TECHNICAL PAPER #38
UNDERSTANDING LEGUME CROPS
By
Dr. Carl S. Hoveland
Technical Reviewers
Dr. Janice Coffey
James A. Duke
Dr. Martin L. Price
Donald R. Sumner
Published By
VOLUNTEERS IN TECHNICAL ASSISTANCE
1600 Wilson Boulevard, Suite 500, Arlington, Virginia 22209 USA
Telephone: (703) 276-1800, Fax: (703) 243-1865
Telex: 440192 VITAUI, Cable: VITAINC
Internet: vita@gmuvax.gmu.edu, Bitnet: vita@gmuvax
Understanding Legume Crops
ISBN: 0-86619-250-6
[C] 1985, Volunteers in Technical Assistance
PREFACE
This paper is one of a series published by Volunteers in Technical
Assistance to provide an introduction to specific state-of-the-art
technologies of interest to people in developing countries.
The papers are intended to be used as guidelines to help
people choose technologies that are suitable to their situations.
They are not intended to provide construction or implementation
details. People are urged to contact VITA or a similar organization
for further information and technical assistance if they
find that a particular technology seems to meet their needs.
The papers in the series were written, reviewed, and illustrated
almost entirely by VITA Volunteer technical experts on a purely
voluntary basis. Some 500 volunteers were involved in the production
of the first 100 titles issued, contributing approximately
5,000 hours of their time. VITA staff included Betsey Eisendrath
as editor, Suzanne Brooks handling typesetting and layout,
and Margaret Crouch as project manager.
The author of this paper, VITA Volunteer Dr. Carl S. Hoveland, is
a Professor of Agronomy at the University of Georgia College of
Agriculture in Athens, Georgia. The reviewers are also VITA
volunteers. Dr. Janice Coffey is a professor with the Department
of Science at Saint Mary's College in Raleigh, North Carolina.
James A. Duke is the Research Leader for the Germplasm Resources
Laboratory of the United States Department of Agriculture in
Beltsville, Maryland. Dr. Martin L. Price is the Executive Director
of ECHO, Inc. --Educational Concerns for Hunger Organization,
located in North Fort Myers, Florida. Donald R. Sumner is a
Professor of Plant Pathology at the University of Georgia in
Tifton, Georgia.
VITA is a private, nonprofit organization that supports people
working on technical problems in developing countries. VITA offers
information and assistance aimed at helping individuals and
groups to select and implement technologies appropriate to their
situations. VITA maintains an international Inquiry Service, a
specialized documentation center, and a computerized roster of
volunteer technical consultants; manages long-term field projects;
and publishes a variety of technical manuals and papers.
UNDERSTANDING LEGUMES
by VITA Volunteer Carl S. Hoveland
I. INTRODUCTION
The two groups of plants of greatest importance to world agriculture
are grasses (such as maize, wheat, rice, sorghum, pearl millet,
sugar cane, and forage grasses) and legumes (such as peas,
beans, soybeans, alfalfa, clovers, cowpeas). Legumes are extremely
important because of the high nutritive quality of the
seeds for human and animal food and of the entire plant for
ruminant animal feed, and because of their ability to fix atmospheric
nitrogen in a form usable by plants, thus reducing the
need for nitrogen fertilizer.
Legumes were grown by ancient civilizations in China, Europe,
the Middle East, and Central and South America. However, it was
not until the late 1800s in Germany that it was understood how
bacteria growing in association with legumes could accomplish the
remarkable task of collecting atmospheric nitrogen and making it
available for other growing plants.
Legumes are used mainly as
o grains for human and animal food;
o forage for cattle, sheep, camels, goats and rabbits;
o oilseeds (especially soybeans and peanuts); and
o green manure to improve the yield of other crops in
rotation systems.
Although legumes are widely grown throughout the world, there is
a great opportunity for expanded usage, especially in the tropics
and subtropics where nitrogen fertilizer is lacking and protein
deficiency is a serious problem in human and animal populations.
