlike letters in a column denote significant differences (P < 0.05).
Table 9.1. Effects of method of fertilizer placement on seedling performance of no-tilled canola.
Days after sowing
Establishment method 10 15 20
No-tillage (plants/square metre) 25.1 a 50.7 a 55.2 a
Conventional tillage (plants/
square metre)
19.4 b 41.6 b 44.8 b
Increase of no-tillage over
conventional tillage
29% 22% 23%
Unlike letters in a column denote significant differences (P < 0.05).
Table 9.2. Effects of tillage and no-tillage on horizontal separation of canola seed and
fertilizer in the slot.
this particular opener design, the central
disc cuts a thin vertical slot in the soil
50–75 mm deeper than the horizontal
shelves on which the seed and fertilizer are
placed. In an untilled soil, the integrity of
this disc cut remains more distinct than in a
tilled soil, where the friable nature of the
soil allows soil to collapse into the disc-cut
zone as the disc withdraws from the soil.
It is thought that this disc cut, in an
untilled soil, effectively interrupts solute
movement from the fertilizer, which might
otherwise reach and damage the seed or
seedling roots. It is also possible that the
high humidity in the inverted-T slot in an
untilled soil helps prevent reverse osmosis,
which is one of the mechanisms by which
seeds are damaged by high salt concentrations
in dry tilled soils (see Chapters 5 and
6). Because the general humidity of a tilled
soil is lower than that of an untilled soil,
due to the artificially high porosity and the
absence of surface residues, even the
inverted-T-shaped slot is unable to maintain
a high humidity zone around the seed
when operating in a tilled soil.
Another important point in the tilled/
no-tilled soil comparison is that the effects
of separating the seed from the fertilizer are
most apparent as the soil became drier.
Collis-George and Lloyd (1979) had earlier
noted that, in tilled soils, dryness tended to
result in more fertilizer damage to seeds
than where the soil was moist. Baker and
Afzal (1986) examined whether or not this
trend extended to untilled soils, using a
winged opener.
Their results, shown in Table 9.3, indicate
that plants suffered with both vertical
separation and mixing together when the
soil became dry, but these were equivalent
to the other treatments in the moist soil.
The only treatment that almost ignored the
moisture status of the soil was the horizontal
separation within an inverted-T-shaped
slot. This may have been partly the result of
the high humidity this slot maintains and
partly the result of the disc cut. The result is
that the optimum horizontal separation distance
within an inverted-T-shaped slot was
less than the distance commonly recommended
for vertical separation by other
openers and for tilled soils.
Field experience has shown that the
particular disc version of the winged
opener used in these experiments is equally
well suited to separating seed from liquid or
gaseous fertilizers as it is to separating it
from dry powdered and granulated forms of
fertilizer.
In two separate experiments (C.J. Baker,
unpublished data), the author found that
the upper limit of dry urea (46 : 0 : 0 : 0)
application with this opener, sowing maize
in 750 mm spaced rows, was about
200 kg/ha of urea (92 kg/ha/N), equivalent
to 15 g urea per metre of sown row, before
seed damage was detectable. Field applications
of 780 kg/ha of 30% potassic superphosphate
(0 : 6 : 15 : 8) with peas in
150 mm rows (117 kg/ha/K) have also been
achieved with this no-tillage opener with
no measurable toxicity damage to seed
germination when compared with no
fertilizer.
K.E. Saxton (unpublished data) also
tested the ability of the same winged opener
to effectively separate wheat seed from toxicity
damage arising from the use of a range
of rates and two forms of nitrogenous fertilizers
sown in 250 mm rows in the USA. He
found no detrimental effect on the seed
from applying either dry urea (46 : 0 : 0 : 0)
or liquid ‘aqua’ (ammonium hydroxide
Fertilizer Placement 125
Horizontal separation by 20 mm Vertical separation by 20 mm Mixed together
Dry soil Damp soil Dry soil Damp soil Dry soil Damp soil
89 81 64 90 58 85
Table 9.3. Effects of position of fertilizer placement and soil moisture status on germination of
no-tilled canola (germination %).
solution in water: 40 : 0 : 0 : 0) at concentrations
of up to 140 kg/ha of nitrogen.
Operators in New Zealand commonly
apply up to 400 kg/ha of high-analysis
fertilizer mixes (which sometimes include
boron and/or elemental sulphur) in the field
with this opener with no measurable effect
from ‘seed burn’ but with substantial positive
growth and yield responses (Baker
et al., 2001).
Although horizontal separation appears
to be somewhat more beneficial than vertical
separation in most instances, a range
of vertical separation systems have been
designed. Hyde et al. (1979, 1987) reported
attempts to separate seed and fertilizer vertically
with a single opener by modifying
a hoe opener so that it deflected soil back
over the fertilizer before the seed exited the
opener. The deflecting action, however,
was dependent on forward speed and soil
moisture conditions, especially plasticity.
In favourable conditions, its crop yield
performance was comparable to horizontal
separation by winged openers.
One solution that allows vertical separation
of seed and fertilizer in no-tillage to
be largely independent of soil moisture
conditions is the use of slanted double disc
openers. The leading (fertilizer) opener cuts
a slanted slot and places the fertilizer at
its target depth. The seed opener, which
follows, is positioned either vertically or at
the opposite slant and shallower, thereby
placing the seed in the undisturbed soil
above the fertilizer. This option appears to
be effective but the downforces required to
make two double disc openers penetrate the
soil for each row limits it to reasonably soft
soils. Figure 4.8 shows two slanted double
disc openers so configured.
Another, more laborious but effective,
method is to pre-drill the fertilizer as a separate
operation to drilling of the seed at a
shallower depth, and this can be achieved
with virtually any design of opener.
Retention of gaseous fertilizers
Inverted-T-shaped slots are known to retain
water vapour in the slot (see Chapters 5
and 6). It is possible that this slot also
retains volatile gases from nitrogenous fertilizers
(especially ammonia) within the
slot in a similar manner to water vapour.
It is well known that soil injection of
both organic (animal waste) and inorganic
forms of nitrogen as gas or liquid leads to
problems with ammonia gas volatilizing and
escaping into the atmosphere. With disposal
of animal waste using knife-type openers
(U-shaped slots), this is often overcome by
deep (0.5 m) injection. Inverted-T-shaped
slots also offer the option of shallow injection
of this material (Choudhary et al.,
1988b).
During the no-tillage drilling of seeds,
simultaneous deep injection of inorganic
nitrogen is impractical because of the limitations
on depth of placement and available
tractor power. The result of simultaneous
shallow placement has usually been a
noticeable smell of ammonia at drilling as it
escapes from the sown slots.
With the winged opener, less ammonia
smell is evident, indicating entrapment of
the valuable fertilizer within the slots. This
was first noticed in the field in the USA by
farmers using a winged opener. They were
intrigued by the fact that the farm dogs ran
along behind the drill. This apparently did
not occur with other drills because the
escape of ammonia from the soil immediately
behind the drill made an unpleasant
environment for the dogs.
Crop Yield
As previously discussed, broadcast fertilizers
on no-tilled fields are often infiltrated
by water moving into preferential flow
paths and bypassing the early plant roots, or
those constituents that bind to the soil
remain on the soil surface. In contrast, tilled
soils have more diverse flow paths through
their microporosity and blend those binding
constituents within the tilled zone. As a
result, while broadcasting of fertilizers has
been practised successfully for years with
crops grown in tilled seedbeds, under notillage
the same crop responses to broadcast
126 C.J. Baker
fertilizer cannot be relied upon. Hyde et al.
(1979) highlighted the problem in the
Pacific Northwest of the USA, and a longterm
experiment conducted by the authors
over a 6-year period in New Zealand also
illustrated the problem (Baker and Afzal,
1981).
In the New Zealand experiment, the
scientists compared the continuous growing
of summer maize, sown with a winged
opener, on the one hand, into untilled soil
and, on the other hand, into a conventionally
tilled seedbed. It also coincided with
some important technological developments
of winged openers, which had an
impact on the experiment.
Figure 9.8 illustrates the first 5 years of
the maize yield results. To eliminate seasonal
variations in yield, conventional tillage
was given the arbitrary value of 100%
each year and no-tillage was compared with
it on a percentage basis. The seed was sown
into inverted-T-shaped slots on all occasions
with Class IV cover.
In year 1 no fertilizer was applied,
either at planting or after the crop became
established. The crop relied solely on the
already high fertility of the soil, which had
been under intensive pasture for 20 years.
The maize yield under no-tillage was not
significantly different from that under
tillage.
In year 2 again no fertilizer was used.
By this time, however, the advantages of
mineralization, which is enhanced by the
tillage process, had become evident. Only
slow mineralization rates occur under notillage
because of the absence of soil disturbance.
As a result, the no-tillage maize yield
was only 35% of that under tillage.
In year 3 a comprehensive NPK starter
fertilizer (10 : 18 : 8 : 0) was surface-applied
at 300 kg/ha by broadcasting on to all plots.
At that time, simultaneous banding of seed
and fertilizer by winged openers was not
possible without risk of seed damage. The
seed was sown with the simple original
winged opener and mixing of seed and fertilizer
together was not considered a viable
option.
The disc version of the winged opener,
which allows simultaneous banding, had
not by then been invented. None the less,
the surface-applied fertilizer lifted the yield
under no-tillage to 60% of that under
tillage.
In year 4 it was decided to apply a
greater amount of broadcast NPK fertilizer
than in year 3 (400 kg/ha) to both treatments
to try to raise the no-tillage yield still
further. Doing so had the opposite effect,
however, and the no-tillage yield of maize
fell to an all-time low of only 30% of the
yield under tillage.
Fertilizer Placement 127
Fig. 9.8. Relative dry matter (DM) yield of no-tillage compared with tillage as affected by fertilizer
application on no-tillage maize yields over a 5-year period (from Baker and Afzal, 1981).
Year 5 coincided with the development
of the disc version of the winged opener concept,
which, amongst other things, allowed
seed and fertilizer to be banded simultaneously
with 20 mm horizontal separation
in inverted-T-shaped slots.
