Advances in agronomy volume 45

ADVANCES IN

AGRONOMY
VOLUME 45


This Page Intentionally Left Blank


ADVANCES IN

AGRONOMY
Prepured in Cooperation with the
AMERICAN
SOCIETY OF AGRONOMY

VOLUME 45
Edited by Nyle C . Brady
Uniied Nutions Development Programme
Wushington, D . C .

ADVISORY BOARD
G . E. HAM

R. J . KOHEL

G. H . HEICHEL

S . MICKELSON

H . G . HODGES

R. H . MILLER

G . L. HORST

K . H . QUESENBERRY

D. E. KISSEL

C. W. STUBER

E. L. KLEPPER

N . L. TAYLOR

ACADEMIC PRESS, INC.
Harcourt Brace Jovanovich, Publishers
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CONTENTS
CONTRIBUTORS
.............I...........................................................
PREFACE. . . . . . . . . . . . . . . . . . . . . I . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . .

ix

xi

NITROGEN DYNAMICS AND MANAGEMENT IN RICE-LEGUME
CROPPING SYSTEMS

R. J. Buresh and S. K. De Datta
1.
11.

111.
IV.
V.

VI .
VII.

VIII.
IX.

...............................................
Rice Soils .........................
Legumes in Rice-Based Cropping Systems ................ .......................
Effect of Legumes on Soil Nitrogen .....................
Accumulation of Legume Nitrogen .
...........................
Contribution of Legume Nitrogen to Rice ..................................
Effective Management of Legume Nitrogen
Conclusions and Research Needs ....

...............................................

2
3
8
13
16
27
42
44
50
52

PLANT GENETIC RESOURCES: SOME NEW DIRECTIONS

J . T. Williams
I.
11.
111.
IV.
V.

VI.

.........................................
ies ... . .......... . .........
Areas of Research Which Impact Plant Genetic Resources Work ... ......
Sustainability ................. ........... ............ . .........
Current New Directions in Germplasm Management
Concluding Remarks .............. .... . ........ . ............
...............................................
References ....... . ....

61
62
66
81
86
88
89

LONG-TERM IMPACTS OF TILLAGE, FERTILIZER, AND CROP RESIDUE ON SOIL
ORGANIC MATTER IN TEMPERATE SEMIARID REGIONS

Paul E. Rasmussen and Harold P. Collins
1.
11.

Introduction ............ ........., , ., .......... ............. ....,.... ......................
Tillage Effects on Soil Organic Matter .............................................
V

94
99


vi

CONTENTS

111.

IV .
V.
VI .
VII .
VIII .
IX .

X.

Fertilizer Effects on Soil Organic Matter .........................................
..........
Organic Residue Effects on Soil Organic Matter

Organic Matter and Microbial Biomass ...........................................
Management Effects on Physical Properties .............................
Cultivation and Future Change in Soil Organic Matter ........................
Impact of Soil Erosion .................................................................
Predicting Soil Organic Matter Turnover .........................................
Summary ..................................................................................
References ....................
..........................................

102
105
114
119
120
121
123
129
131

EFFICIENT MANAGEMENT OF LEGUMINOUS GREEN MANURES IN WETLAND RICE

Yadvinder Singh. C . S. Khind. and Bijay Singh
I.
I1 .
111.
IV .
V.
VI .
VII .
VIII .

IX .
X.
XI .
XI1 .

Introduction ...............................................................................
Green Manure Crops for Wetland Rice ...
..............................
Biomass and Nitrogen Accumulation in G
nures .....................
Time and Depth of Incorporation of Green Manures ..........................
Yield Responses of Wetland Rice to Green Manuring .......
Nitrogen from Green Manure Crops ...............................................
Transformations of Green Manure Nitrogen in Wetland Rice Soils .......
Effect of Green Manuring on Availability of Plant Nutrients
Other Than Nitrogen .................
.............
..............
Effect of Green Manuring on Soil
ies ....................................
Green Manuring and Reclamation of Saline Alkali Soils ......................
Residual Effects of Green Manures Applied to Wetland Rice .
Conc1us ions ...............................................................................
References .............................
............................

136
137
143

149
151
158
162
166
170
175
177
179
182

ADVANCES IN DISEASE-RESISTANCE BREEDING IN CHICKPEA

K . B . Singh and M . V . Reddy
I.
I1.
111.

IV .
V.
VI .
VII .
VIII .