The legume family name, Leguminosae, is derived from the term
legume, which is the name of the fruit (often called a pod)
characteristic of this group of plants. A legume is a fruit that
contains a single row of seeds and breaks open along the ribs of
the pod. Legumes may be annuals (completing their life cycle in
one year) or perennials. Legume species vary greatly in other
respects. Leaves may be compound or simple. Stems vary in
length, size, branching, and woodiness. Most legumes have tap-roots.
Most, but not all, have nitrogen-fixing bacteria associated
with their roots. Flowers, often brightly colored, also
vary, but the most common type has five petals on each flower.
The flowers are often clustered in dense heads as on white or red
clover. Figure 1 shows the leaves, flower structure, and fruit
09p02.gif (600x600)
pod of the hyacinth bean (Dolichos lablab), a common legume.
There are over 11,000 species of legumes in the world. They
include tropical shrubs (indigo), trees (locust and mesquite),
vines (kudzu), and herbs (clover and vetch). Most of the economically
important cool season legumes, such as clovers, peas,
lupines, vetch, and alfalfa, originated in the Mediterranean and
Middle Eastern area. Soybeans, lespedeza, velvet bean, and adzuki
bean are native to China. A number of pulses such as pigeon
pea, guar, winged bean, and mung bean are native to Southeast
Asia. Cowpeas and hyacinth bean are native to Africa. Peanut or
groundnut, lima and common bean, centro, tick clover, stylo, and
many other tropical legumes are native to Central and South
America.
NITROGEN FIXATION
Most legumes have the unique capacity to fix atmospheric nitrogen
and make it available for plant growth. Bacteria of the genus
Rhizobium infect the root hairs of legume seedlings, causing the
formation of a swelling on the root. This swelling is called a
nodule. The process is shown in Figure 2. The nodule bacteria
09p04.gif (600x600)
take their energy from the legume plant, which in turn receives
nitrogen that has been fixed (made available by the bacteria).
This ability to fix nitrogen allows the plant to meet its nitrogen
needs even when soil nitrogen is limited. This mutually
beneficial association is called nitrogen fixation. It happens
when the bacteria cause the nitrogen to combine chemically with
hydrogen to form ammonia, and ultimately amino acids and plant
protein. Legumes are vitally important in agriculture because of
their high protein content and their independence of soil nitrogen
resources.
Effective nitrogen-fixing nodules can easily be identified by
their bright red color when sliced open with a knife. Legumes
may also be infected with non-nitrogen-fixing nodules, which lack
the red color. In this case, nitrogen fixation will not take
place unless the plant is infected with the proper strain of
bacteria.
The association between legume species and rhizobial strain is
often highly specific. One bacterial strain is able to infect
the root system and produce effective nodules on one group of
legumes but not on legumes of another species. For instance,
rhizobia that are effective on soybean are not effective on
alfalfa. Even within the clover species, certain rhizobial
strains are specific to one clover species. Many tropical legumes
also have specific bacterial strains. Figure 3 shows the root
09p05.gif (600x600)
nodules associated with certain representative legumes.
When the proper strain for a particular legume species is not
present in the soil, it is essential to inoculate the plant with
this strain by adding the specific rhizobial strain to the legume
seed at planting.
Successful inoculation of legume seeds depends on several
factors:
1. The proper rhizobial strain is applied to the legume
seed at planting. Commercial inoculants may be available
in peat-based mixtures.
2. The bacteria are sensitive to heat, so inoculum should
be stored in a cool place until used.
3. A syrup or molasses-water mix should be used to moisten
the seed before applying the inoculum. This holds the
inoculum on the seed.
4. Hot, dry conditions after planting will kill many of
the bacteria. Planting in moist soil or just before
rain will greatly improve survival of the bacteria.
Pelleting the seed with gum arabic and inoculum will
also improve survival in hot, dry soils.
5. Most of the non-tropical legume species require
adequate lime or calcium in the soil for the rhizobia
to survive and infect the legume plant. Tropical
species are generally more tolerant of soil acidity.
III. SUCCESSFUL LEGUME CULTIVATION
CLIMATIC REQUIREMENTS
Legume species must be adapted to local weather conditions,
though irrigation can compensate for insufficient rainfall. Legumes
such as white or red clover are best adapted to regions
where the temperature will remain moderate during the period of
active growth. Other legumes, such as alfalfa, can withstand
high atmospheric temperature provided soils are not waterlogged.