The effect on the yield of no-tilled
maize was immediate and spectacular. It
raised the yield to again be not significantly
different from the tilled yield.
In year 6 the experiment was altered to
directly compare banded and broadcast
fertilizer application under tillage and notillage
and to check if the year 5 results
were repeatable. Indeed, they were.
Table 9.4 presents the results for year 6.
Clearly, the no-tilled soil benefited more
from banding of fertilizer than the tilled
soil. The final yields of the two methods
with banded fertilizer were not significantly
different.
Perhaps just as important were the
yields of maize obtained from plots that had
not received any fertilizer in the entire
6-year period. Although the unfertilized
yields from both the tilled and untilled soils
were poor in comparison with the fertilized
plots, the enhanced mineralization that had
occurred in the tilled soil each year produced
plants almost three times as big as
those under no-tillage. This mineralization,
however, represents a ‘burning out’ of the
SOM, with associated loss of soil quality,
and is the reason why tillage is no substitute
for no-tillage where fertilizers are
applied correctly, in terms of both sustainability
and crop yield.
An on-farm comparison was made in
2004 by a New Zealand farmer. He chose 11
fields and sowed a forage brassica crop into
a randomly chosen selection of the fields
over a 17-day period with two different
no-tillage drills (M. Hamilton-Manns, 2004,
unpublished data).
One drill was equipped with vertical
triple disc openers. The triple disc openers
had wavy-edged leading discs, which reduce
the compacting effects normally associated
with such openers. But they were not capable
of banding fertilizer, so diammonium
phosphate (DAP) fertilizer was broadcast at
300 kg/ha. The other drill was equipped
with the disc version of winged openers,
which banded the same amount of fertilizer
20 mm to one side of the seed at the time of
seeding. Soil moisture conditions were not
limiting and seedling germination was adequate
with both drills.
The fields drilled with triple disc openers
and broadcast fertilizer yielded, on average,
7069 kg dry matter (DM)/ha. The fields
drilled with winged openers and banded fertilizer
yielded, on average, 10,672 kg DM/ha.
While it cannot be said with certainty
that the entire 51% average difference was
the result of banded fertilizer alone (there
may also have been opener differences),
there is little doubt that most of the difference
was due to fertilizer banding, and the
heavier crops were worth, on average,
US$468/ha more than the smaller crops.
Banding options
We have already seen that the need to band
fertilizer beneath the soil without ‘burning’
the seed is greater under no-tillage than
with tilled soils. Mixing of seed and fertilizer
risks ‘seed burn’.
Recourse to ‘skip-row’ seeding, in
which every third opener sows only fertilizer
in order to fertilize the two seeded rows
either side of it (Little, 1987), has not been a
feasible alternative either, although certainly
better than broadcasting. Choudhary
et al. (1988a) showed only mixed success
with the ‘skip-row’ option, even when sown
in narrow (150 mm) rows. Table 9.5 shows
their results.
The ‘skip-row’ treatment produced the
lowest fertilized barley yield (2072 kg DM/ha)
but was equal to all other treatments when
128 C.J. Baker
Fertilizer
placed
Fertilizer
broadcast
No fertilizer
applied
No-tillage 10,914 4,523 1,199
Tillage 10,163 5,877 2,999
Table 9.4. Effects of fertilizer placement on yield
of maize (DM yield kg/ha) in the sixth year of a
6-year experiment.
fodder radish was sown. In the latter case
mixing of the seed with the fertilizer gave
the poorest yield (2809 kg DM/ha). All other
treatments were not significantly different.
Two other important points are evident
in Table 9.5. The results are the mean of two
soils, one of which was a fine sand, in which
few, if any, preferential flow channels were
present because of the exceedingly friable
nature of the soil. Thus, even in its untilled
state, surface-applied nitrogen fertilizer would
have flowed more or less evenly through
such a profile as if it had been tilled and
showed less difference in favour of banding
than where the soil was more structured.
The other point is that one of the
fertilizer/seed combinations used in this
experiment (DAP and barley) was not particularly
damaging to barley seed. Consequently,
mixing of barley seed and fertilizer
together showed no disadvantage. On the
other hand, mixing of the DAP fertilizer
with the more susceptible brassica crop
showed results similar to those of Afzal
(1981) and Baker and Afzal (1986), who had
used an even less compatible mix (canola
and ammonium sulphate).
There is no evidence from any experiments
conducted by the authors that greater
amounts of fertilizer are needed under
no-tillage. That which is applied just needs
to be used more effectively by banding it
alongside the seed. In fact, data from seven
different experiments involving wheat
(Triticum aestivum), drilled with double
disc openers in a skip-row configuration
(where every third row was sown with
fertilizer only, at 100 mm depth), compared
with horizontal separation by 20 mm with
a drill equipped with winged openers,
showed that fertilizer rates could actually
be reduced with the latter openers (Saxton
and Baker, 1990). Figure 9.9 shows the
results.
On average, the winged openers showed
a 13% increase in wheat yield compared
with the skip-row drilling with double disc
openers. Until then, that particular skiprow
configuration had out-yielded all other
methods with which it had been compared
in the USA.
Not only did the plants sown with horizontal
banding out-yield those sown with
the skip-row method, but further measurements
showed that the plants had been more
vigorous from the outset. The improved vigour
is likely to have been partly because of
the positioning of the fertilizer and partly
because of the high-humidity environment
in which the seedlings developed beneath
the ground in the horizontal (inverted-Tshaped)
slots.
Table 9.6 shows analyses of the carbon
and nitrogen contents of seedlings grown
by these two fertilizer banding methods.
Figure 3.1 had earlier shown the contrasting
development of the seedlings in which the
heavier and more fibrous nature of the root
systems (more root hairs) from the horizontal
banding and inverted-T-shaped slot was
clear. Apparently, both the carbon and
nitrogen levels were higher in the plants
sown by the winged openers with horizontal
banding of fertilizer compared with
Fertilizer Placement 129
Barley grain DM
yield (kg/ha)
Fodder radisha (whole plant)
DM yield (kg/ha)
No fertilizer 1889 b 3240 ab
Horizontal separation by
20 mm
2580 a 3763 a
Fertilizer and seed mixed 2538 a 2809 b
Broadcast fertilizer 2432 a 3543 a
Skip-row separation 2072 b 3526 a
Unlike letters in a column denote significant differences (P < 0.05).
aBrassica napus L.
Table 9.5. Effects of fertilizer application method on yield of two no-tilled crops.
those sown with the double disc opener and
‘skip-row’ fertilizer application.
Even where vertical banding of seed
and fertilizer has been accomplished using
a single opener, no clear advantage has yet
been shown for this option.
Further, the technical difficulty of
achieving satisfactory vertical banding in a
wide range of conditions with a single
opener makes implementation on a field
scale unreliable. The problem is that, to
achieve vertical separation, the fertilizer is
usually drilled first at a greater depth than
the target depth for the seed. In tilled soils it
is relatively easy to induce soil to fall on to
the fertilizer before the seed is sown. But in
untilled soils this is much more difficult to
achieve, particularly when the soil is damp
and ‘plastic’. For this reason, horizontal
separation has become a more ‘fail-safe’
alternative since effective separation is not
affected by soil looseness, surface cover or
operating speed.
A comparison of horizontal banding
(winged opener) and vertical banding (prototype
hoe opener with a deflector to scoop
soil on to the fertilizer prior to deposit of the
seed) was made over several years by the
authors. The results are shown in Fig. 9.10.
The figure shows that the winged
opener with horizontal banding produced
a greater yield in the first year of spring
wheat (SW 87) and perhaps in the final year
of winter wheat (WW 89), but there were
no differences in yield in the other three
seasons.
130 C.J. Baker
Fig. 9.9. Wheat yield comparisons from no-tillage using two different fertilizer banding options
(from Saxton and Baker, 1990).
Opener type Field no. Carbon (% DM) Nitrogen (% DM)
Winged opener (inverted-T,
horizontal banding)
1
2
38.00
38.60
4.16
4.70
Mean 38.30 4.43
Double disc opener (V-shaped
slot, skip-row application)
1
2
36.50
34.69
4.00
3.83
Mean 35.60 3.92
Table 9.6. Carbon and nitrogen contents of no-tilled wheat seedlings sown with two
different openers.
A long-term double cropping experiment
in Australia compared yields of soybean
crops sown under no-tillage and tillage
for 14 years using winged openers (Grabski
et al., 1995). For the first 2 years (1981/82
and 1982/83) the conventional tillage yields
were superior, presumably because of the
previous history of tillage. But for the following
12 years the no-tillage treatment was
never bettered and averaged 30% higher
yield of soybean than conventional tillage.
How close should banded fertilizer
be to the seed?
Ferrie attempted to answer this question in
Illinois, USA, in 2000. His results were
reported by Fick (2000). Ferrie compared
several diagonal distances of separation of
starter fertilizer from maize seed sown with
double disc openers, ranging from 90 mm
deeper than and 50 mm to one side of the
seed to 15 mm deeper than and 20 mm to
one side of the seed. He concluded that, in
terms of crop responses, ‘the closer the
starter was to the seed the better’, provided
that the fertilizer was not actually mixed
with the seed and the action of banding the
fertilizer did not disturb the accurate placement
of the seed. The treatment with the
greatest separation distance actually produced
no measurable yield response to the
starter fertilizer at all.
Ferrie also pointed out that slot wall
compaction could have an effect on the
ability of juvenile roots to access the fertilizer,
especially in clay soils. He felt that, in
such soils, even a narrow knife opener
could cause problems.
Dianxion Cai (1992, unpublished data)
tested two options for placing dry and liquid
nitrogenous fertilizers at increasing
rates of applied N, using winged openers
and drilling wheat seeds 25 mm deep. The
two options were: (i) standard horizontal
banding 20 mm to one side of the seed (i.e.
the fertilizer was also drilled 25 mm deep);
and (ii) diagonal banding in which the
fertilizer was banded 20 mm to one side of
and 13 mm deeper than the seed (i.e. the
fertilizer was drilled 38 mm deep). Figure
9.11 shows the effect on plant stand and
Fig. 9.12 shows the resultant crop yields.