Introduction ..............................................................
Sources of Genetic Variability .......................................................
Breeding Techniques ................................................
Disease Resistance ......................................................................
Breeding for Multiple Disease Resistance ......................
Annual Wild Cicer Species as a Potential Source of Genes

for Resistance .............................................................
Resistant Cultivars in Disease Management
.............................
Conclusions and Future Needs ..........................................
References ...........
..............................

191
192
193
193
215
216
217
218
219


CONTENTS

vii

GENETICS OF RESISTANCE TO INSECTS IN CROP PLANTS

Gurdev S . Khush and D . S . Brar
I.
I1 .

Introduction ...............................................................................

111.

............................................................
.................
...............
Sorghum ...................................................................................
Barley ......................................................................................
Cotton ...........................
.................................................
Fruits .......................................................................................

IV .
V.
VI .
VII .
VIII .
IX .
X.
XI .
XI1.
XI11.

......

Vegetables .
Forages and Legumes ..................................................................
Tagging Insect Tolerance Genes with Molecular Markers
Genetic Engineering and Insect Tolerance .......................................
Conclusions ........
........................

.................
References ................................................................................

224
226
231
239
243
246
248
252
256
259
262
263
263
265

AGROFORESTRY IN ACID SOILS OF THE HUMID TROPICS

L . T . Szott. C . A . Palm. and P . A . Sanchez
1.
11.
I11.
IV .
V.
v1.

Introduction ...............................................................................
Alley Cropping .................................

........
Managed Fallows ........................................................................
Fruit Crop Food Production Systems ..........
Research Needs ..........................................................................
Summary ..............................................
References
..........
....................................................

275
279
289
294
297
299

300

ASSESSMENT OF AMMONIA VOLATILIZATION FROM FLOODED SOIL SYSTEMS

Gamani R . Jayaweera and Duane S . Mikkelsen
Introduction
...........
..................................................
Theoretical Aspects ..............................
Theory of Ammonia Volatilization .................................................
Factors Affecting Ammonia Volatilization
Methods of Measuring Ammonia Volatilization .................................
Models for Predicting Ammonia Volatilization
Epilogue

...........................................
References ................................................................

303
305
308
310
331
332
353
354

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

357

I.
I1.
I11.
IV .
V.
VI .
VII .


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

D. S. BRAR (223), International Rice Research Institute, 1099 Manila, Philippines
R. J . BURESH ( I ) , Agro-Economic Division, International Fertilizer Development Center, Muscle Shoals, Alabama 35662
HAROLD P. COLLINS (93), U . S . Department of Agriculture, Agricultural Research Service. Columbia Plateau Conservation Research Center, Pendleton,
Oregon 97801
S. K. DE DATTA ( I ) , Agronomy-Physiology-AgroecologyDivision, International
Rice Research Institute, Manila, Philippines
GAMANI R. JAYAWEERA (303), Department of Land, Air and Water Resources, University of California, Davis, California 95616
C . S . KHIND (135), Department of Soils, Punjab Agricultural University, Ludhiana 141 004, India
GURDEV S. KHUSH (223), International Rice Research Institute, 1099 Manila,
Philippines
DUANE S . MIKKELSEN (303), Department of Agronomy and Range Science,
University of California, Davis, California 95616
C. A. PALM (275), Tropical Soils Research Program, Departments of Forestry and Soil Science, North Carolina State University, Raleigh, North Carolina 27695
PAUL E . RASMUSSEN (93), U.S. Department of Agriculture, Agricultural Research Service, Columbia Plateau Conservation Research Center, Pendleton,
Oregon 97801
M. V. REDDY (191), lnternational Crops Research Institute for the Semi-Arid
Tropics (ICRISAT),Patancheru, Andhra Pradesh 502 324, India
P. A. SANCHEZ (273, Tropical Soils Research Program, Departments of Forestry and Soil Science, North Carolina State University, Raleigh, North Carolina 27695
BIJAY SINGH ( 1 3 9 , Department of Soils, Punjab Agricultural University, Ludhiana 141 004, India
K . B . SINGH (191), International Center for Agricultural Research in the Dry
Areas (ICARDA),Aleppo, Syria
YADVINDER SINGH (135), Department of Soils, Punjab Agricultural University, Ludhiana 141 004,India

ix


X

CONTRIBUTORS

L. T. SZOTT' (275), Tropical Soils Research Program, Departments of Forestry and Soil Science, North Carolina State University, Raleigh, North Carolina 27695
J . T. WILLIAMS' (61), International Fund for Agricultural Research (IFAR),
Arlington, Virginia 22209

' Present address: Centro Agronomico Tropical de Investigacidn y Ensenanza (CATIE);
Turrialba, Costa Rica.
* Address correspondence to 161 1 North Kent Street, Suite 600; Arlington, Virginia 22209.