Tropical species such as indigo, centro, and stylo are tolerant
of high temperature and high humidity. In regions where the
climate is mild and wet in winter, and hot and dry in summer,
annual cool-season legumes such as arrowleaf, crimson, subterranean
clovers, or peas are better suited. In tropical climates
with wet summers and dry winters, summer annuals such as soybean,
cowpeas, peanuts, or pigeon peas may be desirable.
SOIL REQUIREMENTS
In developed countries, soils are generally modified by liming
and fertilization to grow a particular legume successfully.
Alfalfa, which is intolerant of soil acidity, often requires
heavy applications of lime. Other legumes such as cowpeas, red
clover, soybeans, and subterranean clover are more tolerant of
soil acidity. Tropical legumes are generally quite tolerant of
soil acidity. Peanuts, tolerant of soil acidity, do require
adequate calcium in the soil zone where flowers form pegs.
Sericea lespedeza is very tolerant of acidity and of the toxic
aluminum often found in tropical soils.
Tropical soils, in addition to being acid, are often very low in
phosphorus; where fertilizers are not readily available or are
too expensive, it may be necessary to choose a legume that is
tolerant of low levels of phosphorus. Because low potassium
levels also often limit the growth of legumes, fertilization may
be needed. Trace elements such as boron, manganese, zinc, or
molybdenum may also be needed in small quantitites.
Poor soil drainage may restrict the oxygen available to plant
roots. This problem increases at higher temperatures. Selection
of legume species tolerant of poor drainage can overcome this
problem to some extent. Strawberry and ladino clovers are
tolerant of poor drainage while alfalfa, red clover, and crimson
clovers require well-drained soil.
ESTABLISHMENT AND MANAGEMENT OF LEGUMES
It is essential to select a legume species adapted to the
particular climate and soil. Even when this is done, failures
may occur during the critical establishment period. The following
checklist may be useful in ascertaining the cause of failure.
1. Failure of seed to germinate in the soil.
o Dead seed. Germination declines in old seed. Poorly
stored seed increases the problem.
o Dry seedbed. Seeds have a high water requirement for
germination. A well-prepared seedbed provides better
soil-seed contact and can assist in surrounding the
seed with sufficient moisture for seed germination.
o Hard or dormant seed. Many legume species have hard
seedcoats. These will not germinate unless the seedcoats
are scratched or scarified to allow water to
penetrate. This problem is particularly serious in
many small-seeded legumes such as arrowleaf clover or
vetch, and in many trees. (Seeds may be scarified by
tumbling them in a container with course sand.)
o Unfavorable temperature. Warm season legume species
such as soybeans, cowpeas, peanuts, and alyce clover
have a higher temperature requirement than cool season
species such as ladino, crimson, and arrowleaf clovers,
or alfalfa.
o Soil-borne pathogens. Fungi and bacteria may rot
seeds.
2. Early emergence failures. (The seed germinates but fails to
emerge from the soil.)
o Overly deep planting. Small-seeded legumes such as
ladino or white clover should not be planted more than
1 to 2 centimeters deep. In contrast, large-seeded
legumes such as soybeans, peanuts, peas, or beans can
be planted deeper.
o Soil crusting. This is often a problem in high
temperature areas of the tropics and subtropics where
soil organic matter is very low. The crust physically
prevents emergence of the seedling. Adding organic
matter to the soil or providing a mulch can reduce the
crusting problem.
o Insects. Insects may destroy seedlings, especially
those of small-seeded legumes planted in grass sods.
It may be necessary to apply insecticides for control
of crickets and other insects in grass sods.
o Extremes of temperatures. Extremely high temperatures
or freezes may kill small legume seedlings.
o Soil-borne pathogens. Fungi, bacteria, or nematodes
may kill germinated seeds before emergence.
3. Early seedling stage failures.
o Soil acidity, low fertility, or poor physical
conditions.
o Insects or diseases.
o Drought.
o Poor nodulation of roots with nitrogen-fixing bacteria.
o Weed competition.
o Damage from cold in winter.