From Figs 9.11 and 9.12, it is apparent
that the effects on seedling emergence
(stand) were similar to the effects on yield,
demonstrating the importance of initial
plant population for final yield. In both
experiments the horizontal banding (25 mm)
produced more plants and heavier crops
than the diagonal banding (38 mm) with
both urea and aqua. These differences
became most pronounced at an application
rate of about 120 kg N/ha. At higher application
rates, while the differences remained
largely unaltered, both the plant stands and
crop yields began to decline, possibly
because of fertilizer toxicity. The decline of
both plant stand and crop yield at the high
application rates (160 kg N/ha) used in
these experiments was considered to be of
no consequence because these application
rates were well in excess of normal application
rates of nitrogen in any form (160 kg
N/ha is equivalent to 350 kg urea or 400 kg
aqua/ha).
Fertilizer Placement 131
Fig. 9.10. No-tillage wheat yields from vertical
banding of fertilizer with a hoe opener and
horizontal banding with a winged opener.
Conclusion
One of the more noteworthy advances in
no-tillage technology has been to develop a
machine with the capability to separate fertilizer
from the seed in horizontal bands
and effectively entrap volatile forms of
nitrogen in the slot. At the same time, these
132 C.J. Baker
Fig. 9.11. Wheat stand responses to horizontal and diagonal banding of two forms of nitrogenous
fertilizer separated from inverted-T-shaped slots.
Fig. 9.12. Wheat yield responses to horizontal and diagonal banding of two forms of nitrogenous
fertilizer separated from inverted-T-shaped slots.
openers maintain the effectiveness of the
separation function without being materially
altered by forward speed, soil type, soil
moisture content or the presence or absence
of surface residues. From a field perspective,
farmers find it easier to identify with
this single factor, among all others, when
assessing the performance of no-tillage versus
tillage, and even when assessing the
merits of competing no-tillage systems and
machines.
It is interesting to speculate how many
experiments and field observations showing
poor yields for no-tillage crops have
been the result of opener inability to
adequately band the fertilizers.
Summary of Fertilizer Placement
1. Less nitrogen is available by organic
matter mineralization under no-tillage than
under tillage, making nitrogen application
particularly important at drilling under
no-tillage.
2. Some temporary nitrogen ‘lock-up’ may
also occur under no-tillage as soil bacteria
decompose organic residues.
3. Broadcast fertilizers are less effective in
no-tillage than in tillage because soluble
nutrients often bypass roots by infiltration
occurring in preferential channels created
by earthworms and decayed roots.
4. ‘Deep-banding’ of fertilizers at drilling
is less effective or necessary in untilled
soils than in tilled soils.
5. Fertilizer close to the seed is better than at
a distance, so long as the two are not mixed.
6. Horizontal separation between seeds
and fertilizer at distances as small as 20 mm
have been more effective in no-tillage than
vertical separation by any distance.
7. Relatively few no-tillage openers provide
effective seed and fertilizer banding
with a proper distance or direction.
8. Of those no-tillage openers that do provide
effective separation, horizontal separation
is preferable to vertical separation.
9. Where no-tillage openers are incapable
of separating seed from fertilizer, other
options include:
● Drilling every third row with only fertilizer
(‘skip-row’ planting).
● Mixing seed and fertilizer together in
the slot.
● Doubling the number of openers on a
drill so as to provide separate fertilizeronly
openers in addition to seed-only
openers.
● Surface broadcasting of the fertilizer.
● Drilling seeds and fertilizer as two
separate field operations at different
depths.
10. Most double disc openers are incapable
of banding fertilizer separately from the
seed with a single opener.
11. Some angled disc openers have provided
a fertilizer-banding capability.
12. One version of winged openers with a
single disc effectively separates seed and
fertilizer horizontally or diagonally.
13. Crop yields with winged openers have
been good when using horizontal separation
of seed and fertilizer, due to improved
seed/seedling micro-environment and
fertilizer response.
14. Only recently designed hoe openers
separate seed and fertilizer in any direction.
15. Two disc openers (double or angled)
slanted in opposite directions may be capable
of providing vertical separation of seed
and fertilizer.
Fertilizer Placement 133
10 Residue Handling
C. John Baker, Fatima Ribeiro and Keith E. Saxton
Successful no-tillage openers not only
handle surface residues without blockage
but also micro-manage these residues so that
they benefit the germination and seedling
emergence processes.
The second most valuable resource in
no-tillage is the residue left on the ground
surface after harvest of the previous crop.
The only resource more valuable than residue
is the soil itself – in its untilled state.
Unfortunately, the history of tillage is
littered with descriptions of methods for
disposing of residues so that they do not
interfere with the operation of machinery.
In tillage, surface residues have been
regarded as a major nuisance and therefore
have often been referred to as ‘trash’. Those
who take no-tillage seriously have dispensed
with the term ‘trash’ in favour of the
term residue. Trash is something unwanted.
Residue is something left over, but in this
case wanted and useful.
Before considering how well various
openers and machines handle or manipulate
surface residues, it is necessary to identify
the various forms that residue can take
(Baker et al., 1979a). Then it will be appropriate
to look at how the residues should
be macro-managed on a field scale
(Saxton, 1988; Saxton et al., 1988a, b; Veseth
et al., 1993) and finally at the options for
micro-managing residues in, around and
over the slot zone (Baker and Choudhary,
1988; Baker, 1995).
The Forms that Residues can Take
Short root-anchored standing vegetation
Pasture (either growing or recently
killed by herbicide)
Short root-anchored pasture is commonly
encountered by no-tillage drills designed
for pasture renovation or renewal in intensive
animal grazing agricultural systems
and for crop establishment in integrated
crop/animal systems. In such systems, animal
management can usually be sufficiently
controlled to allow deliberate intensive
grazing of selected fields prior to drilling,
thus reducing the length of grass and therefore
the residue-handling demands on such
machines. This allows relatively inexpensive
drills to be used for such conditions.
Short standing pasture usually presents
few residue-handling problems as the vigorous
root anchorage and firm soil beneath
the plants allows even a ‘rigid’ tine or shank,
without a pre-disc, to burst reasonably
cleanly through it. If the pasture has been
recently killed, the time-interval between
© FAO and CAB International 2007. No-tillage Seeding and Conservation
134 Agriculture, 2nd edn. (eds C.J. Baker and K.E. Saxton)
spraying and drilling can have a profound
effect on the handling properties of this
residue. As decomposition starts soon after
death of the plant, the material becomes
progressively weaker and more likely to
break away from its anchorage. At an
advanced stage of decay, it may break away
from the soil anchorage altogether and start
to behave more like loose-lying residue
than short anchored residue and therefore
be more prone to causing blockage. Sometimes
it pulls free in large pieces.
Pasture plants that have stoloniferous
or rhizomatous growth habits (i.e. with horizontal
and/or underground connecting
stems), even though they might be grazed
short by animals, present a different problem,
since their creeping habit makes them
likely to become entangled in non-disc-type
openers. At least a pre-disc is essential for
satisfactory handling of such residues with
tine or chisel openers.
Short clean crop stubble after direct-heading
with a combine harvester and
baling of the straw
Clean crop stubble that has negligible loose
straw lying on or amongst it offers only moderate
residue-handling problems because
the standing plants can usually be pushed
aside by relatively unsophisticated no-tillage
openers. In common with pasture plants, the
key element is the anchorage offered by the
root systems. The time interval between
harvesting and drilling and the intervening
weather will also influence the level of
decay that has set in by the time drilling
takes place. In the case of crop stubble,
however, because harvesting normally
takes place at a dry time of the year, the
onset of decomposition may be slower than
with pasture plants.
Standing stubble has important additional
functions in no-tillage systems that
experience snow and freezing winters or
in which the crop is swathed prior to
harvesting.
Where swathing takes place, long stubble,
especially in narrow drill rows, will
hold the cut swathe off the ground, which
aids drying and makes harvesting easier as
it aids the pickup mechanisms on combine
harvesters compared with when the swathe
lies close to the ground.
Where snow is expected, stubble holds
the snow from blowing away. Snow, in
turn, provides effective thermal insulation
of the soil beneath and may be responsible
for maintaining soil temperatures some 10°
to 15°C higher than in soils that have no
snow cover and are allowed instead to
freeze (Flerchinger and Saxton, 1989a, b). In
this respect, long stubble is better than short
stubble (see below).
In either case, at the end of a cold winter,
when such soils are drilled, stubble that
has endured the cold months is usually
brittle, though often it has not actually
decayed much. It may break off at ground
level, but due to its shortness will seldom
present major residue-handling problems
for no-tillage drills. On the other hand,
no-tillage systems increasingly require that
the full amount of residue disgorged from
combine harvesters (including the threshed
straw as well as the standing stubble) remains
on the ground over the winter in such
climates. This combination presents quite
another problem as far as residue handling is
concerned, which will be discussed later.
Standing stubble also has an important
function in dry climates, by reducing wind
velocity at the soil surface, which significantly
reduces drying and soil movement.
In windy conditions, standing stubble may
protect young seedlings sown between
the stubble rows from being blasted by
wind-blown sand and other soil particles.
In Australia, for example, planting between
the rows of tall stubble offers wind protection
to the new plants, while, in England,
long stubble has another value, that of
camouflaging wildlife, such as pheasants.
Since many farmers in that country rate the
commercial shooting of pheasants as an
important source of farm income, no-tillage
offers an opportunity through stubble retention
for an extended game-shooting period
that was not possible with tillage.
In tropical climates, tall standing stubble
can result in etiolation of the new crop.
But short standing residues lead to more
vegetative material entering the combine
Residue Handling 135
harvester, resulting in a higher power
requirement, more fuel consumption or
decreased field capacity.
For all of these reasons, there has been
recent interest in the use of stripper headers
in association with no-tillage because such
harvesting devices maximize the length of
the standing stubble.