PREFACE
This volume of Advances in Agronomy is the 25th and final volume of
the serial that I have had the privilege of editing. In total, these 25 volumes
have accommodated 195 review articles, as well as the index for the first 30
volumes (Volume 32). Topics have ranged from the chemistry, physics,
biology, and conservation of soils to biochemical genetics, plant breeding,
crop husbandry, crop physiology, cropping systems, and the nutritive
value of crops. About 20,000 research papers were cited by the 339 authors
who helped prepare these reviews. Tens of thousands of agronomists and
soil and crop scientists from around the world have benefitted from these
extensive review efforts.
Special thanks are due to the 339 scientists and educators from 24
countries who prepared these review articles. About half of the authors
were associated with institutions in the United States. Approximately
one-third of these were based at institutions of the federal government and
two-thirds at universities. Forty of the other authors were at Australian
institutions, 20 at institutions in the United Kingdom, 19 in other European
countries, and 15 in Canada. Thirty-two were associated with international
agricultural research centers located mostly in the tropics. Nineteen of the
authors were located at national institutions in developing countries.

These numbers all emphasize the international character of Advances in
Agronomy and the degree to which it has attracted scientists from
throughout the world.
Another group of scientists and educators have contributed greatly to
this serial-those who were kind enough to advise on topics for review and
on potential authors for these reviews. The advisors include 42 scientists
who over the years have served on the Advisory Board of the serial. The
Board of Directors of the American Society of Agronomy also made
valuable suggestions, as did numerous scientists, educators, and administrators from countries around the world. Their advice was invaluable in
seeking out qualified scientists and scholars to prepare articles for this
serial.
Articles in Volume 45 continue the pattern of the previous 24 volumes.
Topics of international interest are covered by scientists from five different
countries. Each of these articles focuses on topics having implications for
long-term sustainable agriculture. Three emphasize nitrogen systems of
wetland areas. Three others emphasize the role of genetic resources,
xi


xii

PREFACE

especially as a means of managing pests by other than chemical means.
Two articles emphasize the role of soil and crop management systems on
soil properties and productivity.
Finally, thanks are due to Academic Press, the publishers of Advances
in Agronomy, for permitting me to serve for nearly 25 years as editor of this
important serial. I wish them and the new editor, Dr. Donald L. Sparks,
the best, as this important serial continues. Its relevance today fully

matches that which prevailed 25 years ago.
NYLEC. BRADY


ADVANCES IN AGRONOMY, VOL. 45

NITROGEN DYNAMICS AND
MANAGEMENT IN RICE-LEGUME
CROPPING SYSTEMS
R. J. Buresh' and S. K. De Datta2
'

Agro-Economic Division
International Fertilizer Development Center
Muscle Shoals, Alabama 35662
* Agronomy-Physiology-Agroecology Division
International Rice Research Institute
Manila, Philippines

I. Introduction
11. Nitrogen Dynamics in Rice Soils
111. Legumes in Rice-Based Cropping Systems
A. Food Legumes
IV .

V.
VI.

VII.
VIII.

IX.

B. Green Manure Legumes
C. Dual-Purpose Legumes
Effect of Legumes on Soil Nitrogen
A. Conservation of Soil N
B. Loss of Soil N
Accumulation of Legume Nitrogen
A. Symbiotic N Fixation
B. N Removal with Legume Grain
Contribution of Legume Nitrogen to Rice
A. Mineralization of Legume N
B. Belowground Legume N
C. Losses of Legume N
D. Residual N Effects
E. Other Factors Contributing to Rice Yield
Effective Management of Legume Nitrogen
Integrated Nitrogen Management
A. Loss of Fertilizer N
B. Effective Use of N Fertilizer
Conclusions and Research Needs
References
1
Copynght 0 1991 by Academic Press. Inc.
All rights of reproduction in any form reserved.


