Advances in agronomy volume 33

ADVANCES IN

AGRONOMY

VOLUME 33


CONTRIBUTORS TO THIS VOLUME
R. W. ARNOLD
F. H. BEINROTH
R. J . BURESH
F. B . CADY
M. E. CASSELMAN
MARLING . CLINE
G . D. FARQUHAR

R. J . HAYNES
ERNESTA. KIRKBY
T. M. MCCALLA
KONRADMENGEL
W. H. PATRICK,JR.
J . A . SILVA

H . T. STALKER
G. UEHARA

P. W. UNGER
P. D. WALTON
R. WETSELAAR

ADVANCES IN

AGRONOMY
Prepared in cooperation with the
AMERICAN
SOCIETY
OF AGRONOMY

VOLUME 33
Edited by N. C . BRADY
International Rice Research Institute
Manila, Philippines

ADVISORY BOARD
H. J . GORZ,CHAIRMAN
R.B. GROSSMAN T. M. STARLING
I . B. POWELL

J . W . BIGGAR

M. A. TABATABAI
M. STELLY,
EX

OFFICIO,

ASA Headquarters
1980

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CONTENTS
CONTIUBUTORS
TO VOLUME
33 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
PREFACE
.....................................................

ix
xi

CONSERVATION TILLAGE SYSTEMS

P. W. Unger and T . M . McCalla
I . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
I1 . Historical . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
III . Tillage Equipment and Use ...............................
IV . Crop Yields and Quality .................................
V . Environmental Consideration .............................
VI . Infiltration and Water Conservation ........................
VII . Weed Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
VIII . Insects and Plant Diseases ................................
IX . Soil Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
X . Soil Structure and Other Physical Properties . . . . . . . . . . . . . . . . .

XI . Chemical Effects and Microbial Activity ....................
XI1. Economics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
XI11. Summary and Conclusions ...............................
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2
5
6
13
16
30
35
38
39
43
48
49
51
53

POTASSIUM IN CROP PRODUCTION

Konrad Mengel and Ernest A . Kirkby

I.
I1.
111.
IV .
V.

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Potassium Availability in the Soil ..........................
Potassium in Physiology .................................
Potassium Application and Crop Growth ....................
Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
References ............................................

59
60
74
91
103
103

UTILIZATION OF WILD SPECIES FOR CROP IMPROVEMENT

H . T . Stalker
I . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
I1. Biosystematics .........................................
V

112
113


vi

CONTENTS

111. The Gap between Hybridization and Utilization . . . . . . . . . . . . . .

IV . Approaches for Utilizing Wild Germplasm Resources . . . . . . . . .
V . Examples of Species Used in Wild Species Hybridization
Programs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
VI . Specific Uses of Wild Species for Crop Improvement . . . . . . . . .
VII . Summary and Conclusions ...............................
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

118
119
126
135
140
141

NITROGEN FIXATION IN FLOODED SOIL SYSTEMS. A REVIEW

R . J . Buresh. M . E . Casselman. and W . H . Patrick. Jr .
I . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
I1. Nitrogen Fixation in the Water Column and on the Soil Surface
111. Nitrogen Fixation in the Aerobic Layer of Flooded Soil . . . . . . .
IV . Nitrogen Fixation in the Anaerobic Layer of Flooded Soil . . . . .
V . Nitrogen Fixation in the Root Zone of Nonnodulated Plants . . . .
VI . Nitrogen Fixation on the Leaf and Stem Surface of Plants . . . . .
VII . Environmental Factors Influencing Nitrogen Fixation in
Flooded Soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
VIII . Comparison of Acetylene Reduction and 15N Methodology . . . .
IX * Contribution of Fixed Nitrogen to the Nitrogen Requirements
of Plants ............................................
X . Perspectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

150
152
160
161
163
170
174
180
183
185
187

EXPERIENCE WITH SOIL TAXONOMY OF THE UNITED STATES

Marlin G . Cline
I . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
I1 . General Reactions to the System ..........................
111. Use of Soil Taxonomy Internationally ......................
IV . Problems for Users of Soil Taxonomy ......................
V . Taxonomic Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
VI . Impact of Soil Taxonomy Internationally ....................
VII . Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

193
195
197
202
207

213
222
223


vii

CONTENTS
COMPETITIVE ASPECTS OF THE GRASS-LEGUME ASSOCIATION

R . J . Haynes

I . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
I1. Competition in the Pasture Community .....................
111. Physiological Considerations ..............................
IV . Morphological Considerations .............................
V . Competition for Environmental Factors .....................
VI . Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