Tall root-anchored standing vegetation
Tall grass, sprayed-off cover crops and tall
clean stubble (300 mm and longer),
together with bushy weeds, present somewhat
greater problems than short vegetation,
even with root anchorage, but less
than lying straw. There is a critical height
above which each of these plants will collapse
in the pathway of no-tillage openers
(or simply over a period of time), at which
point the residue behaves more like lying
straw than standing stubble. Taller material
may also trap a more humid microenvironment
within, with the result that
decay of the bases of the straw may be initiated
more quickly than with short stubble
and breakage is more likely.
Figure 10.1 shows the effect of drilling
with the disc version of a winged opener
through a partially standing matted legume
crop 0.75 m high that had been sprayed.
It is not common to drill into such very
tall residue; not only because of the
spatial constraints, but because it is difficult
for seedlings to obtain sufficient
light during early development to emerge
satisfactorily.
Lying straw or stover
Detached stalk material, of any length, presents
the most difficult residue-handling
problems for no-tillage drills but is also a
very valuable biological resource unique to
no-tillage. Where such residues lie on firm
ground (e.g. after a no-tilled crop has been
harvested, or even when hay has been fed
directly on to an established pasture and
not fully consumed by animals), there
will be less tendency to block no-tillage
openers than where the residues lie on
softer ground. Similarly, if the residues
remain dry and brittle, they will be easier
to handle and cut than where they have
136 C.J. Baker et al.
Fig. 10.1. The effects of drilling with the disc version of winged openers into heavy partially
standing residue.
become damp. Often dampness is a function
of both the amount of straw (yield
of the crop) and the weather. Heavy residues
may generate their own dampness
and increase in temperature from bacterial
action.
The immediate history of the field may
also be important. If the previous annual
crop was established into tilled soil, for
example, the soil background against which
disc components of no-tillage openers will
need to push to shear the straw, will be
softer than if the previous seedbed had been
untilled. This ‘anvil effect’, of course, will be
influenced by soil type, which has an important
influence on the effectiveness of some
residue-handling mechanisms and presents
farmers with some difficult choices when
converting from tillage to no-tillage.
For example, a no-tillage machine that
is good at drilling into residues previously
established in a tilled seedbed (during the
changeover period) may not be the best
machine for drilling into residues previously
grown in an untilled seedbed. Further, some
farmers believe (usually erroneously) that
they will still need to occasionally till their
soil even under a predominantly no-tillage
regime. There may be little logical basis for
this belief, but it will none the less influence
the farmer’s choice of machine, perhaps
to the detriment of the true no-tillage phase.
The problem seldom exists when drilling into
pasture because it is unusual for pasture to
have been established for less than 12 months,
during which time even a previously tilled
soil will have consolidated again.
Fortunately, some no-tillage openers
are equally well suited to soft and firm (or
even hard) soils. The function of most
tine- or shank-type, power till and winged
openers is relatively unaffected by soil
softness or firmness (except for downforce
or power requirements), but those that tend
to hairpin residue into the slot (double
disc, angled flat disc and angled dished
discs) have their hairpinning tendencies
accentuated by softer soils. On firmer soils,
they are more likely to shear the straw
(which is desirable) than to push it bent
over into the slot (which is undesirable). In
firm soils, however, some openers are also
more likely to compact the soil in the slot
zone.
Lying residues have no anchorage to
the ground and are therefore very easily
gathered up to become entangled in ‘rigid’
machine components. Firmer ground provides
greater friction (traction) for discs that
may operate in conjunction with rigid components,
ensuring that they keep revolving
when they encounter lying residues. Some
discs are especially shaped to further assist
traction. Wavy-edged discs and notched or
scalloped discs are cases in point. Even so,
if the height of the lying straw is above the
axle height of an approaching disc, it is
likely to stall the disc, causing sledging and
blockage. This is accentuated by dampness
under the straw, especially if such dampness
results in partial decay close to the
ground. The decaying straw can become
quite slippery on the ground and will often
slide ahead of a disc, rather than allow the
disc to grip and ride over or cut through it.
Straw lying amongst standing stubble is less
likely to slip than where it is lying on bare
ground.
This sliding tendency is dependent to
some extent on plant species. It is also soildependent
and obviously weather-dependent.
For example, pea straw becomes particularly
slippery when partially decayed, especially
on firm untilled soil, while most
cereal straws do not. Sparse straw, such as
soybean, canola, cotton or lupin, is less
likely to remain damp long enough to promote
decay close to the ground than crops
that produce heavier vegetative growth.
Further, the rigidity of the cut stubble of
these somewhat woody crops helps prevent
sliding of the lying residue.
Numerous methods have been devised
to handle lying straw. Some of these are
summarized below. The successful methods
almost invariably involve openers
where discs are used, either simply as the
opener itself or where the discs assist
the operation of other rigid components,
such as winged blades, chisels or tines.
In both cases, discs have become a common,
though not exclusive, component of
no-tillage openers designed for the handling
of residues.
Residue Handling 137
Management of Residues on a
Field Scale
Macro-management refers to the way in
which the residues are managed on a field
scale. Their management is discussed separately
for: (i) large field-scale no-tillage; and
(ii) small-scale no-tillage. But in either case,
surface biomass, whether from killed cover
crops or harvested residues, plays a key role
in no-tillage systems. For any no-tillage
system (large or small), the handling of
residues should:
1. Assist (or at least not hinder) the passage
of no-tillage openers.
2. If possible, contribute to the biological
functions of the openers.
3. Ensure that the residues decompose
and add to soil carbon but at the same time
remain on the soil surface long enough to
protect the soil from erosion, keep the soil
cool in tropical climates, retain soil moisture
and suppress weeds;
4. Ensure that the residues do not compete
with the sown crop.
These are demanding and sometimes competitive
requirements, and compromises are
often necessary. For example, tine (shank)-
or knife-type openers do not handle residues
well, so some farmers resort to burning
or otherwise removing the residues to avoid
blockages when drilling a field. But this
compromises some of the other listed functions.
For this and other reasons, the burning
of residues is banned in several
countries, although up to 45% of the biomass
will be in the roots that remain even
after burning.
In this respect, it is interesting to note
that it makes little difference whether harvested
residues are baled, burned or buried
in terms of the amount of carbon they provide
for the soil (see Chapter 2). Unless they
are left to decompose on the soil surface,
much of the carbon content of the aboveground
plant residues will be lost from the
system (oxidized and lost as carbon dioxide
to the atmosphere). Therefore, to get the best
out of a no-tillage system, the challenge for
machinery designers is to provide no-tillage
openers that can cope with any amount and
type of surface residue without blockage.
But, more than that, as is explained in
Chapter 5, an opportunity exists for openers
to harness the surface residues as an important
resource to aid germination and emergence
of the new crop.
Large field-scale no-tillage
Weed control and management of
cover-crop residues
In larger field-scale no-tillage, weeds and
cover crops are normally killed by herbicides.
Indeed, the very feasibility of the
modern concept of no-tillage owes its existence
to the development of ‘non-residual’
herbicides in the 1960s and 1970s. This
contrasts with small-scale agriculture (see
below), which is more dependent on mechanical
means of plant competition control.
No attempt is made here to analyse the
pros and cons of specialist spraying
machinery or different herbicides. Suffice
to say that the control of existing competition
is the first step in any no-tillage
programme and that, unless this is achieved
effectively, all other steps will be compromised.
Effective chemical weed control is a
function of understanding the biology of the
plants to be killed and the efficacy of the
herbicide(s) to be used and the mechanical
performance of sprayers. Some herbicides
(e.g. glyphosate) work best on actively growing
unstressed plants, while others (e.g.
paraquat) are more effective when plants
are stressed. And, of course, there are
species differences (and sometimes varietal
differences) in the resistance of plants to
different herbicides.
Management of harvested residues
CHOPPED OR LONG? The first and most
important opportunity to correctly manage
residues on a field scale occurs at harvesting.
Once crops have been threshed and the
residues ejected from a combine harvester
in discrete windrows, they are very difficult
to spread out again.
138 C.J. Baker et al.
Modern combine harvesters gather
together the material from cut widths of
5–10 m and process it in such a way that,
unless spreading devices are added to the
combine harvester discharge, the residues
are ejected out of the back in the form of a
windrow of light fluffy straw 2–3 m wide.
Underlying this windrow will be the chaff
from the separation processes, which consists
of very short pieces of straw, awns, leaf
material, empty glumes, chaff, dust and
weed seeds. The chaff row forms a dense
surface covering, somewhat narrower than
the straw windrow covering it.
In contrast to these somewhat concentrated
zones of residue, good no-tillage
requires that the residue be spread evenly
over the entire field. There are no-tillage
openers that can physically cope with the
concentrated windrows and tailings, but
this capability is somewhat academic since
the effect of surface residues on germination,
emergence and crop growth is so vital
that an uneven crop will almost certainly
result from grossly uneven chaff and straw
distribution. Uneven spreading can also
affect the efficacy of herbicide applications.
Most combine harvesters have optional
straw spreaders. These are different from
straw choppers in that spreaders do not
chop the straw into shorter lengths. They
spread the straw with beaters rather than
with wind assistance (see Fig. 10.3). Most
straw choppers spread as well as chop. Straw
spreaders are not high power-demanding
additions and are easily fitted and operated.
They are essential standard equipment on
all combine harvesters for no-tillage systems,
as indeed they already are on some
makes and models.
Whether or not a chopper is also needed
will depend on the residue-handling
capabilities of the no-tillage drill or planter
to follow. Straw choppers are unpopular in
some respects because they consume up to
20% of the total power requirement of the
combine harvester (Green and Eliason,
1999). Chopping damp straw requires more
power than chopping dry straw, although
the distribution of damp straw on the soil
surface may be more even than that of dry
straw.
Generally, if the straw needs chopping
to avoid the no-tillage openers blocking,
this reflects inadequate performance on the
part of the openers.
CHAFF. Another area of concern is the tailings
or chaff. With some openers, this thick
mat of fine material is more troublesome
than thick straw. Fortunately, in recognition
of this, many combine harvesters now
offer chaff spreaders (or tailings spreaders)
as well as straw choppers or spreaders (see
Fig. 10.2).
Most straw choppers/spreaders can be
adjusted to produce longer or shorter cuts
and to spread the residues different distances
through adjustments of the deflector,
the vertical positions of the knives and
the speed of the chopper (Siqueira and
Casão, 2004).