Subsequent management of legumes depends on the legume species
and the use made of them. Adequate supplies of soil phosphorus
and potassium are essential for many of the most productive
legumes. Various root and leaf diseases, nematodes, and insects
may sharply reduce production unless they are controlled. Before
applying a pesticide, it is important to determine if it can be
safely used on a particular food or forage crop, and how soon
after application the crop may be harvested or grazed.
IV. LEGUME SPECIES BY MAJOR USE
The three primary uses for legumes are as food grains and seeds
for people and lifestock; as forage for livestock; and as a green
manure to improve the yield of other crops in rotation. This
section lists some of the major legumes in each of these
categories and briefly describes their cultural characteristics.
LEGUMES FOR FOOD
There are a large number of warm- and cool-season annual legumes
that are important for grain or vegetable production. Others are
of minor importance, while yet others could be food crops but are
not cultivated.
The legumes most widely used for food are:
Soybean Peanut Cowpea
Green bean Lima bean Broad bean
Adzuki bean Mung bean Winged bean
Carob Chickpea Lentil
Lupine Green pea Pigeon pea
Hyacinth bean Moth bean Tepary bean
Tamarind
LEGUMES FOR FORAGE
A large number of legume species are used for grazing and hay.
These are divided into season cool annuals and perennials and
warm season annuals and perennials.
Cool season annuals:
Arrowleaf clover - no bloat problems in livestock, long
productive season.
Ball clover - tolerant of wet soils.
Berseem clover - tolerant of high temperature during seed
germination, no bloat.
Crimson clover - vigorous early growth, early maturity.
Persian clover - tolerant of wet soils.
Rose clover - drought-tolerant.
Strawberry clover - tolerant of wet soils and salt.
Subterranean clover - tolerant of hard grazing by sheep.
Hairy vetch - very cold-tolerant.
Common vetch - high winter productivity in mild climates.
Rough pea - tolerant of wet soils.
Cool season perennials:
Alfalfa or lucerne - highest yielding forage legume, long
productive season.
Red clover - short-lived productive legume tolerant of soil
acidity.
Ladino clover - very tolerant of close grazing, long prductive
season.
Bird's-foot trefoil - non-bloating legume tolerant of acid soils.
Cicer milk vetch - tolerant to drought and alkaline soils.
Sainfoin - tolerant of drought, low phosphorus, and alkaline
soils.
White clover - tolerant of close grazing.
Warm season annuals:
Alyce clover - high quality but susceptible to nematodes.
Annual lespedeza - tolerant of low soil fertility, low forage
yield.
Hairy indigo - tolerant of low soil fertility, resistant to
nematodes, mildly toxic.
Joint vetch - tolerant of soil acidity, productive.
Phasemy bean - leafy shrub that reseeds well in tropical areas.
Townsville lucerne - reseeding leafy shrub, tolerant of low
fertility, well adapted to Australian tropics.
Warm season perennials:
Sericea lespedeza - highly productive, very tolerant of soil
acidity and low fertility.
Perennial peanut - productive, tolerates grazing well, tolerant
of acidity.
Centro - high quality viny shrub that grows well with grasses in
tropics.
Stylo - tolerant of low fertility, not tolerant of drought or
frost.
Lotononis - creeping-type plant that tolerates grazing well.
Leucaena - shrub that can be grazed while it continues to supply
nitrogen to associated grasses in tropics.
LEGUMES FOR GREEN MANURE IN ROTATION
Many soils, particularly in the tropics and subtropics, are low
in nitrogen. Legume crops, grown in rotation with other crops
can be used to add nitrogen to the soil. The amount of nitrogen
fixed annually by rhizobia varies with legume species:
Legume kg N/hectare
Alfalfa 200-400
Ladino clover 100-200
Lupines 100-150
Red clover 100-150
Crimson clover 100
Cowpeas 100
Vetch 90
Annual lespedeza 80
Soybeans 50-100
Peas 60
Peanuts 40
Beans 40
The nitrogen in the nodules, top growth, and roots of the legume
becomes available for use by other plants growing with the legume
or growing in the same soil later. Approximately 80 percent of
the nitrogen is in the uncut top growth, and 20 percent is in
the roots. Nitrogen usually averages 3.5 percent of the plant
material on a dry matter base.