227
229
231
239
248
254
256

NITROGEN LOSSES FROM TOPS OF PLANTS

R . Wetselaar and G . D . Farquhar
I . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

263
264
111. Possible Pathways of Nitrogen Losses from Tops . . . . . . . . . . . . . 279
IV . Associated Methodology Problems .........................
293
V . Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
298
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
299

I1 . Record of Observed Decreases of Nitrogen Content of Plant Tops

AGROTECHNOLOGY TRANSFER IN THE TROPICS BASED ON SOIL TAXONOMY

F . H . Beinroth. G . Uehara. J . A . Silva. R . W . Arnold. and F . B . Cady

I . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

304
304
Soil Classification in Perspective ..........................
309
Agrotechnology Transference Research .....................
316
Quantitative Verification of Transferability within a Soil Family . 323
Prerequisites for Worldwide Agrotechnology Transfer . . . . . . . . . 332
Conclusion: Implication for Agricultural Development . . . . . . . . . 336

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
338

I1 . The Transfer of Agrotechnology ...........................
111.

IV .
V.
VI .
VII .

THE PRODUCTION CHARACTERISTICS OF Bromus inerrnis LEYSS AND THEIR
INHERITANCE

P . D . Walton

I . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
I1. The Nature of the Species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

341
343


viii

CONTENTS

III . Seed Production and Establishment ........................
IV . Forage Quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
V . Forage Yield . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

VI . Plant Breeding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

347
350
353
363
367

INDEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

371


CONTRIBUTORS
Numbers in parentheses indicate the pages on which the authors’ contributions begin.

R. W. ARNOLD (303), Department of Agronomy, New York State College of
Agriculture and Life Sciences, Cornell University, lthaca, New York 14853
F. H. BEINROTH (303), Department of Agronomy and Soils, College of Agricultural Sciences, University of Puerto Rico, Mayaguez, Puerto Rico 00708
R. J . BURESH* (149), Laboratory for Wetland Soils and Sediments, Center for
Wetland Resources, Louisiana State University, Baton Rouge, Louisiana
70803
F. B. CADY (303), Biometrics Unit, Department of Plant Breeding and
Biometry, New York State College of Agriculture and Life Sciences, Cornell
University, lthaca, New York 14853
M. E. CASSELMAN (149), Laboratory for Wetland Soils and Sediments,
Center for Wetland Resources, Louisiana State University, Baton Rouge,
Louisiana 70803
MARLIN G . CLINE ( 1 93), Department of Agronomy, Cornell University,

lthaca, New York 14853
G. D. FARQUHAR (263), Department of Environmental Biology, Research
School of Biological Sciences, Australian National University, P.O. Box 47.5,
Canberra City, Australia 2601
R . J . HAYNES (227), Department of Soil Science, Lincoln College, Canterbury, New Zealand
ERNEST A. KIRKBY (59), Department of Plant Sciences, The University,
Leeds LS2 9JT, England
T. M. MCCALLA ( l ) , Agricultural Research, Science and Education Administration, USDA, University of Nebraska, Lincoln, Nebraska 68583
KONRAD MENGEL (59), Institute of Plant Nutrition, Justus Liebig University,
0-6300 Giessen, Federal Republic of Germany
W. H. PATRICK, JR. (149), Laboratory for Wetland Soils and Sediments,
Center for Wetland Resources, Louisiana State University, Baton Rouge,
Louisiana 70803
J . A. SILVA (303), Department of Agronomy and Soil Science, College of
Tropical Agriculture and Human Resources, University of Hawaii, Honolulu,
Hawaii 96822
H . T. STALKER ( 1 1 l), Department of Crop Science, North Carolina State
University, Raleigh, North Carolina 27650
*Resent address: International Fertilizer Development Center, P.O. Box 2040, Muscle Shoals,
Alabama 35660.
iX


X

CONTRIBUTORS

G . UEHARA (303), Department of Agronomy and Soil Science, College of
Tropical Agriculture and Human Resources, University of Hawaii, Honolulu,
Hawaii 96822

P . W. UNGER ( l ) , Conservation and Production Laboratory, Agricultural Research, Science and Education Administration, USDA, Bushland, Texas
79012
P. D. WALTON (341), Department of Plant Science, The University of Alberta,
Edmonton, Alberta T6G 2E3, Canada
R. WETSELAAR (263), Division of Land Use Research, Commonwealth Scientific and Industrial Research Organization, P.O. Box 1666, Canberra City,
Australia 2601