Some modern straw choppers use
improved cutting principles and blower
support for spreading. For example, auger
types can be applied to both straw and
chaff with spreading widths up to 10 m in
either direction without visible separation
of different fractions (Lücke and von
Hörsten, 2004).
SPREADING AFTER HARVEST. There are limited
residue management options available
where it is not possible to spread
the residue with the combine harvester.
Re-spreading of the residues evenly after
harvest has been only partially successful
because most straw is light and fluffy, making
it difficult to throw or blow any distance.
One way of handling the situation
after harvesting is to pass the material
through a large fan or forage harvester and
blow it as high into the air as possible on a
mildly windy day. In this manner the wind
will spread it reasonably evenly, but it
requires a tractor with cab and good air filtration
system or an operator who can tolerate
dusty conditions. Variations on this
have been attached to combine harvesters
to create ‘straw storms’.
Another way is to use straw harrows,
which consist of feely rotating angled
spikes that are pulled at an angle and flick
the residues more evenly across the field.
Residue Handling 139
They also double as a convenient way to
disturb weeds seeds and induce them to
germinate so they can be killed with a herbicide
before drilling the next crop (referred
to as ‘chitting’ in Europe).
Small-scale no-tillage
The killing of cover crops on a small
scale is not as dominated by herbicides
as is the case for large-scale no-tillage.
140 C.J. Baker et al.
Fig. 10.2. A straw and chaff (tailings) spreader on a combine harvester. Note the dust associated
with spreading chaff.
Fig. 10.3. A pair of simple beater-type straw spreaders on the rear of a combine harvester.
No attempt is made to spread chaff (tailings) with such a device.
Mechanical destruction is frequently used,
or a combination of mechanical and chemical
methods. Mechanical destruction is
favoured because it results in lower repetitive
cash outlays and less exposure by small
farmers and their families to chemicals,
although chemicals such as glyphosate
have a high level of safety associated with
their use. But other herbicides (e.g. paraquat)
are less safe and more difficult for farmers
operating on small fields to take proper
protective measures against than in larger
operations, where fully enclosed vehicle
cabs with filtered air supplies are common.
Mechanical methods for cover-crop handling
in small-scale agriculture are therefore being
widely promoted.
Mechanical destruction of growing
plants is achieved by slashing, chopping,
crushing, spreading or bending the plants.
Each method is suited to different conditions
and results in different amounts of
plant material being left on the soil surface.
Manual slashing
Manual slashing is a very labour-intensive
operation. Schimitz et al. (1991) reported
that labour requirements of 70 man-days/ha
for manual slashing have been measured
when managing a 3-year-old grass-residue
field yielding 10 t/ha dry matter.
Knife roller
Knife rollers are amongst the more useful
residue-management tools to achieve evenly
distributed plant material on the soil surface.
Figures 10.4, 10.5 and 10.6 show examples of
Residue Handling 141
Fig. 10.4. Side view of a knife roller: (1) frame; (2) bearings; (3) transport wheel; (4) protection
structure; (5) shaft (from Araújo, 1993).
Fig. 10.5. Animal-drawn knife rollers: (left) with full-width knives and (right) with short knives.
typical knife rollers. They have the advantage
of allowing non-chemical organic
production methods to be combined with
no-tillage. For example, such implements
are in common use for no-tilled organic
soybeans in southern Brazil (Bernardi and
Lazaretti, 2004) and are available for both
animal and tractor power.
Knife rollers have flat metal knives
mounted on a roller with a frame for support,
wheels for transport and a protective
structure. The knives are mounted on
the roller in various patterns, most commonly
perpendicular to the direction of
travel. The effect of the knives is to bend,
crush and chop off plant material. Their
effectiveness depends upon the width,
diameter and weight of the roller, the
number, height, mounting angle and sharpness
of the knives, speed of operation
and the fibre and moisture content of the
plants (Schimitz et al., 1991; Araújo et al.,
1993).
Rollers are constructed from either
steel or wood. Steel rollers are often filled
with sand, so that their weight can be
adjusted according to the condition of the
plant material and the desired result of
chopping, crushing or bending. But on
slopes the sand can move to one side of
the roller and affect the evenness of performance
and stability. Monegat (1991) recommended
roller widths between 1 and 1.2 m
as a compromise between stability on hillsides
and an ability to stay in contact with
irregular surfaces.
Knives may be the same width as the
roller (Fig. 10.5 – left) or in short sections
(Fig. 10.5 – right). Shorter sections increase
the pressure exerted as each knife impacts
the ground and spreads the impact forces
more evenly, which is important for draught
animals in particular. For a given diameter
of roller, the effectiveness decreases as the
number of the knives increases because the
pressure on each knife is reduced (Schimitz
et al., 1991). For the best cutting action, the
knives should be perpendicular (i.e. not
angled) to the surface of the roller (Siqueira
and Araújo, 1999).
Tables 10.1 and 10.2 show recommendations
for the construction of knife rollers
for draught animals and tractors, respectively
(Araújo, 1993).
142 C.J. Baker et al.
Fig. 10.6. A tractor-pulled knife roller operating in oats.
The design, construction and operation
of knife rollers must also take safety
considerations into account. When working
on slopes, it is advisable to use a fixed
shaft instead of chains, so that the shaft will
work as a brake for the roller. Other considerations
are manoeuvrability, including
reversing (Schimitz et al., 1991), and the
use of protective shields. Figure 10.7 shows
a protective shield, which is important to
both the draught animal and the operator.
The force required to pull a knife roller
in black oats at the milky seed stage (sown
at a density of 100 kg/ha) was measured at
approximately 3430 N (350 kgf) per metre
of width (Araújo, 1993).
Time requirements for handling black
oats with a knife roller are about 3 h/ha for
animal-drawn and 0.9 h/ha for tractorpulled
(Fundação ABC, 1993; Ribeiro et al.,
1993), although Schimitz et al. (1991)
reported requirements as high as 6 days/ha
with animal-drawn units.
The crushing action of knife rollers
interrupts the flow of sap through the plant,
which will kill many annual plants if
the timing is correct (see Fig. 10.8). In this
regard, it is best if the cover crop is uniform
and rolling is undertaken at the beginning
of the reproductive stage, when seeds are
not yet viable. This is at full flowering for
leguminous species and at the milky stage
for cereals (Calegari, 1990). In some environments,
such as sub-Saharan Africa, it is
desirable that the cover crop remains green
as long as possible to avoid burning during
the dry season. In this situation, a knife
roller should be used at the beginning of the
rainy season, prior to planting.
Different methods of cover-crop residue
handling will result in different rates
of biomass decomposition. Araújo and
Rodrigues (2000) compared the decomposition
rates of black oats (Avena strigosa) as a
function of mechanical treatment. They
found that after 68 days the residues
Residue Handling 143
Roller
Diameter
(cm)
Height of
knives (cm)
Number of
Material Density (kgf/m3) knives
Eucalyptus wood 1040 60 5 5
10 6
15 6
Steel + sand 2000 40 10 4
60 5 10
10 10
Table 10.1. Recommendations for the construction of animal-drawn knife rollers
(1 m wide) operating at 1 m/s (3.6 km/h) (from Araújo, 1993).
Roller
Speed,
m/s (km/h)
Diameter
(cm)
Height of
knives (cm)
Number of
Material Density (kgf/m3) knives
Eucalyptus wood 1040 2 (7.2) 40 5 4
10 4
15 6
Steel + sand 1500 2 (7.2) 30 15 12
3 (10.8) 25 8 4
Table 10.2. Recommendations for the construction of tractor-mounted knife rollers (1 m wide)
(from Araújo, 1993).
remaining in relation to the initial amount
were 59% for a knife roller, 48% for a flail
mower and 39% for herbicide application.
A similar study carried out by Gamero et al.
(1997) indicated that after 75 days the
amount of black oat dry matter was 68% for
a knife roller and 48% for a flail mower.
The authors also found a lower weed
144 C.J. Baker et al.
Fig. 10.7. A protective structure for the draught animal and operator alike.
Fig. 10.8. Black oats killed with a knife roller.
population when the knife roller was used
compared with a flail mower.
Yano and Mello (2000) evaluated the
distribution of various cut lengths of pigeon
peas (Cajanus cajan) as a result of different
mechanical treatments of cover-crop residues.
A flail mower resulted in 70% of the
cut lengths being 100 mm or less compared
with 45% for a rotary mower and 22% for a
knife roller.
Another advantage of mechanical treatment
of heavy cover-crop residues is that,
if the crop is sprayed with herbicide
before mechanical treatment, the main
canopy may prevent the herbicide getting to
lower-growing weeds beneath the canopy.
Alternatively, the cover crop can be treated
with a knife roller and then sprayed, provided
that sufficient time is allowed for the
weeds to appear through the bent-over
canopy so that they can be targeted by the
spray. This option is best suited to heavy
cover crops. Spraying options are most
effective where the cover crop is not heavy.
Can a knife roller substitute for herbicides?
Knife rollers are not designed for weed control,
even though the mulch they produce
may contribute to weed suppression. But
one purpose of growing a cover crop is to
pre-suppress the weeds with a dominant
monoculture, which can itself be killed by a
knife roller at the appropriate time prior to
planting the main cash crop. If the cover
crop is vigorous and the weed incidence is
low, a knife roller alone may be sufficient to
prepare the field. In Tanzania, for example,
Schimitz et al. (1991) reported that a knife
roller had been effective for weed control in
grass up to 3 m high after a fallow. The factors
that make such a totally mechanical
option viable are:
1. Perform the planting operation as close
as possible to the destruction of the cover
crop.
2. Use planters with minimal slot disturbance.
3. For planters that create substantial slot
disturbance, plant before the cover crop is
treated so that the residue will cover the
slot opened by the planter.
Management of Residues by
Openers, Drills and Planters:
Micro-management of Crop Residues
Micro-management refers to how the residues
are handled by the openers themselves
and the role the residues play in the opener
functions. It is a sad fact that the designers
of many no-tillage openers still treat
residues as an unwanted nuisance. While
recognizing the macro-value of residues to
no-tillage, these designers often show little
sign of recognizing the micro-value of residues
for opener function and seeding results.