2

R. 3. BURESH AND S. K.DE DATTA

I. INTRODUCTION
More than half of the world’s population of over 5 billion live in Asia,
where rice (Oryza sativa L.)is the staple food of millions of poor people.
To meet the future demand for rice, the International Rice Research
Institute (IRRI, 1989) estimated that the world’s annual rice production
must increase from 458 million t in 1987 to 556 million t by 2000 and to 758
million t by 2020-a 65% increase in 33 years (1.7% per year). This
increase in rice production can only be possible if soil and water resources
and production inputs are used more efficiently in the future.
Rice production increases must attain long-term sustainability with no
adverse environmental impact. Sustaining the necessary rice yield and
production increases in the future will require increased irrigated area and
water use efficiency, more area planted to fertilizer responsive modern
varieties, and development of cost-efficient fertilizer use technology.
Nitrogen is the nutrient most limiting rice production worldwide. In
Asia, where more than 90% of the world’s rice is produced, about 60% of
the N fertilizer consumed is used on rice (Stangel and De Datta, 1985). An
estimated 24% of the increase in Asian rice production from 1965 to 1980
was attributed to use of fertilizer, mainly N (Barker er al., 1985). Despite
past gains in rice production through increased use of industrial N fertilizer, research has demonstrated that industrial N fertilizers generally are
not efficiently utilized by rice and are prone to high losses as N gases (De
Datta and Buresh, 1989). Recent observations of stagnant or declining
yields under continuous rice cropping with high levels of industrial N
fertilizer (Flinn and De Datta, 1984) have raised concerns about the longterm sustainability and possible adverse environmental impacts of monoculture rice receiving high inputs of industrial N fertilizer.
Legumes, with their adaptability to different rice-based cropping patterns and their ability to fix N2, may offer opportunities to increase and
sustain productivity and income in rice-based cropping systems. Food
legumes provide protein for human and animal nutrition as well as economic benefits to farmers because of the high market value for legume
grain and the generally declining real price of rice. Green manure legumes,

forage legumes, and residues from food legumes can supply N to rice,
improve soil physical and chemical properties, and decrease pests and
diseases of rice.
Rice is grown in irrigated and rainfed lowlands, which are characterized
by bunded fields with surface water accumulation, and in uplands, which
are characterized by naturally well-drained soils with no surface water
accumulation. Worldwide, irrigated lowland rice accounts for about 50%


NITROGEN IN RICE-LEGUME CROPPING SYSTEMS

3

of the total rice area and 70% of the total rice production (IRRI, 1989). A
legume can often be included in a rice-rice sequence when climatic conditions, such as cold temperature, and availability of water are not suitable
for rice production. Rainfed lowland rice accounts for about 30% of the
total rice area and about 20% of the total rice production (IRRI, 1989). In
many rainfed lowlands, soil water conditions after a wet-season rice crop
allow growth of a short-duration legume but not a cereal. Upland rice is
smaller in worldwide importance, accounting for about 13% of the land
area and 5% of the production (IRRI, 1989). Legumes can be intercropped,
relay cropped, or grown in sequence with upland rice (Gupta and O’Toole,
1986). Leguminous trees and shrubs offer potential in erosion control and
maintenance or buildup of soil fertility in acid uplands and sloping lands.
Deepwater and tidal wetland rice comprise the remaining 7% of the
world’s rice area (IRRI, 1989). In many deepwater rice areas, legumes can
be grown during the interval between onset of monsoon rain and soil
inundation (Kupkanchanakul et al., 1988).
Nitrogen gains, losses, transformations, and fertilization in continuously flooded lowland rice fields have been extensively researched and
reviewed (De Datta and Patrick, 1986; De Datta and Buresh, 1989). In

contrast, little attention has been given to N transformations and losses
over the longer term in lowland rice fields, which undergo soil drying
between rice crops and soil flooding during rice cropping. Nitrogen accretion and contributions from leguminous green manures in rice-based
cropping systems have attracted increased research interest. However,
less attention has been paid to the role of food legumes in N cycling, gains,
and losses in rice-based cropping systems, even though food legumes are
more commonly grown than green manures in tropical ricelands.
The objective of this article is to review ( 1 ) N dynamics in lowland rice
fields with emphasis on how N dynamics are influenced by typical soil
drying and wetting cycles, (2) the influence of legumes on soil N transformations and N accretion in rice-based cropping systems, (3) the N contribution of legumes to rice, and (4) the integrated management of legume N
and industrial fertilizer N for rice.