PREFACE
The orderly classification of soils in the field is essential to effective utilization
of much production-oriented soil and crop research. Unfortunately, however,
there is all too little exchange of information among scientists concerned with
soil classification. Many soil classification schemes are sufficiently complicated
as to make them not easily understood by most agronomists. This has become
increasingly evident with the development in recent years of comprehensive
international soil classification schemes.
Two of the articles in this volume relate to the classification of soils and to the
usefulness to agronomists of classification schemes. Cline reviews agronomists’
experiences with the most comprehensive of the international classification systems, that developed under the leadership of the U.S. Department of Agriculture.
The views presented are not only those of other pedologists, but also those of
production-oriented scientists and others who have used the new comprehensive
soil classification scheme. Beinroth and coauthors relate the findings of soil and
crop scientists who have compared the performance of soils that have similar
characteristics but are located in different parts of the world. This information is
useful in ascertaining the value of soil survey in agrotechnology transfer.
Nitrogen continues to be a prominent subject for agronomic research. The
fixation of nitrogen in flooded systems is reviewed by Buresh, Casselman, and
Patrick. They emphasize the uniqueness of flooded systems in relation both to
redox potential and to nitrogen-fixing organisms. High nitrogen losses directly
from plants as they mature may account for much of the low rate of utilization of

applied nitrogen. Wetselaar and Farquharreview this subject in their contribution.
Potassium in crop production has received prominent research attention in
recent years, especially in relation to methods of predicting response to this
important element. Mengel and Kirkby provide an excellent review of research on
potassium availability in the soil and the function of potassium in the plant.
The most significant recent change in soil and crop management in the United
States has been in tillage and crop residue management. Over wide areas, tillage
systems that keep most of the crop residues on or near the soil surface have
replaced conventional systems that focused on the moldboard plow. A comprehensive review of the effects of some of these new tillage systems is presented
in the article by Unger and McCalla.
In recent years, scientists have become increasingly successful in implementing crosses between cultivated plants and wild species. These crosses provide
considerable potential to incorporate into cultivated plants such desired characteristics as disease and insect pest resistance and tolerance of drought. Stalker
reviews research on this subject.
Research related to the production of forage crops is the focus of two of the
xi


xii

PREFACE

manuscripts in this volume. Haynes reviews competitive aspects of grass-legume
associations and illustrates how this competition accounts for the dominance of
either grasses or legumes, depending on the ecological stresses. The characteristics of Bromus inermis Leyss that control its production and inheritance are the
subjects of the review by Walton.
The authors of the contributions presented in this volume are from six different
countries. We express sincere appreciation to them for their efforts.
N. C . BRADY

ADVANCES IN

AGRONOMY

VOLUME 33


This Page Intentionally Left Blank


ADVANCES IN AGRONOMY, VOL. 33

CONSERVATION TlLLAGE SYSTEMS
P. W. Unger2 and T. M. McCalla3
Agricultural Research, Science and EducationAdministration,U.S. Departmentof Agriculture

I. Introduction . . . . . . , . . . . . . . . . . . . . . . . . .
...............................
A. Definition of Conservation Tillage Syst
...............................
B. Development and Use of Practices in the United States
....
C. Purpose of Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11. Historical . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
111. Tillage Equipment and Use
.........................................
A. Machinery Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
B. Seedbed Preparation and Crop Seeding . . . .
IV. Crop Yields and Quality . . . . . . . . . . . . . . . . . . .
A. Grain Yields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

B. Plant Protein Content and Mineral Composition . . . . . . . . . . . . . . . . . . . . . . . . . . . .
C. Residue Yields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
D. Root Growth
V. Environmental Consideration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
A. Control of Wind Erosion . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
B. Control of Water Erosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
C. Runoff Water Quality . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
VI. Infiltration and Water Conservation
..........
A. Runoff and Infiltration.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
B. Evaporation
....................
VII. Weed Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
A. Problem Areas . . . . . . . . . . . . . . . . . . . . . . . . . . . .
B. Control with Tillage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
C. Control with Herbicides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
D. Control with Rotations
.......................................
VIII. Insects and Plant Diseases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
B. Plant Diseases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
IX. Soil Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
B. Residue Factors Involved . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
C. Biological Effects of Residue . .

2
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5
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6
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13
14
15
16
16
17
21
29
30
30
33
35
35
36
37
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40
42

'Contribution from Agricultural Research, Science and Education Administration, U.S. Department of Agriculture, in cooperation with the Texas and Nebraska Agricultural Experiment Stations.
zSoil Scientist, Conservation and Production Research Laboratory, Bushland, Texas.