Maximum availability of nitrogen from legumes usually occurs
within two months after the legume blooms. Thus, the full-bloom
stage is a good time to plow under a legume crop to obtain a
substantial quantity of nitrogen to enrich the soil for the next
crop. Where a winter annual legume such as crimson clover is
grown, as in the southeastern United States, the amount of nitrogen
fixed in the soil is adequate to produce an excellent grain
sorghum crop following the clover, with no additional nitrogen
fertilizer.
Legumes normally used in rotation with other crops are:
Cool Season Annuals: Cool Season Perennials:
Crimson clover Alfalfa
Berseem clover Red clover
Vetch
Annual sweet clover
Lupines
Warm Season Annuals:
Sesbania
Pigeon peas
Velvet beans
Cowpeas
Sword bean (Canavalia gladiata)
LEGUMES
Adzuki bean Vigna angularis
Alfalfa Midicago sativa
Alyce clover Alysicarpus vaginalis
Arrowleaf clover Trifloium vesiculosum
Ball clover Trifolium nigrescens
Beans Phaseolus vulgaris
Berseem clover Trifolium alexandrinum
Bird's-foot trefoil Lotus corniculatus
Broad bean Vicia faba
Carob Ceratonia siliqua
Centro Centrosema pubescens
Chickpea Cicer arietinum
Clover Trifolium spp.
Common vetch Vicia sativa
Cowpea Vigna sinensis
Crimson clover Trifolium incarnatum
Egyptian clover. See Berseem clover
Fenugreek Trigonella foenum-graecum
French bean. See Bean
Garbanzo. See Chickpea
Green pea. See Pea
Groundnut. See Peanut
Guar Cyamopis tetragonolabus
Hairy indigo Indigofera hirsuta
Hairy vetch Vicia villosa
Haricot bean. See Bean
Hyacinth bean Dolichos lablab
Indigo Indigofera spp.
Jack bean Canovalia ensiformis
Joint vetch Aeschynomene americana
Kidney bean. See Bean
Kudzu Pueraria lobata
Ladino clover. See White clover
Lentil Lens culinaris
Lespedeza Lespedeza spp.
Leucaena Leucaena leucocephala
Licorice Glycyrrhiza
Lima bean Phaseolus lunatus
Lucerne. See Alfalfa
Lupine Lupinus spp.
Mesquite Prosopsis juliflora,
P. glandulosa,
P. chilensis, others
Mimosa Mimosa spp.
Moth bean Vigna aconitfolia
Mung bean Vigna radiata
Peanut Arachis hypogaea
Pea Pisum sativum
Persian clover Trifolium resupinatum
Phasemy bean Phaseolus semirectus,
Phaseolus lathyroides
Pigeon pea Cajanus cajan
Red clover Trifolium pratense
Rose clover Trifolium hirtum
Rough pea Lathyrus hirsutus
Sainfoin Onobrychis viciifolia
Scarlet runner Phaseolus coccineus
Sericea lespedeza Lespedeza cuneata
Sesbania Sesbania exaltata
Snap bean. See Bean
Soybean Glycine max
Strawberry clover Trifolium fragiferum
String bean. See Bean
Stylo Stylosanthes spp.
Subterranean clover Trifolium subterraneum
Tamarind Tamarindus indica
Tepary bean Phaseolus acutifolia
Velvet bean Mucuna deeringiana
Vetch Vicia spp.
White clover Trifolium repens
Winged bean Phosphocarpus
tetragonolobus
Winter vetch. See Hairy vetch
========================================
========================================
UNDERSTANDING LEGUME CROPS
By
Dr. Carl S. Hoveland
Technical Reviewers
Dr. Janice Coffey
James A. Duke
Dr. Martin L. Price
Donald R. Sumner
Published By
VOLUNTEERS IN TECHNICAL ASSISTANCE
1600 Wilson Boulevard, Suite 500, Arlington, Virginia 22209 USA
Telephone: (703) 276-1800, Fax: (703) 243-1865
Telex: 440192 VITAUI, Cable: VITAINC
Internet: vita@gmuvax.gmu.edu, Bitnet: vita@gmuvax
Understanding Legume Crops
ISBN: 0-86619-250-6
[C] 1985, Volunteers in Technical Assistance
PREFACE
This paper is one of a series published by Volunteers in Technical
Assistance to provide an introduction to specific state-of-the-art
technologies of interest to people in developing countries.