II. NITROGEN DYNAMICS IN RICE SOILS
Lowland rice soils typically undergo alternate saturation and drying.
Soils are saturated for at least part of the time during production of rice,
but during intervals between rice crops, the soil usually dries and becomes


4

R. J. BURESH AND S. K. DE DATTA

aerated. At this time, either the soil is left fallow or upland crops are
grown.
In Asia, lowland rice soils are frequently flooded before plowing and
harrowing for rice production. The process of tillage at soil saturation,
referred to as puddling, destroys soil aggregates, reduces downward water
flow and loss of nutrients by leaching, and restricts gaseous exchange
between the soil and the outer atmosphere (Sharma and De Datta, 1986).
The rice crop is established either by transplanting or by broadcasting

germinated seeds on flooded or saturated soil. In environments with a
reliable irrigation supply and low percolation, puddled soils typically remain continuously saturated until just before rice harvest. In rainfed environments and imgated environments with inadequate or irregular water
supply, the soil can undergo alternate drying and rewetting during rice
growth.
An alternative method of rice crop establishment, common in the United
States, is to sow germinated seeds onto nonpuddled, flooded soil. The rice
fields are irrigated and essentially left flooded throughout rice growth
(Westcott and Mikkelsen, 1988).
Some rainfed lowland rice in the tropics and much of the irrigated rice
outside Asia are sown on aerobic, nonpuddled soil. Rice grows as a
dryland crop until sufficient rainwater accumulates for soil submergence
or until permanent flooding by irrigation.
In aerobic soils, ammonium formed from mineralization of organic N or
from N fertilizer can be nitrified to nitrate, which can accumulate in the soil
or be used by plants. When aerobic soils are flooded, soil oxygen is rapidly
depleted and soil nitrate is prone to loss by denitrification and leaching. In
flooded soils, the conversion of ammonium to nitrate is restricted by the
limited supply of soil oxygen; hence, ammonium is the form of mineral N
that accumulates.
At the end of a flooded rice crop, soil nitrate is normally negligible and
soil ammonium, the dominant form of mineral N , is typically low because
of N uptake by rice (Fig. 1). Subsequent drying of the soil favors conversion of ammonium N formed by mineralization to nitrate N. Soil water
status (Linn and Doran, 1984), tillage (Dowdell et al., 1983), and weed
growth (Buresh et al., 1989) influence the accumulation of soil nitrate.
Intermittent rains can stimulate N mineralization and nitrate formation
(Birch, 1958). In a survey of 28 Philippine lowland soils, nitrate N before flooding for rice ranged from 5 to 39 mg/kg and averaged 13 mg/kg
(Ponnamperuma, 1985). In a greenhouse study, Ventura and Watanabe
(1978) reported nitrate N levels of 19 to 35 mg/kg after a dry-season fallow.
Cropping with rice during the dry season decreased nitrate N to 3 mg/kg
before the subsequent wet-season rice crop.

5

NITROGEN IN RICE-LEGUME CROPPING SYSTEMS
Soil aerotion status
Anaerobic

1

7

Rice

N concentration

,-N

loss

FIG. 1. Inorganic N dynamics in lowland rice soils as affected by soil aeration status.

Buresh et al. (1989) showed that substantial quantities of nitrate can
accumulate during the dry season in a mung bean (Vigna radiata [L.]
Wi1czek)-fallow-lowland rice sequence in the Philippines (Fig. 2). At
maturity of late wet-season rice in January, no nitrate was present in the
top 60-cm soil layer. During the subsequent dry-season mung bean crop,
25 and 18 kg nitrate Nlha accumulated in 1986 and 1987, respectively.
Additional nitrate N accumulated during the fallow following mung bean;
52 and 77 kg nitrate N/ha were present in early June immediately before

flooding by imgation for wet-season rice. The soil nitrate rapidly disappeared after flooding. Other researchers (Strickland, 1969; Bacon et al.,
1986) have similarly reported rapid disappearance of nitrate after soil
flooding.
An incubation study with "N-labeled nitrate incorporated into flooded
soil from the study site for the research shown in Fig. 2 revealed that the
added nitrate completely disappeared after 9 days. Only 5% or less of the
added "N-labeled nitrate N remained in the soil as ammonium N and
organic N , indicating that nitrate assimilation and dissimilatory reduction
to ammonium were negligible (Buresh et al., 1989). Denitrification and
leaching appeared to be the mechanisms for nitrate disappearance.


6

R. J. BURESH AND S. K . DE DATTA

FIG.2. Nitrate N in the top 60-cm soil layer during a mung bean-weedy-fallow-lowland
rice sequence in the Philippines. (Adapted from Buresh er al., 1989.)