3Microbiologist, University of Nebraska, Lincoln, Nebraska.
1
ISBN 0-12-W733-9


2

P. W . UNGER AND T. M. McCALLA

X. Soil Structure and Other Physical Properties ..................................
........
A. Aggregation ..........
B. Porosity and Density ..................................................
C. Other Physical Properties . .
.................
XI. Chemical Effects and Microbial
XII. Economics . . . . . . . . . . . . . .
XIII. Summary and Conclusions ................................................
A. Accomplishments
.....
.....
B . Needs ..............................................................
References . . .
.................................................

43
44
46
46

51
51
52
53

1. INTRODUCTION
A. DEFINITION
OF CONSERVATION
TILLAGE
SYSTEMS

Conservation tillage systems, as used in this review, are systems of managing
crop residue on the soil surface with minimum or no tillage. The systems are
frequently referred to as stubble mulching, ecofallow, limited tillage, reduced
tillage, minimum tillage, no-tillage, and direct drill. The goal of these systems of
plant residue management is threefold: to leave enough plant residue on the soil
surface at all times for water and wind erosion control, to reduce energy use, and
to conserve soil and water. These systems are used throughout the United States
and the world, and can be applied to all kinds of crop residue in many cropping
systems.
B. DEVELOPMENT
A N D USE OF PRACTICES
IN THE UNITEDSTATES

Stubble mulching was developed as a result of severe wind erosion in the Great
Plains of the United States and Canada during the 1930s. Anchored surface
residue kept the soil in place despite the erratic climate of the Great Plains. Crop
residue on the soil surface was soon found to be equally effective for controlling
water erosion.
A surface mulch of plant residue protects the soil against the beating action of

raindrops and keeps the surface of the soil open, thus increasing infiltration over
that of a bare soil. When enough residue is present, more water is conserved with
a mulch system than with the moldboard plow system. Since the 1930s and
1940s, many effective herbicides have come on the market, which reduced the
need for tillage to control weeds.
Even though the use of crop residue on the soil surface has much merit in
controlling soil erosion and conserving water, use of residue by farmers depends
in the final analysis upon the effects of surface residue on crop yields. Crop
yields are often reduced where plant residue is maintained on the soil surface,


3

CONSERVATION TILLAGE SYSTEMS

particularly on heavier textured soils in the more humid and northern areas of the
United States. This apparently is due to factors such as ( 1 ) lack of proper equipment and knowledge of how to manage the residue with the equipment; (2)
colder, wetter, and less aerated soil; (3) weed, insect, and disease problems; (4)
lower nutrient availability, such as lower nitrate production; and ( 5 ) changes in
the microbial status of the soil and the possible production of phytotoxic substances. In many areas, however, crop yields are often increased by plant residue
left on the surface. In addition, residue use may keep a crop from being lost by
wind erosion.
Despite the lower yields and other problems sometimes encountered with the
use of crop residue on the soil surface, these systems are useful to U.S. farmers.
Demands for improved water quality of the nation’s streams and groundwater
have also stimulated the use of crop residue on the soil surface. At present, over
28 million hectares (over 70 million acres) of land are cropped by minimum or
no-tillage methods (Table I). Limited tillage, especially sod planting, is one
method used in many parts of the United States.
In some instances, the use of crop residue on the soil surface alone is not

Table I
1978 /1979 No-Till Fanner Survey”
No-tillageb
State
Alabama
Alaska
Arizona
Arkansas
California
Colorado
Connecticut
Delaware
Florida
Georgia
Hawaii
Idaho
Illinois
Indiana
Iowa
Kansas
Kentucky
Louisiana
Maine
Maryland
Massachusetts‘

Minimum tillage*

1978

I979

66,170
2,670
410
2,020
490
29,340
7,640
8 1,750
1,620
210,320
233,290
139,980
86,600
393,360
8 10

68,110
2,750
870

1.900

96,830
1,340

1978

50

2,140
490
32,120
1 1,530
108,050
2,830
215,300
259,000
146,090
95,100
470,250
810
2.060
112,490
1,380

83,930
1,850
120,190
109,210
390,570
832,980
770
123,030
48,260
8 17,480
1,093,080
2,040,470
698,250

3,001,360
3,862,810
800,650
236,540
158,570
4,330

1979
78,430
2,250
114,930
124.6 I0
410,700
866,370
1,210
133,310
54,230
997,570
1,097,940
2,246,050
696,070
3,338,730
4,091,460
849,980
238,570
182,790
4,130