The papers are intended to be used as guidelines to help
people choose technologies that are suitable to their situations.
They are not intended to provide construction or implementation
details. People are urged to contact VITA or a similar organization
for further information and technical assistance if they
find that a particular technology seems to meet their needs.
The papers in the series were written, reviewed, and illustrated
almost entirely by VITA Volunteer technical experts on a purely
voluntary basis. Some 500 volunteers were involved in the production
of the first 100 titles issued, contributing approximately
5,000 hours of their time. VITA staff included Betsey Eisendrath
as editor, Suzanne Brooks handling typesetting and layout,
and Margaret Crouch as project manager.
The author of this paper, VITA Volunteer Dr. Carl S. Hoveland, is
a Professor of Agronomy at the University of Georgia College of
Agriculture in Athens, Georgia. The reviewers are also VITA
volunteers. Dr. Janice Coffey is a professor with the Department
of Science at Saint Mary's College in Raleigh, North Carolina.
James A. Duke is the Research Leader for the Germplasm Resources
Laboratory of the United States Department of Agriculture in
Beltsville, Maryland. Dr. Martin L. Price is the Executive Director
of ECHO, Inc. --Educational Concerns for Hunger Organization,
located in North Fort Myers, Florida. Donald R. Sumner is a
Professor of Plant Pathology at the University of Georgia in
Tifton, Georgia.
VITA is a private, nonprofit organization that supports people
working on technical problems in developing countries. VITA offers
information and assistance aimed at helping individuals and
groups to select and implement technologies appropriate to their
situations. VITA maintains an international Inquiry Service, a
specialized documentation center, and a computerized roster of
volunteer technical consultants; manages long-term field projects;
and publishes a variety of technical manuals and papers.
UNDERSTANDING LEGUMES
by VITA Volunteer Carl S. Hoveland
I. INTRODUCTION
The two groups of plants of greatest importance to world agriculture
are grasses (such as maize, wheat, rice, sorghum, pearl millet,
sugar cane, and forage grasses) and legumes (such as peas,
beans, soybeans, alfalfa, clovers, cowpeas). Legumes are extremely
important because of the high nutritive quality of the
seeds for human and animal food and of the entire plant for
ruminant animal feed, and because of their ability to fix atmospheric
nitrogen in a form usable by plants, thus reducing the
need for nitrogen fertilizer.
Legumes were grown by ancient civilizations in China, Europe,
the Middle East, and Central and South America. However, it was
not until the late 1800s in Germany that it was understood how
bacteria growing in association with legumes could accomplish the
remarkable task of collecting atmospheric nitrogen and making it
available for other growing plants.
Legumes are used mainly as
o grains for human and animal food;
o forage for cattle, sheep, camels, goats and rabbits;
o oilseeds (especially soybeans and peanuts); and
o green manure to improve the yield of other crops in
rotation systems.
Although legumes are widely grown throughout the world, there is
a great opportunity for expanded usage, especially in the tropics
and subtropics where nitrogen fertilizer is lacking and protein
deficiency is a serious problem in human and animal populations.
The legume family name, Leguminosae, is derived from the term
legume, which is the name of the fruit (often called a pod)
characteristic of this group of plants. A legume is a fruit that
contains a single row of seeds and breaks open along the ribs of
the pod. Legumes may be annuals (completing their life cycle in
one year) or perennials. Legume species vary greatly in other
respects. Leaves may be compound or simple. Stems vary in
length, size, branching, and woodiness. Most legumes have tap-roots.
Most, but not all, have nitrogen-fixing bacteria associated
with their roots. Flowers, often brightly colored, also
vary, but the most common type has five petals on each flower.