Buresh et al. (1989) found that soil nitrate N before flooding for wetseason rice correlated inversely with dry matter and N accumulation of
weeds (Fig. 3). Other research in the Philippines has shown significantly
lower soil nitrate levels in weedy fallow than in weed-free fallow before
wet-season rice (unpublished IFDUIRRI collaborative research). Other
studies demonstrated a higher yield of wet-season rice following weedy
fallow than following weed-free fallow (adapted from IRRI, 1986, p. 404):
Grain yield (t/ha)
~

Prerice treatment

No applied N

35 kg N/ha

Weedy fallow
Weed-free fallow

3.2
2.8

3.9
3.3

Lower soil nitrate and higher rice yield following weedy rather than
weed-free fallow suggest that uptake of nitrate N by weeds conserves soil
N from subsequent loss after soil flooding. Nitrate N taken up by weeds is


7

NITROGEN IN RICE-LEGUME CROPPING SYSTEMS
Nitrate N (kg/ha)

*\I

Y =95 -0.56X

r = - 0.80'"

30

Y = 103 -1.89X
r = -0.84* *

0

1

1

I

1

I

I

50

70

90

110

15

20

0

25

.

30

35

Weed N (kg/ha)

Weed dry matter (g/m')

FIG.3. Relationship of nitrate N in the top 60-cm soil layer to weed dry matter and weed
N before soil flooding for wet-season rice in the Philippines. (From Buresh er al., 1989.)

recycled to the soil when weeds are incorporated during land preparation.
The relatively low accumulation of N by weeds growing in tropical ricelands before wet-season rice (Table I) and the appreciable soil nitrate even
at the highest level of weed growth in Fig. 3 suggest that substantial nitrate
N may still accumulate and be lost in traditional weedy fallow-wet-season
rice cropping systems.
The weed biomass incorporated before rice might be an important
source of mineralizable N to flooded rice. Rerkasem and Rerkasem (1984),

Table I

Dry Weight and N Accumulation of Weeds in Unweeded Fallow Plots before Land
Preparation for Wet-Season Rice at Los Baios, Philippines
Aboveground

dry weight
(t/ha)
1.6
1.5

2.1
2.1
1.4

1.7
2.1
2.5

N accumulation
(kdha)
25
21
18
20
I1
12
20
29

C/N
ratio

31

Reference

IRRI (1985, p. 413)
IRRI (1986, p. 403)
IRRI (1986, p. 416)
John (1987)
Alam (1989)
Alam (1989)
Alam (1989)
R. J. Buresh et al. (unpublished)


8

R. J. BURESH AND S. K. DE DATTA

for instance, observed in a heavily weed-infested rice field in Thailand that
removal of weeds before the rice crop resulted in a subsequent rice yield of
2.6 t/ha and a strong response of rice to N fertilizer. Incorporation of
weeds increased yield of unfertilized rice by 40%, and the response to N
fertilizer was less pronounced.

Ill. LEGUMES IN RICE-BASED CROPPING SYSTEMS
Legumes are grown in rice-based cropping systems for protein, oil,
fodder, green manure, and fuel production. In irrigated environments of
the tropics and subtropics, legumes can be grown in rotation with one or
more rice crops per year. In subtropical and temperate regions, where the
growing period for rice is restricted by low temperatures, leguminous
green manures can be grown as the winter crop.
Rice growing areas in tropical Asia are typically monsoonal with a
distinct wet and dry season. In rainfed lowlands, which comprise about
40% of the total rice area in South and Southeast Asia, only one rice crop is

normally possible per year. Production of a second rice crop is limited to
regions with a supplemental water supply or a long, reliable rainy season.
Food legumes can be grown in the postmonsoonal period following rice
when soil water is sufficient (Zandstra, 1982).
A. FOODLEGUMES
Food legumes are a rather minor crop in Asia as compared with cereals.
Yet, they are an important component of Asian farming systems, both in
terms of human and animal nutrition and as a source of biological N. The
ability of legumes to fix N2 enables them to grow on soils with low plantavailable N and to produce high-protein seed and N-rich plant residues.
Yields of food legumes are generally low because they are often grown
with low management and inputs under marginal production conditions, in
which cereals perform poorly or cannot grow. At least 18 food legume
species are considered important at various locations in Asia (Byth et
al., 1987).
The major food legumes grown on ricelands include soybean (Glycine
mux [L.] Merr.), mung bean, groundnut (Aruchis hypogaea [L.]), and
cowpea (Vigna unguicutafa [L.] Walp.). Soybean is an important crop on
ricelands in China, Indonesia, Vietnam, Thailand, and India (Carangal,
1986; Carangal et a / . , 1987). Mung bean is an important crop in India,