Conventional tillageb
1978

1,473,130
3,840
425,740
2,715,170
1,603,680
1,571,230
19,790
55,940
490,810
806,560
113,560
1,333,470
6,433,210
3,155,870
5,665,720
4,634,970
410,280
1,458,720
71,310
226,840
18,490

1979
1,510,680
3,840
432,620
2,699,340
1,673,270
1,537,840
18,540

52,210
505,580
728,450
116,960
1,327,400
6,324,560
3,237,560
5,463,380
4,164,310
416,430
1,548,560
76,160
230,230
18,490
(continued)


4

P. W. UNGER AND T. M. McCALLA

Table I (continued)
No-tillageb
State
Michigan
Minnesota
Mississippi
Missouri
Montana‘
Nebraska

Nevada
New Hampshire
New Jersey
New Mexico
New York
North Carolina
North Dakota
Ohio
Oklahoma
Oregon
Pennsylvania
Puerto Rico
Rhode Island
South Carolina
South Dakota
Tennessee
Texas
Utah
Vermont
Virginia
Washington
West Virginia
Wisconsin
Wyoming
Totals

1978

1979

19,750
47,630
29,950
98,580
8,090
234,320
28,640
400
17,400
2,550
13,150
147,310
3,440
289,360
2,350
12,110
176,040
950
30
8,390
72,240
74,340
59,300
2,430
127,280
3,170
15,580
39,460
-

I 8,050
54,230
35,920
109,470
8,170
225,410
28.940
810
23,470
3,560
13,150
149,330
4,650
297,450
3,160
10,440
176,850
730
30
8,980
62,320
81,950
49,450
2,430
127,840
7,420
17,400
39,660
-

2,890,790 3,092,730

Minimum tillageb
1978

I979

428,980
1,848,640
131,530
1,474,960
263,050
2,613,920
38,360
2,140
8,090
78,310
263,050
255,970
1,297,860
40,470
235,610
127,770
69,130
110

728,250
1,398,220
220,960
607.600

79,930
1,010
157,710
234,690
1,210
359,570
1,210

437,070
1,893,970
148,120
1,445,890
264,470
2,577,090
39,290
2,140
16,190
90,450
265,070
258,800
1,421,690
40,470
239,580
129,830
62,160
I10
734,720
1,643,060
23 1,080
508,040

77,900
1,210
169,970
39 1,460
2,020
361,390
1,210

Conventional tillage*
1978
1,547,470
5,709,230
2,215,900
2,580,760
2,023,470
3,532,580
63,310
9.960
172,800
368,470
443,550
1,391,830
9,531,570
3,914,610
3,681.9 10
576,760
864,020
193,540
2,110
740,150

3,567,990
1,161,390
8.8 17,690
4 15,620
3 11,610
404,530
1,543,830
26,710
1,920,030
220,560

1979
1,541,080
5,679,890
2,199,620
3,831,550
2,058,880
3,146,900
63,770
10,560
157,430
360,180
441,520
1,375,800
9,409,360
3,906,520
3,678,070
566,070
897,610
173,080

2,110
753,540
3,268,310
1,197,090
7,868,000
428,170
31 1,210
402.470
1,382,810
22,260
1,943,100
273,570

27,392,940 28,983,820 90,962,280 89,374,030

“The source of information is the State Agronomists of the Soil Conservation Service. Values
have been converted to hectares. Published with permission from No-Till Farmer, Inc. 61 I East
Wells Street, Milwaukee, Wisconsin 53202.
*Definitions of each of the tillage systems are as follows:
No-tillage: Only the intermediate seed zone is prepared. Up to 25% of surface areacould be worked.
Includes no-till, till-plant, chisel-plant, rotary strip tillage, and many other forms of conservation
tillage and mulch tillage.
Minimum tillage: Limited tillage, but the total field surface is still worked by tillage equipment.
Conventional tillage: Where 100% of the topsoil is mixed or inverted by plowing, power tiller,
or multiple diskings.
‘Estimates provided by Cooperative Extension Service Agronomists.