The flowers are often clustered in dense heads as on white or red
clover. Figure 1 shows the leaves, flower structure, and fruit
09p02.gif (600x600)
pod of the hyacinth bean (Dolichos lablab), a common legume.
There are over 11,000 species of legumes in the world. They
include tropical shrubs (indigo), trees (locust and mesquite),
vines (kudzu), and herbs (clover and vetch). Most of the economically
important cool season legumes, such as clovers, peas,
lupines, vetch, and alfalfa, originated in the Mediterranean and
Middle Eastern area. Soybeans, lespedeza, velvet bean, and adzuki
bean are native to China. A number of pulses such as pigeon
pea, guar, winged bean, and mung bean are native to Southeast
Asia. Cowpeas and hyacinth bean are native to Africa. Peanut or
groundnut, lima and common bean, centro, tick clover, stylo, and
many other tropical legumes are native to Central and South
America.
NITROGEN FIXATION
Most legumes have the unique capacity to fix atmospheric nitrogen
and make it available for plant growth. Bacteria of the genus
Rhizobium infect the root hairs of legume seedlings, causing the
formation of a swelling on the root. This swelling is called a
nodule. The process is shown in Figure 2. The nodule bacteria
09p04.gif (600x600)
take their energy from the legume plant, which in turn receives
nitrogen that has been fixed (made available by the bacteria).
This ability to fix nitrogen allows the plant to meet its nitrogen
needs even when soil nitrogen is limited. This mutually
beneficial association is called nitrogen fixation. It happens
when the bacteria cause the nitrogen to combine chemically with
hydrogen to form ammonia, and ultimately amino acids and plant
protein. Legumes are vitally important in agriculture because of
their high protein content and their independence of soil nitrogen
resources.
Effective nitrogen-fixing nodules can easily be identified by
their bright red color when sliced open with a knife. Legumes
may also be infected with non-nitrogen-fixing nodules, which lack
the red color. In this case, nitrogen fixation will not take
place unless the plant is infected with the proper strain of
bacteria.
The association between legume species and rhizobial strain is
often highly specific. One bacterial strain is able to infect
the root system and produce effective nodules on one group of
legumes but not on legumes of another species. For instance,
rhizobia that are effective on soybean are not effective on
alfalfa. Even within the clover species, certain rhizobial
strains are specific to one clover species. Many tropical legumes
also have specific bacterial strains. Figure 3 shows the root
09p05.gif (600x600)
nodules associated with certain representative legumes.
When the proper strain for a particular legume species is not
present in the soil, it is essential to inoculate the plant with
this strain by adding the specific rhizobial strain to the legume
seed at planting.
Successful inoculation of legume seeds depends on several
factors:
1. The proper rhizobial strain is applied to the legume
seed at planting. Commercial inoculants may be available
in peat-based mixtures.
2. The bacteria are sensitive to heat, so inoculum should
be stored in a cool place until used.
3. A syrup or molasses-water mix should be used to moisten
the seed before applying the inoculum. This holds the
inoculum on the seed.
4. Hot, dry conditions after planting will kill many of
the bacteria. Planting in moist soil or just before
rain will greatly improve survival of the bacteria.
Pelleting the seed with gum arabic and inoculum will
also improve survival in hot, dry soils.
5. Most of the non-tropical legume species require
adequate lime or calcium in the soil for the rhizobia
to survive and infect the legume plant. Tropical
species are generally more tolerant of soil acidity.
III. SUCCESSFUL LEGUME CULTIVATION
CLIMATIC REQUIREMENTS
Legume species must be adapted to local weather conditions,
though irrigation can compensate for insufficient rainfall. Legumes
such as white or red clover are best adapted to regions
where the temperature will remain moderate during the period of
active growth. Other legumes, such as alfalfa, can withstand
high atmospheric temperature provided soils are not waterlogged.
Tropical species such as indigo, centro, and stylo are tolerant
of high temperature and high humidity. In regions where the
climate is mild and wet in winter, and hot and dry in summer,
annual cool-season legumes such as arrowleaf, crimson, subterranean
clovers, or peas are better suited. In tropical climates
with wet summers and dry winters, summer annuals such as soybean,
cowpeas, peanuts, or pigeon peas may be desirable.