NITROGEN IN RICE-LEGUME CROPPING SYSTEMS

9

Thailand, Burma, and Indonesia (Singh, 1988). Cowpea is an important
food legume in Sri Lanka (Singh, 1988). It performs better than other food
legumes on highly acid soil (Pandey and Ngarm, 1985).
In northern India, the production of irrigated mung bean as a third crop
between wheat and rice is increasing (Singh, 1988). However, throughout

tropical Asia most food legume production on lowland rice fields is under
rainfed conditions immediately after an irrigated or rainfed rice crop
(Chandra, 1988; Brotonegoro et af.,1988).
When grown after wet-season lowland rice, legumes can encounter
excess water during the vegetative phase and water deficit during the
reproductive phase (Fig. 4). Postrice legumes depend primarily on residual
soil water, and their roots may follow a receding water table (Timsina,
1989). Mung bean is more sensitive to reproductive-phase and full-season
water deficit than are cowpea and soybean (Pandey et af., 1984; Senthong
and Pandey, 1989). Water deficit reportedly reduces N2 fixation more than
it reduces plant growth and N uptake (Kirda et af., 1989).
When grown immediately before wet-season rice, legumes can encounter water deficit during the vegetative phase and excess water during the
reproductive phase (Timsina, 1989). Soil saturation and temporary waterlogging adversely affect growth, N accumulation, and N2 fixation of food
legumes (Wien et al., 1979; Lawn and Williams, 1987). Soybean is more
tolerant of excess water than is cowpea (Wien et al., 1979; Hulugalle and
Lal, 1986), and cowpea is more tolerant of temporary soil waterlogging
than is mung bean (Minchin and Summerfield, 1976; IRRI, 1985, p. 410).

A

-

-

-

Po st rice

Pre rice

Saturated orflooded soil

FIG.4. Rainfed lowland rice cropping patterns in tropical Asia


10

R. J. BURESH AND S. K. DE DATTA

B. GREENMANURE
LEGUMES
Green manuring with effective N2-fixinglegumes can increase the soil N
pool while also improving soil physical and chemical properties through
the addition of organic matter ( Jiao, 1983). Green manures can be grown in
rice fields before rice and then incorporated during land preparation for
rice. Alternatively, the green manure crop can be grown elsewhere, such
as border areas, nearby upland fields, or levees, and then transported as
cut green matter to the rice field for incorporation. This practice is called
green leaf manuring.
In temperate regions, where temperature restricts the period suitable for
rice, leguminous green manures have historically been grown as a winter
crop in rotation with rice. In China, winter green manures, of which milk
vetch (Astragalus sinicus L.) is the most important, continue to occupy
large areas (Wen, 1989). Milk vetch tolerates cold temperature and shading, but it is sensitive to soil submergence. Milk vetch seeds are normally
broadcast into the field before late rice is harvested in mid-November. In
the following April, part of the vetch is typically removed for forage or
compost and the remainder is directly incorporated as a green manure
(Chen, 1988; Liu, 1988). Alternatively, green manure can be basally applied to rice after composting under waterlogged conditions (Wen, 1989).
Wen (1989) indicated that waterlogged compost can eliminate possible
adverse effects of toxins initially formed during anaerobic decomposition

and provide a steady, long-lasting release of N. However, production and
use of waterlogged compost is labor intensive and N can be lost during
composting.
The use of green manures in rice-based cropping systems has declined
worldwide. In Japan, where milk vetch was formerly an important green
manure, green manures are now of minor importance (Ishikawa, 1988). In
the United States, green manure crops, including vetches and clovers,
have been grown in rotation with rice, but use of green manure crops has
declined to less than 5% of the planted rice area (Westcott and Mikkelsen,
1988). Berseem clover (Trifolium alexandrinum L.) is used as a winter
green manure in Egypt (Hamissa and Mahrous, 1989).
In the tropics, Sesbania species, especially dhaicha IS.cannabina, syn:
S . aculeata), are used as green manure in rice cropping systems. Sesbania
species are well adapted for use as a green manure before rice because of
their ability to withstand soil waterlogging and flooding, to grow on finetextured soils, and to tolerate soil salinity (Evans and Rotar, 1987). Sesbania cannabina and Crotalariajuncea L. (sunn hemp) are common green
manures in India (Abrol and Palaniappan, 1988; Garrity and Flinn, 1988).
The inclusion of a green manure legume between wheat and rice in a