As explained in Chapter 5, the highly
desirable Class IV slot cover is only possible
if the ground is residue-covered in the first
place and then only if the openers are designed
in such a way as to retain that residue
over the slot itself.
Opener handling of residues
Chopping (strip tillage)
All power till openers chop the surface residues
with the soil. There is no practical way
to avoid their doing this. Where the surface
residues consist of undecomposed accumulated
organic matter in colder climates,
such incorporation may be of benefit, but,
in all other circumstances, some of the value
of no-tillage is lost when the residues are
incorporated, even on a strip scale. Besides,
strip tillage itself defeats some of the objectives
of true no-tillage in the planting zone.
Sweeping aside
Hoe, knife, shank, angled flat disc and
angled dished disc openers all push soil
and some of the surface residues aside as
they proceed through the soil. Disc openers
may also push some of the residue into the
soil to form hairpins in the seeding slot.
With hoe- and shank-type openers, if the
residue is reasonably thick and of some
length, it will accumulate on the shank of
the opener rather than be pushed aside,
causing opener blockages. Angled disc-type
openers do not have this problem, but, in
Residue Handling 145
either case, residue that is pushed aside
will have negligible influence on the microenvironment
within the slot that is being
created.
On the other hand, because the residue
is usually heaped to one or both sides of the
slot (Fig. 10.9), careful choice and operation
of a subsequent covering device may succeed
in collecting some of this residue and
guiding it back into the slot zones (Class III
cover), although it is then likely to be mixed
with soil. This process will occur if the soil
remains dry and friable. If the soil becomes
damp, the covering device is likely to create
a smearing effect and the value of the residue
will be lost by becoming smeared into
the soil alongside but not over the slot.
Pushing down or through
All discs, to a greater or lesser extent, push
down through surface residues. Double or
triple disc openers mostly push down,
whereas angled discs sweep aside as well as
push through. The problem with pushing
down is that, because it is impossible to cut
all of the residue all of the time, a proportion
of residue is doubled over and pushed
(tucked) down into the slot in the form of a
‘hairpin’.
The tendencies of different discs to
hairpin depend on several factors:
1. Sharpness of the disc. Sharper discs are
more likely to cut than to hairpin, but it is
impossible to keep discs sharp all of the
time.
2. Brittleness of the straw. Brittle straw
is more likely to break than fibrous straw.
Brittleness itself is a function of crop
species, dampness and stage of decay.
3. Softness of the soil. Firm soil will assist
shearing by a disc (the anvil effect) more
than soft soil. More hairpinning will occur
in soft soils.
4. Speed. Faster operating speeds generally
reduce the incidence of hairpinning.
The straw has less time to bend because of
its inertia and is therefore more likely to be
cut or broken.
5. The presence of chaff and tailings.
Where straw is lying over a mat of fine
tailings, as is often the case, the tailings
provide a soft mat beneath the straw, which
acts like a soft soil and encourages hairpinning.
Worse, a portion of the tailings
themselves may be pushed down into the
slot, where they make the hairpinning problem
worse by coming into contact with the
seed.
146 C.J. Baker et al.
Fig. 10.9. Residue swept to one side of a no-tillage slot.
6. Diameter of the disc. Smaller-diameter
discs, because of their reduced footprint
area, will put more pressure on the residue
than larger discs and are therefore more
likely to cut the residue than to hairpin it.
But small discs are also more likely to
sledge, since larger discs have a flatter cutting
angle at the soil surface.
7. Disc design. Wavy-edged discs, because
of their self-sharpening tendencies, will cut
better than plain discs. Notched discs do
not remain any sharper than plain discs but
cut more residue because of the slicing
action of the sides of the ‘points’ and the
increased footprint pressure of the ‘points’.
Folding up from beneath
The disc version of winged openers manipulates
the surface residues by first pushing
a notched disc down through the residues
and then using the lateral wings of the side
blades to fold the residue and soil upwards
and outwards while the seed and fertilizer
are deposited in the slot. A pair of following
press/gauge wheels then fold the material
back over the seeded slot. The end result is
a horizontal slot covered with soil and
residue (Class IV cover) in much the same
layering as the soil and residues had been
before seeding.
The limited amount of vertical hairpinning
caused by the notched disc is of
little consequence because, unlike with all
other no-tillage openers, the seed is placed
to one side of the central disc slot away from
any hairpins. In this way the seed is effectively
separated from any hairpinned material
and instead benefits from the presence of
residues over the slot (see Chapter 5).
Row cleaners
One method of assisting no-tillage openers
to operate in residues is to clean the row of
residues immediately ahead of the openers.
The devices designed to achieve this
are known as ‘row cleaners’ or ‘residue
managers’.
With small-scale no-tillage, it is often
not feasible to use disc openers because of
the weight required to push them into the
ground compared with tine- or shank-type
openers. ‘Row cleaners’ require little additional
weight since most of them only work
on the surface of the ground. But in such
situations they may make the difference
between being able to undertake no-tillage
or not.
With large-scale no-tillage, where
weight is less of a problem, ‘row cleaners’
are often used in springtime to remove residues
from over the immediate row area so
as to allow sunlight to warm the soil more
quickly after a cold (and often freezing)
winter.
Most ‘row cleaners’ consist of spiked
rotating wheels, notched discs or rakes set
at an angle to the direction of travel and
operating ahead of the openers. The spikes
just touch the ground, which causes them to
rotate much like a finger-wheel rake for
turning hay. In the process, they sweep
the residues to one side or both sides while
at the same time moving as little soil as
possible.
With tougher residues, such as maize
stover, two wheels may be set at opposite
angles to one another and the spikes are
synchronized at their fronts to reduce the
side force on the whole device by sweeping
residues to both sides of the row rather than
to one side. Figure 10.10 shows a ‘row
cleaner’ consisting of a pair of synchronized
spiked wheels. Figure 10.11 shows unsynchronized
notched discs designed to push
residues aside.
Chopping of straw into short lengths
There is a critical length for most straws,
above which they will bend and thus wrap
around approaching rigid tools (e.g. tines).
Chopping all straw into relatively short
lengths allows short lengths to fall away
from rigid tools rather than wrap around
them. Other objectives for chopping straw
trace their origins to tillage by making the
straw easier to incorporate into the soil and
enhancing the decomposition process.
To drill into maize stover with shanktype
openers, Green and Eliason (1999)
Residue Handling 147
recommended that the cut lengths should
be no longer than the shank spacing of the
openers.
Chopped straw may also settle down
on to the ground more easily and closely
than long straw and may therefore provide a
more effective mulch. On the other hand, an
effective no-tillage opener will ensure that
even long straw is replaced on the ground
after its passage (see Fig. 10.1).
One of the most effective ways to obtain
chopped straw is to fit a straw-chopper to
the rear of a combine harvester. Such devices
are not readily favoured by operators,
however, because they consume considerable
power and are yet another component
148 C.J. Baker et al.
Fig. 10.10. A pair of synchronized star wheels (row cleaners) for pushing residues aside.
Fig. 10.11. A pair of angled, notched, disc row cleaners designed to push residues to either side
of the row ahead of the opener.
that must be adjusted correctly on an
already complicated machine. In any case,
they seldom chop every single straw, with
the result that the long straws that persist
may eventually accumulate on openers not
equipped to handle them.
Other methods produce chopped straw
with a separate chopper. Some of these
machines incorporate the straw into the soil
as they chop it, which departs from true
no-tillage because of the general soil disturbance.
Others simply chop it and redistribute
it back on the ground again.
Yet a third approach is ‘vertical mulching’,
where the straw is chopped and then
blown into a vertical slit created simultaneously
in the soil by a large soil opener on
the machine (Hyde et al., 1989; Saxton,
1990). The result is a series of vertical slits
filled with straw, thus solving a disposal
problem as well as providing an entry zone
for water infiltration.
Because no general tillage takes place,
vertical mulching complements no-tillage,
but the absence of a horizontal surface
mulch reduces the options for maximizing
the benefits of true no-tillage. Figure 10.12
shows a prototype vertical mulching
machine in the USA.
Random cutting of straw in place
The most obvious way of handling long surface
residues in place is to cut a pathway
through them with some form of sharp tool.
Generally, discs are the most commonly
used device but other forms of tool have
included rigid knives and powered rotating
blades.
Rigid knives
These have been known to work for short
periods only if their cutting edges remain
smooth and very sharp, but extended use
is impossible because of random damage
and dulling by stones and soil abrasion.
Figure 10.13 shows a knife-edge opener where
the sweeping action of a tapered front was
combined with a sharp edge in an attempt
to slide past and/or cut residues. The sliding
action was unsuccessful because small
imperfections soon developed in the otherwise
smooth edge from contact with stones,
Residue Handling 149
Fig. 10.12. A prototype vertical mulching machine.
resulting in straw catching as it slid down
the face. This led to deterioration of the
cutting effect and blockage.
Rotating blades
These, such as on power till openers, are
not always successful either. To be most
effective as a soil pulverizer, power till
blades are usually L-shaped. The horizontal
portion of the L is important because it elevates
and accelerates the soil upwards and
throws it against the surrounding cowling,
breaking it into smaller particles. Unfortunately,
the horizontal L is also a perfect
catch for wrapping of residue. As a consequence,
backward-facing C-shaped blades
are often used in residue situations because
they allow the residue to be brushed off as
they rotate. C-shaped blades, however, do
not have a truly horizontal portion to the
blade and the trade-off is that they are less
effective as a soil pulverizer.
Discs
These can be most effective for breaking
through or slicing straw, but, as explained
previously, their action is highly dependent
on the firmness of the background soil
against which they must shear the straw and
the brittleness of the straw itself. No matter
what design of disc is used, no disc will cut
all of the residue all of the time.