CONSERVATION TILLAGE SYSTEMS

5

enough for good soil conservation. In such cases, use of residue in combination
with other proven mechanical and conservation cropping practices, such as terracing and contouring, is necessary for more effective soil and water conservation.
C. PURFOSEOF REVIEW

McCalla and Army (1961) reviewed the use of crop residue on the soil surface,
which at that time was called stubble mulching. Because of research since then
and because new equipment and herbicides are available, an inventory of the
available information developed since then was needed, along with an appraisal
of the merits and faults of managing crop residue on the soil surface for control of
water and wind erosion, conservation of water, production of crops, and conservation of energy.
Although the use of crop residue on the soil surface has been widely researched, information is still scarce on many aspects of the system’s influence on
the physical, chemical, and biological soil environment; on insect, disease, and
weed control; on water conservation; and on crop production. Not enough information is available for full implementation of the system across the United States
for various soils, climatic conditions, and crops. Improvements are needed in
equipment for seeding and applying herbicides. Crop varieties developed specifically for residue management systems are badly needed. Also, the economics of
systems involving crop residue need to be fully evaluated.
This review is, in general, limited to the salient points that have been researched since 1961. We have not attempted to summarize all the literature
pertaining to the use of crop residue on the soil surface. Since 1961, numerous
papers have been published, and a number of symposia and reviews have been
made concerning the use of crop residue on the surface. Some examples of the
latter are American Society of Agronomy (1978), Soil Conservation Society of
America ( 1973, 1977, 1979), Great Plains Agricultural Council ( 1962, 1968,
1976), Ohio State University (1972), Plant Protection Limited (1973, 1975), and
USDA (1977). Only pertinent and illustrative data are used to describe the areas
of application and merits and faults of crop residue on the soil surface. Where
essential technical information is lacking, we have called the deficiency to the
reader’s attention.

II. HISTORICAL
The early work was reviewed by McCalla and Army (1961) and Jacks et al.
(1953, and also in a number of the symposia and reviews cited earlier.


6

P. W. UNGER AND T.M. McCALLA

Mulches, to some degree, have been used in agriculture since man first began
to cultivate crops. Orchards and garden crops were probably the first to be
mulched, and mulches usually were several centimeters thick. The Chinese,
many hundreds of years ago, used stone mulches in their agriculture. Also, most
primitive agriculture allowed residue to remain on the surface because the simple
tools, in most cases, did not cover the plant residue.
Crop residue is commonly used as mulches; but paper, plastics, glass wool,
cloth, metal foil, sugarcane trash, manures, leaves, peat, litter, stones, and dust
mulches have also been used. Natural mulches are snow and volcanic dust. Snow
mulch is valuable in protecting a crop such as wheat against winterkill. Snow
also is a major source of water for crop production in many cold regions.
Dr. F. L. Duley and Professor J. C. Russel conducted the first intensive
research in the United States on the use of a mulch for crops. The work was
started at Lincoln, Nebraska, in 1937 by the Nebraska Agricultural Experiment
Station in cooperation with the Research Division of the Soil Conservation Service, U.S. Department of Agriculture. Since that time, these and many other
researchers have studied the management of crop residue on the soil surface. This
research has resulted in the development of the crop residue management systems
that are now known as conservation tillage systems.

Ill. TILLAGE EQUIPMENT AND USE
A . MACHINERY

REQUIREMENTS

Regardless of cropping system, a complement of machinery is needed to
prepare satisfactorily a seedbed, plant seeds, and control weeds and volunteer
crop plants. Because conservation tillage systems rely heavily on surface residue
for erosion control and water conservation, it is imperative that the machinery be
capable of operating satisfactorily when large amounts of residue are on the soil
surface and that most residue be kept on the surface.
Tillage systems developed within the last half century are capable of retaining
most crop residue on the soil surface. These systems are the stubble mulch
system, developed in the late 1930s and early 1940s, and the reduced- or notillage systems, which are essentially still under development.
1 . Stubble Mulch Tillage

Stubble mulch farming is a year-round system of managing plant residue.
Stubble mulch tillage is performed with implements that undercut residue, loosen
soil, and kill weeds. Because the soil is tilled as often as necessary to control
weeds during the period between crops, the stubble mulch system is a tillage-