NITROGEN IN RICE-LEGUME CROPPING SYSTEMS

11

rice-wheat rotation in northern India requires irrigation (Singh et
al., 1981). Therefore, in determining the cost effectiveness of green manures in this rotation one must consider the irrigation and fertilization,
particularly phosphorus, required for the green manure.
In a region of the Philippines, indigo (Indigofera tinctoria L.) is grown as
a green manure after wet-season rice in rainfed environments and after a
second rice crop in partially irrigated environments. Normally, it is intercropped with upland food or cash crops. Initial growth of indigo is rather
slow. After the intercrop is removed, the indigo continues growing

throughout the dry season. The indigo is incorporated during land preparation for wet-season rice, and rice is transplanted immediately after biomass incorporation (Bantilan et al., 1989; Garrity et al., 1989).
Woody legume species, particularly Gliricidia sepium ( Jacq.) Steud.,
Leucaena leucocephala (Lam.) de Wit, and Sesbania bispinosa ( Jacq.)
W. F. Wight (syn: S. aculeara, S. cannabina), are used as green leaf
manures in rice-based cropping systems (Brewbaker and Glover, 1988).
When grown near rice fields, these legumes can provide leaf matter for
green manuring as well as for fodder and fuel. Green leaf manure incorporated before transplanting can significantly increase rice yield ( Jeyaraman
and Purushothaman, 1988; Zoysa et al., 1990).
Worldwide, the use of leguminous green manures in rice cropping systems is currently found primarily in irrigated environments. Rainfed rice
environments prone to soil waterlogging appear to have the greatest potential for future green manure cultivation (Garrity and Flinn, 1988). The
recent identification of flood-tolerant, stem-nodulating legumes has increased research interest in green manures for environments prone to
waterlogging (Rinaudo et al., 1988). Sesbania rostrata (Rinaudo et al.,
1983) and Aeschynomene afraspera (Alazard and Becker, 1987) have been
examined in great detail for their potential as green manures.
Production of seed and scarification frequently are constraints in the use
of leguminous green manures, such as S. rostrata. An alternative is to
grow S. rostrata by vegetative propagation (Becker et al., 1988, 1989).
This method requires additional labor to make and plant cuttings, but it
requires less seed, land preparation, and water management.

C. DUAL-PURPOSE
LEGUMES
The quantity of legume N available as a N source for a succeeding rice
crop depends upon N accumulation by the legume and whether it is used
for sole green manuring, seed production, or fodder. Rice farmers are
often reluctant to devote land and resources to growth of legumes solely


12

R. J . BURESH AND S. K. DE DATTA

for green manure because it provides no immediate income or food, yet
requires human labor. Food legumes, in contrast to green manures, offer
the attractive dual benefits of seed production for income or food and
production of residue, which can be used for animal feed or a N source on
the following rice crop (Kulkarni and Pandey, 1988).
Alam (1989) compared cowpea, mung bean, and Sesbania rosfrufuas
prerice crops during the dry-to wet-season transition period in the Philippines. Each crop was sown on two dates and at three sites differing in
internal soil drainage and water table depth. Aboveground biomass remaining after harvest of cowpea and mung bean grain was incorporated.
Grain yields of legumes were adversely affected by soil waterlogging and
heavy rains. Grain yields ranged from 0 to 0.73 t/ha for mung bean and 0 to
0.66 t/ha for cowpea. Mung bean biomass after removal of grain ranged
from 0.2 to 2.5 t/ha and contained 3 to 30 kg N/ha. Cowpea biomass after
removal of grain ranged from 0.5 to 3.9 t/ha and contained 7 to 79 kg N/ha.
Nitrogen accumulation was consistently less for mung bean and cowpea
residue than for S. rosfrata green manure. Rice yields were slightly increased by legume residues and S. rostrata green manure. Whenever soil
drainge and water regime did not prevent production of legume grain, the
economic benefit was greater for mung bean and cowpea than for S.
rostrata because of the high market value for legume grain. Garrity and
Flinn (1988) in a survey of green manure management systems in South,
Southeast, and East Asia concluded that green manures considered only in
terms of N fertilizer savings are currently not economical for rice farmers
in many parts of Asia.
Irrigated mung bean in northern India, grown with recommended management practices for grain production and incorporation of residue, reportedly reduces the industrial N fertilizer requirements on the following
rice crop by 20 to 30 kg N/ha (Chandra, 1988). The benefits of legume
residue are attributed both to direct N effects and improvement of soil
physical properties.
In some regions, legume residues may serve as animal feed. Ruminant
animals are an important source of draft power in many rice-based

cropping systems, but feed for these animals is frequently insufficient,
especially during the dry season. Considerable opportunity still exists for
increasing fodder and forage legume production in tropical rainfed rice
environments (Blair et al., 1986). Recognizing that farmers are often reluctant to grow crops solely for animal feed, Carangal ef al. (1988) proposed postrice intercropping of food legumes or cereals with forage legumes to provide food, fodder, and residue for the next wet-season rice
crop.