Cutting damp fibrous straw is particularly
difficult. Cutting it against a soft soil
background is even more so. One variation
that has been tried is to power the disc so
that it rotates faster than its peripheral forward
speed. The aim is to create a slicing
action as the disc presses the residue against
the ground. Figure 10.14 shows a prototype
powered disc. A further variation is to
cause the disc to vibrate as it rotates by
using a power drive on the disc hub. Both of
the powered disc options, however, are disadvantaged
by the cost and complexity of
providing individual drives to a multiplicity
of openers together with the interruption
to residue flow between adjacent
openers brought about by the bulkiness of
such drives in the vicinity of the disc hubs.
Besides, some unpowered designs have
managed to achieve comparable results at a
fraction of the cost.
The most appropriate diameter of discs
for handling agricultural residues is always
a matter for debate. Small-diameter discs
have a smaller footprint and are therefore
easier to push into the soil than larger discs.
For this reason they also cut residues better
than larger discs. However, the closer the
disc axle is to the ground, the easier it is to
stop the disc rotation (stall) when the
150 C.J. Baker et al.
Fig. 10.13. A prototype knife-edge opener designed to sweep and cut residue (from Baker et al., 1979a).
thickness of residue exceeds the height of
the disc axle. Also, a large-diameter disc
has a flatter angle of approach between the
leading edge of the disc and the ground,
making it less likely to push (‘bulldoze’)
the residue ahead of it and more likely to
trap it in the ‘pinch zone’ and then roll over
or cut through it. The most appropriate disc
size is a compromise between getting sufficient
penetration and avoiding disc stall.
The most appropriate disc diameters used
in agriculture seem to be between 450 mm
(18 inches) and 560 mm (22 inches) and are
used extensively on no-tillage openers.
DISC DESIGNS. Another debatable aspect is
the design of the disc. Essentially discs can
be of five designs.
PLAIN FLAT DISCS (FIG. 10.15). These are used on
more no-tillage openers than any other form.
They are the least expensive option to manufacture
and have a sharpened edge, although
experiments have shown that sharpening of
the edge is not altogether necessary in all
situations. They have the least traction of all
alternate designs to ensure turning, which
is not a disadvantage when used in short
standing residue, but can be a disadvantage
in long lying residue. When sharpened, their
action is intended to be one of cutting the
residue, but as the edge becomes dull they
tend to trample rather than cut some of the
residue. As such, they have a strong tendency
to hairpin when configured as double
discs, angled flat discs or a single vertical
pre-disc.
One redeeming feature of flat discs is
that they are able to handle large woody
sticks better than most other discs. The
smooth edge tends to push such sticks
away, whereas other disc types may slice
into and catch on the sticks without actually
cutting them, which then prevents the
disc from rotating.
WAVY-EDGED ‘FLAT’ DISCS (FIG. 10.16). T h e s e
are designed to gain maximum traction by
interrupting the smooth sides of plain discs
with a series of ripples. These ripples are
designed to ‘gear’ the disc to the soil, ensuring
the disc will rotate in even the heaviest
lying residue. For reasons that are not well
understood, the ripples also result in the
discs being self-sharpening. As such, their
action is more one of cutting than with
Residue Handling 151
Fig. 10.14. A powered disc opener designed to rotate faster than the speed of travel through the soil.
plain discs, making them somewhat less
likely to hairpin. Penetration forces are
similar to those of plain flat discs. Although
wavy-edged discs are sharper than plain
discs, making penetration easier, their
waviness actually increases their footprint
area and increases rather than decreases
required penetration forces.
Their self-sharpening tendency also
results in relatively high wear rates. The ripples
also become collection zones for sticky
soils, interrupting their effective functioning.
Their most common use is as a single
pre-disc ahead of rigid components such
as hoe openers. They may also have the
function of loosening the soil ahead of
the double disc openers so as to counter the
compacting tendencies of such discs. They
are sometimes known as ‘turbo-discs’ for this
reason.
NOTCHED, OR SCALLOPED, FLAT DISCS (FIGS 4.27
AND 8.10). These have semicircular notches
cut from their peripheries, leaving about
50% of the periphery as ‘points’ (actually
they are not points, as such, but simply a
portion of the edge of the original plain disc
left unaltered) and 50% as gullets. The
objective is to reduce the footprint area on
the ground, which aids penetration when
compared with plain discs, and to ‘gear’ the
disc to the soil to assist traction. The
‘points’ of the disc penetrate the soil first
and present approximately half the footprint
area of a plain disc of the same diameter,
although the gullet zones of the notches
also eventually penetrate the soil to a
152 C.J. Baker et al.
Fig. 10.15. A plain flat disc.
Fig. 10.16. A wavy-edged ‘flat’ disc.
shallower depth. The net effect, therefore, is
easier penetration than with plain or wavyedged
discs.
Furthermore, as the ‘points’ penetrate
the soil, they change their angle of attack
slightly as they progress further around the
rolling circle. One important effect of this is
that the near-vertical edges from the ‘points’
to the gullets slide into the soil at a range of
angles and thus produce a slicing action
against a portion of the residue. This cuts
that portion of the residue more effectively
than when it is simply pressed on from
above, as with all other disc types.
DISHED, OR CONCAVE, DISCS (SEE FIGS 4.10 AND
4.11). These are nearly always angled to the
direction of travel. As such, the friction
against them is increased compared with
plain discs travelling straight ahead. They
therefore have good traction and are less
likely to stall in heavy, flat residue than
plain discs, but have all of the other attributes
of plain discs, including power requirements
and a tendency to hairpin residue.
One of the difficulties with all angled
discs is delivery of the seed to the U-shaped
slot created behind the lee (back) side of the
disc. Usually, a boot is positioned close to
the disc beneath the ground, but the gap
between this boot and the disc is a collection
point for random residue when used in
no-tillage. Unless this gap is continually
adjusted, blockage soon results.
One way of solving the problem is to
spring-load the boot so that it rubs on the
disc at this point. An advantage of dished
discs is that their curvature provides considerable
strength, allowing the discs to be
made from thinner steel than is common for
flat discs of any nature. This in turn has
clear advantages as far as penetration and
sharpness are concerned. For example, a
3 mm thick disc will require only 60% of
the penetration force required for a 5 mm
disc, although with dished discs this advantage
is offset by the resistance to penetration
of the convex (back) side of the disc.
NOTCHED DISHED DISCS. These combine the
attributes of dished discs with those of
notched discs. Although such designs have
been used extensively in heavy residues for
cultivating new land from native scrub and
felled bush, there are no known no-tillage
openers that use the principle in a more
refined role. Similarly, there are no known
no-tillage openers that use a wavy-edged
dished disc.
Realigning residue on the ground
A novel approach to avoiding hairpinning
with plain discs has been to use realigning
fingers ahead of the discs. One drill of US
origin had vertical spring tines designed to
agitate and jostle the lying straw so as to
cause each straw to lie end-to-end with the
approaching disc. This was intended to
avoid the tendency of discs to pass across
straws, the starting point of all hairpinning.
The tangled nature of many straw residues,
however, ensured that this approach was
never wholly successful.
Flicking
Another novel approach to the operation of
single plain or wavy-edged discs ahead of
rigid tines has been to attempt to flick off
any residue that collects on the leading
faces of the tines, since a single disc operating
ahead of a rigid tine will not allow that
tine to pass cleanly through lying residue
all of the time. Clean-cutting ahead of a tine
can sometimes be achieved with short cut
straw and often with anchored residue, but
long and lying residues are another problem.
Regardless of how well the disc cuts
the residue, there will always be some straw
remaining uncut and passing the disc to
collect on (or wrap around) the tine. Even
when the disc is positioned close to, or even
touching, the front edge of the tine, residue
will collect on this front edge. Besides, it is
most difficult to ensure that a disc remains
permanently touching a tine when both are
subject to normal wear.
Scottish designers created a self-flicking
device (Fig. 10.17). Two spring-loaded fingers
were attached to the hub of the disc in
such a way that, as the disc rotated, the fingers
became tensioned against the ground.
At a certain point in the rotation, each of the
Residue Handling 153
fingers was suddenly released from the
ground, whereupon it flicked upwards at
high speed past the front edge of the tine
and dislodged residue that had collected
there. Similar devices have been used by
the authors, but these were attached to
separate wheels that ran alongside the tine.
While the flicking devices worked in
light and dry residues, heavy residues,
especially when wet, tended to interfere
with the flicking action. Failure to dislodge
all of the straw from the tine with any one
flick became a cumulative problem, leading
eventually to total blockage of the tine.
Treading on residues
To overcome the ‘hit-and-miss’ nature of
flicking, recourse to more predictable treading
has been tried with mixed success. To
achieve this, wheels are located alongside
the tines so that they continuously roll on to
one side of the residues wrapped around the
leading edges of the tines. The intention is to
cause the residue to be pulled off to one side.
Even though they may achieve this objective,
the presence of the wheels themselves
generally interferes with free passage of
other lying residue between the openers.
Self-clearance by free fall of residues
off tines
Provided that sufficient space can be provided
around each tine, most accumulated
residue on the front of tines will eventually
fall off, simply as a function of its own accumulated
weight. Unfortunately, this does
not always occur, especially with wet residue,
necessitating irregular stops to clear
what can become a sizeable mound of accumulated
debris. Not only do these mounds
of debris on the ground interfere with subsequent
operations, their clearing is invariably
a source of annoyance for operators at
seeding time.
The most serious disadvantage of this
principle, however, is the spatial demands
on the drill required for clearance between
individual tines. Drills of this type are limited
to relatively wide row spacing (250 mm
or greater) and the extended area occupied
by the tines interferes with accurate surface
following by individual tines and seed
delivery.
Unfortunately, there are some designers
and operators who are willing to widen
the row spacing of their drills beyond what
is agronomically desirable, expressly to
154 C.J. Baker et al.
Fig. 10.17. A flicking device designed to self-clean stationary tines.
provide more clearance for residue. But, if
anything, no-tillage, by conserving soil
moisture, should allow closer row spacing
to be used than for tilled soils, with resultant
higher potential crop yields. An example
of a drill with wide row spacing is
shown in Fig. 4.15.