7

CONSERVATION TILLAGE SYSTEMS

intensive system that requires frequent operations to control weeds. The system
was developed primarily for wheat (Triticum aestivum L.) and other small grain
crops, but is also adaptable to such crops as sorghum (Sorghum sp.).
Good management of a stubble mulch farming system begins with harvest. To
minimize tillage problems, crop residue should be spread uniformly by the combine. In the Great Plains, sweeps or blades are generally operated at the 12- to
15-cm depth during the first operation after harvest and shallower during subsequent operations. Weed control generally is best when the soil is dry at the time
of tillage. In the dry-farming areas of the Pacific Northwest and at more humid

locations where straw production by small grain is usually higher than in the
Great Plains, the first operation is similar to that in the Great Plains, but the
second operation may be deeper than the first to avoid serious plugging of the
equipment by the residue.
When unusually large amounts of residue are present, a disk-type implement
may be used for the first operation to incorporate some of the residue with soil.
This hastens decomposition, but still keeps enough residue on the surface for
erosion control. Other implements that may be used in heavy residue are stubble
pulverizers or busters (Jacks et al., 1955) and skewtreaders or spike-tooth harrows in conjunction with one-way disk plows (Papendick and Miller, 1977).
Tillage implements that maintain surface residue are (1) s w e e p 6 0 cm or wider;
(2) rodweeders with semichisels or small sweeps; (3) straight-blade machines;
(4) chisel plows; ( 5 ) one-way plows (which generally should be used only when
large amounts of residue are present); and (6) rodweeders. The amount of residue
remaining on the surface after one operation with several tillage machines is
shown in Table 11.
The power needed for stubble mulch tillage depends on such factors as the type
and size of machine; the depth and speed of operation; and the texture, water
content, and slope of soil. Promersberger and Pratt (1958) showed that
Table I1
Effect of Tillage Machines on Surface Residue Remaining after Each Operationa
Tillage machine
Subsurface cultivators
Wide-blade cultivator and rodweeder
Mixing-type cultivators
Heavy-duty cultivator and other type machines
Mixing and inverting disk machines
One-way flexible disk harrow, one-way disk, tandem disk, offset
disk
Inverting machines
Moldboard and inclined disk plow

a From

Anderson ( 1968).

Residue maintained (%)

90
15

50

10


8

P. W . UNGER AND T. M. McCALLA

Table I11
Measured Average Diesel Fuel Consumption for Specific
Field Operations on Pullman Clay h m , Bushland, Texas"

Operation
Dryland
Sweep
Sweep
Surface-irrigated
Moldboard plow
Heavy tandem disk
Heavy offset disk

Lister bedder
Disk bedder
Rolling cultivator
Chisel, 38-cm spacing
Chisel, 50-cm spacing
Chisel, 100-cm spacing
Sweep-rodweed (bed-furrow cultivation)
Seeding
Grain drill, 25-cm spacing

Tillage
depth
(cm)

Diesel
fuel
(liter)

8

6.1
8.4

13

20-25
8-13
8-13

15-20

15-20
15-20

28.1
9.4
11.7
6.5
8.4
5.1
14.0-16.8
12.2
7.5
7.9
3.7

" From Allen er al. (1977).
moldboard plowing and field cultivating (with sweeps) a clay soil at a depth of 13
to 18 cm required 21.4 to 23.2 kW hours/ha (1 1.6 to 12.6 hp hourdacre) and 3.3
to 10 kW hours/ha, respectively. Operating a Noble blade 15 to 27 cm deep
required 10.7 to 13.3 kW hours/ha. Allen et al. (1977) reported fuel consumption values for performing various field operations, including some that are used
in stubble mulch systems, on a clay loam soil (Table 111). Subsurface tillage
generally required less power or fuel than disk or chisel tillage, and substantially
less than moldboard plowing.
Detailed descriptions of implements used in stubble mulch farming systems
were given by Fenster (1960), FA0 (1971), and Jacks et al. (1955). Many types
and sizes of equipment are available for doing a satisfactory job of stubble
mulching. The essential part of any stubble mulching system is to maintain
enough residue on the surface to control erosion adequately from harvest to
harvest.

2 . Reduced- and No-Tillage Systems
One of the major reasons for tilling a soil is to control weeds. Hence, if weeds
are controlled by herbicides, the need for tillage is reduced. The development of