Combining rotating and non-rotating
components
An important new residue-handling principle
was designed in 1979 (Baker et al.,
1979b). This involved rubbing the entire
leading edge of a rigid component (such as a
tine, shank or blade) against the vertical
face of a revolving flat disc. For the rubbing
action to be self-adjusting (so as to accommodate
wear of components), the stationary
component needs to be wedge-shaped so
that it presents a sharp leading edge against
the disc but tapers outwards away from the
disc towards the rear. In this way it is held
against the disc by lateral soil forces as the
soil flows past. If two such rubbing components
are positioned one on either side of
the disc, all of the soil forces become symmetrical,
thus avoiding undesirable sideloading
on the discs and their bearings.
The design is illustrated in Figs 4.27
and 8.2. In the design of the disc version of
a winged opener, an opportunity was taken
to deliver the seed to the base of the slot by
directing it to fall between one such stationary
blade and the corresponding face of the
disc. By directing fertilizer in an identical
manner down the other side of the disc, an
effective method of horizontal separation of
seed and fertilizer in the slot was achieved
(see Chapter 9).
There are four important principles
involved in the rubbing action:
1. The intimate contact between the stationary
blades and the revolving disc allows
any residue passing the disc to also pass the
whole assembly, thus making openers
involving a rigid tine or blade at least as
able to handle residues as a pure disc
opener. This combination of disc and rigid
component has achieved a remarkable
residue-handling ability. This is important
because all pure disc openers compromise
at least some of the slot-shape functions to
achieve residue handling. The best microenvironments
for seeds in no-tillage are
generally created by horizontal slots formed
by a rigid tine (see Chapter 4).
2. The contact between the rigid component
and the revolving disc is lubricated by
a thin film of soil (Brown, 1982). This
means that the rigid component can be
manufactured from material that is much
harder (and therefore more wear-resistant)
than the disc, without cutting into the face
of the disc to any appreciable extent.
3. There needs to be a small amount of
pre-load between the rigid component and
the disc, even though, in operation, the soil
continually presses the two together. As the
device enters the soil, and before the soil
forces have pressed the two components
together, a single piece of straw may occasionally
become wedged between the two
components if there is no pre-load between
them. This residue will hold them fractionally
apart for a short period. Other pieces of
straw are then likely to enter the gap, with
the result that blockage eventually occurs.
4. There is a disc-braking effect on the
disc from the rubbing of the rigid components.
For this reason, traction of the disc
must be maximized. Notched flat discs are
most commonly used for this type of
opener, although plain flat discs have also
been used. Wavy-edged discs are unsuitable
because a flat surface is necessary for the
blade and disc contact to be effective.
Wet versus dry straw
The action of most openers is affected by
the brittleness of the straw, which is itself a
function of dampness or dryness as well as
other physical attributes, such as fibre content.
After spraying or physical killing of
growing material, the residue will lose
water and become increasingly ‘stringy’.
Sometimes best results will come from
waiting 10–15 days so that the residues will
dry completely and be more easily cut by
discs. This also allows root material to
begin decaying, which makes the soil more
Residue Handling 155
crumbly and usually leads to better slot formation.
In other situations, drilling might
be undertaken before or immediately after
the residues are killed, provided that competition
for soil water does not take place
between the crop and the cover crop before
the latter is killed.
On the other hand, harvested straw will
normally be at its most brittle shortly after
harvest. Discs are most effective when operating
on brittle straw in warm dry weather and
when the background soil is firm. Standing
residue often becomes increasingly brittle as
it ‘ages’ over winter, making spring no-tillage
seeding more easily accomplished.
The case for and against scrapers
A natural reaction to problems of accumulation
of sticky soil and/or residues on rotating
components of openers is to strategically
place scrapers and deflectors to remove the
unwanted material. Such scrapers and
deflectors can range from those designed
to deflect residue from ever coming near
the opener (e.g. Fig. 10.18) to those designed
to protect a specific part of the opener. Figure
10.19 shows a circular scraper designed
in Canada to remove soil from the inside of
double disc openers.
However, most scrapers create more
problems than they solve. Often, they simply
present yet another point on which
unwanted material can accumulate. While
they may remove the original problem from
interfering with a critical part of the opener,
they seldom result in a total cure from accumulated
debris. With the disc version of
winged openers, both the side blades and
the disc-cleaning scrapers (Fig. 10.20) operate
beneath the ground and are therefore
self-cleaning.
Clearance between openers
Even if individual openers are designed to
freely handle surface residues without
blockage, arranging multiples of such openers
to handle residues in narrow rows is
often a difficult problem in its own right.
The main principles generally involve lateral
spacing. To provide sufficient lateral
space between adjacent openers for residues
to pass through, the openers need to
have a minimum of 250 mm clearance.
Even then, the actions of different openers
156 C.J. Baker et al.
Fig. 10.18. Residue deflectors on a maize planter.
may interfere with their neighbours and
therefore require greater clearance.
For example, while 250 mm might be
sufficient for openers that create minimal
disturbance of the soil (e.g. double disc),
greater distances may be required for those
that either throw the soil (e.g. angled flat
discs and angled dished discs), push it
aside (hoe) or fold it back (winged). In such
circumstances, each alternate opener needs
at least to be offset forwards or rearwards of
its neighbours so as to give diagonal as well
as lateral clearance (referred to as staggering).
An alternative to staggering is to
create greater lateral distances between
openers, but this usually means increasing
row spacing, which may be agronomically
undesirable.
The problem is further complicated by
the greater downforces required for opener
penetration under no-tillage, which is usually
applied to the drag arm connecting the
opener to the drill frame. The strength
required of drag arms to transmit these large
downforces discourages the use of alternately
long and short drag arms to create
staggering, especially if such drag arms are
also of the parallelogram type with multiple
pivots. In contrast, long and short drag
arms are common on drills designed for
tilled soils because the forces are small in
comparison.
One way of overcoming this problem
has been to operate the openers from two
separate tool bars, one in front of the other.
Residue Handling 157
Fig. 10.19. Circular scrapers for double disc
openers.
Fig. 10.20. Underground scrapers on the disc version of a winged no-tillage opener.
This allows the openers on each tool bar to
be spaced twice the distance apart as the
row spacing. If used, it also allows the
longer drag arms for a stagger arrangement
to be of robust construction without interfering
unduly with the between-opener
spacing.
The problem of lateral spacing largely
applies to drills and not to planters, because
drills may have row spacing as close as
75 mm, while planters seldom require row
spacing closer than 375 mm.
Summary of Residue Handling
1. The most serious physical problem
relating to the handling of surface residues
is mechanical blockage.
2. The most serious biological problem
relating to the handling of surface residues
is hairpinning (or tucking) of residues into
the seed slot.
3. Macro (whole field)-management of
surface residues starts with the combine harvester
and is important for soil and resource
management of no-tillage in general.
4. Macro-management should aim at even
spreading of both straw and tailings over the
entire field. Chopping of straw is optional.
5. Micro-management of surface residues
is a function of no-tillage openers and
is important for controlling the microenvironment
of the seed slots.
6. Micro-management should strive to
return the residue over, but not into, the
seed slot (Class IV cover).
7. Large-scale no-tillage almost invariably
involves the use of herbicides to kill existing
vegetation.
8. Small-scale no-tillage relies predominantly
on mechanical or manual residue
management.
9. Knife rollers are a useful tool for management
of residues in small-scale no-tillage.
10. Residue can be classified as ‘short
root-anchored’; ‘tall root-anchored’; ‘short
flat’; or ‘long flat’.
11. ‘Long flat’ residue is the most difficult
to handle.
12. Relying solely on the cutting of residues
is seldom effective. No device will cut
all of the residue all of the time.
13. Most pure disc-type openers handle
residues well, but also tend to hairpin
(or tuck) straw into the slot, which is undesirable.
14. Most rigid component openers (hoe- or
shank-type) handle residues poorly with
regard to blockage but do not hairpin.
15. Most power till openers handle residues
poorly except when the blades are
C-shaped.
16. Wavy-edged and notched discs handle
residues better than plain discs.
17. Small-diameter discs penetrate soil and
residues more easily than larger discs, but
are more likely to form blockages in heavy
residues.
18. Firm soils provide a better medium for
residue handling and cutting by openers
than soft soils, thus reducing hairpinning.
19. Small no-tillage machines often have
poor performance by having tined openers
(due to cost) but benefit from the manual
attention that can be given to residue management
by operators.
20. Wet soil and/or wet residue are more
difficult to handle than dry soil and/or dry
residue.
21. Unless operating beneath the ground,
most scrapers are of limited value because
they accumulate residue on themselves
while they are removing it from elsewhere.
22. Vertical mulching consists of disposing
of straw into deep vertical slits in the soil.
23. Any rigid opener component, such as a
tine or shank, will accumulate residue
regardless of the design or positioning of a
disc ahead of it.
24. Only when the leading edge of a rigid
tine is forced to rub in intimate contact with
the side face of a revolving flat disc will a
tine/disc combination handle residues as
well as a disc alone.
25. The minimum distance between adjacent
openers for self-clearance of residues is
approximately 250 mm, either laterally or
diagonally, or both.
158 C.J. Baker et al.
11 Comparing Surface Disturbance and
Low-disturbance Disc Openers
C. John Baker
The surface disturbance of soil and residues
often represents the most visible difference
between no-tillage openers; yet the real effects
may lie underground.
The passage of a seeding drill over a
no-tilled field causes a wide variety of soil
and residue disturbances, largely depending
on the opener design, soil condition and
operation speed. These disturbances are
quite visible and yet the impacts on crop
establishment and subsequent yields may
only become obvious in stress conditions.
In the first part of this chapter, we
revisit the seeding principles of the previous
chapters to relate the disturbance effects to
the effectiveness of common no-tillage slot
shapes. In the second part, we compare the
design features of common disc-type openers,
since it is mainly disc openers that create
minimum-disturbance slots.
Minimum versus Maximum Slot
Disturbance – How Much Disturbance
Is Too Much?
The largest concern centres on openers that
create significantly different amounts of disturbance,
such as a single, straight-running
disc versus a broad hoe or chisel opener.
These results are recognized as minimum
versus maximum opener disturbance drills.
Minimum disturbance creates just enough
soil mo