CONSERVATION TILLAGE SYSTEMS

9

effective herbicides in recent years has permitted the development of reduced- and
no-tillage cropping systems. As with stubble mulch tillage, a major goal of
these systems is to maintain crop residue on the surface for soil and water
conservation. In some cases, however, the land is moldboard plowed, but the
number of secondary operations is greatly reduced. The following are reduced- and
no-tillage systems that have been evaluated in research trials and are currently
used by some farmers. Additional information pertaining to these systems is
given by Fisher and Lane (1973), Lewis (1973), Griffith et al. (1977), Amemiya
(19771,Reicosky eral. (1977),Allen etal. (1980), andungerand Wiese(1979).
a . Fall Plow, Field Cultivate. In this system, the moldboard plow is used
for primary tillage, but secondary tillage is reduced to one shallow cultivation
with sweeps at planting. A disk or rotary tiller may be substituted for the field
cultivator to produce a finer, firmer seedbed, but it also leaves the soil more
erodible. This system is widely used on the dark, nearly level, medium- and
fine-textured clay loam soils of the east central Corn Belt.
b. Spring Plow, Wheel-Track Plant. This system uses strip seedbed preparation on soil that was initially plowed 12 to 24 hours before planting. By planting
soon after plowing, the soil water content is such that wheels break the clods and
firm the seedbed. The planted rows may be in the tractor or planter wheel tracks.
This system affords greater protection against erosion than fall plowing because
crop residue is maintained on the surface until planting.
c . Fall Chisel, Field Cultivate. This system is similar to the fall plow, field

cultivate system, except that chiseling 20 to 25 cm deep replaces moldboard
plowing. Chiseling retains more surface residue than moldboard plowing and,
therefore, more effectively controls erosion.
d . Disk and Plant. Tillage in this system is performed with standard tandem
disks operated 8 to 10 cm deep, heavy disks operated 15 to 20 cm deep, or a
combination of the two. The system usually includes one fall disking and one or
more diskings before planting in spring. To conserve surface residue, disking
should be delayed as long as feasible, and tandem disks rather than heavy disks
should be used, because the heavy disks penetrate deeper and incorporate more
residue than do tandem disks.
e . Till-Plant. In this system, tillage and planting are done in one operation.
Normally, tillage is with wide sweeps operated 5 to 8 cm deep on the ridgetop,
which moves old stalks and root clumps into the area between rows and provides
a trash-free zone for planting. The ridges were made the previous year during
cultivation or after harvest with rolling or disk-hiller cultivators, large disk cultivators, or disk bedders (after harvest). Ridges may be re-formed annually in
cases where heavy disks are used to cut residue and level old ridges, or they may
be permanent, in which case the only tillage needed is for reshaping the ridges in
the fall or spring with a rolling or disk-type cultivator.
On soils in the southeast United States with compacted subsurface layers, two


10

P. W . UNGER AND T. M. McCALLA

machines have been developed to loosen the layers and plant seeds directly over
the loosened zone. The first is the “ripper-hipper,” which subsoils the intended
plant row and forms a ridge over the slit with hillers or bedders. Planting can be
done in the same operation. The second machine is the subsoiler-planter, which
has subsoilers to loosen the compacted layer, treading wheels to firm the loose

soil in the slits, and flexible unit planters. Colters can be used with both machines
to cut the surface residue.
f . Strip Tillage. In a strip tillage system, only a narrow band of soil is tilled.
Rotary tillers can be adapted for strip tillage by removing some of the knives.
The tillage zone may be 20 cm wide and 5 to 10 cm deep. A standard planter can
be attached to the tiller, resulting in a one-pass operation, because stalks can be
chopped by the tiller.
Another form of strip tillage is the opening of a slot for seed placement in
previously untilled ground. The system, referred to as no-tillage, zero tillage, or
slot planting, is used to plant in residue of previous crops or in chemically killed
sod. Tillage usually is done with nonpowered, fluted colters running ahead of
planters that have disk openers. Narrow chisels, angled disks, or straight or
slightly rippled colters can also be used to open the soil for seed placement. A
press wheel or seed packer wheel is needed for good seed-soil contact after
planting. For proper operation of no-tillage planters, crop residue should be
uniformly distributed on the soil surface and corn (Zea mays L.) or similar
residue should be chopped before planting.
The equipment and practices just described can be used in various combinations. Some other possibilities are combinations of stubble mulch tillage and
herbicides (Phillips, 1969) and of conventional, reduced, and no-tillage (Allen et
al., 1980; Unger and Wiese, 1979). Choice of system must consider the equipment available, soil and climatic conditions, size and type of farming operation,
and the producer’s managerial ability and personal preferences (Giffith et a l . ,
1977).

B . SEEDBED
PREPARATION
A N D CROPSEEDING

Regardless of crop or region, a firm, moist seedbed is desirable for rapid seed
germination and seedling emergence. In regions with adequate precipitation, the
seedbed normally is moist enough at planting for rapid seed germination and

seedling emergence and for good plant growth. Under such conditions, continuous cropping is possible. In areas of limited precipitation, leaving land idle for a
season to store enough water for a crop may be necessary. This practice is called
summer fallowing. During fallow, the land must be kept free of weeds, and
enough residue must be kept on the surface for erosion control.