SOIL REQUIREMENTS
In developed countries, soils are generally modified by liming
and fertilization to grow a particular legume successfully.
Alfalfa, which is intolerant of soil acidity, often requires
heavy applications of lime. Other legumes such as cowpeas, red
clover, soybeans, and subterranean clover are more tolerant of
soil acidity. Tropical legumes are generally quite tolerant of
soil acidity. Peanuts, tolerant of soil acidity, do require
adequate calcium in the soil zone where flowers form pegs.
Sericea lespedeza is very tolerant of acidity and of the toxic
aluminum often found in tropical soils.
Tropical soils, in addition to being acid, are often very low in
phosphorus; where fertilizers are not readily available or are
too expensive, it may be necessary to choose a legume that is
tolerant of low levels of phosphorus. Because low potassium
levels also often limit the growth of legumes, fertilization may
be needed. Trace elements such as boron, manganese, zinc, or
molybdenum may also be needed in small quantitites.
Poor soil drainage may restrict the oxygen available to plant
roots. This problem increases at higher temperatures. Selection
of legume species tolerant of poor drainage can overcome this
problem to some extent. Strawberry and ladino clovers are
tolerant of poor drainage while alfalfa, red clover, and crimson
clovers require well-drained soil.
ESTABLISHMENT AND MANAGEMENT OF LEGUMES
It is essential to select a legume species adapted to the
particular climate and soil. Even when this is done, failures
may occur during the critical establishment period. The following
checklist may be useful in ascertaining the cause of failure.
1. Failure of seed to germinate in the soil.
o Dead seed. Germination declines in old seed. Poorly
stored seed increases the problem.
o Dry seedbed. Seeds have a high water requirement for
germination. A well-prepared seedbed provides better
soil-seed contact and can assist in surrounding the
seed with sufficient moisture for seed germination.
o Hard or dormant seed. Many legume species have hard
seedcoats. These will not germinate unless the seedcoats
are scratched or scarified to allow water to
penetrate. This problem is particularly serious in
many small-seeded legumes such as arrowleaf clover or
vetch, and in many trees. (Seeds may be scarified by
tumbling them in a container with course sand.)
o Unfavorable temperature. Warm season legume species
such as soybeans, cowpeas, peanuts, and alyce clover
have a higher temperature requirement than cool season
species such as ladino, crimson, and arrowleaf clovers,
or alfalfa.
o Soil-borne pathogens. Fungi and bacteria may rot
seeds.
2. Early emergence failures. (The seed germinates but fails to
emerge from the soil.)
o Overly deep planting. Small-seeded legumes such as
ladino or white clover should not be planted more than
1 to 2 centimeters deep. In contrast, large-seeded
legumes such as soybeans, peanuts, peas, or beans can
be planted deeper.
o Soil crusting. This is often a problem in high
temperature areas of the tropics and subtropics where
soil organic matter is very low. The crust physically
prevents emergence of the seedling. Adding organic
matter to the soil or providing a mulch can reduce the
crusting problem.
o Insects. Insects may destroy seedlings, especially
those of small-seeded legumes planted in grass sods.
It may be necessary to apply insecticides for control
of crickets and other insects in grass sods.
o Extremes of temperatures. Extremely high temperatures
or freezes may kill small legume seedlings.
o Soil-borne pathogens. Fungi, bacteria, or nematodes
may kill germinated seeds before emergence.
3. Early seedling stage failures.
o Soil acidity, low fertility, or poor physical
conditions.
o Insects or diseases.
o Drought.
o Poor nodulation of roots with nitrogen-fixing bacteria.
o Weed competition.
o Damage from cold in winter.
Subsequent management of legumes depends on the legume species
and the use made of them. Adequate supplies of soil phosphorus
and potassium are essential for many of the most productive
legumes. Various root and leaf diseases, nematodes, and insects
may sharply reduce production unless they are controlled. Before
applying a pesticide, it is important to determine if it can be
safely used on a particular food or forage crop, and how soon
after application the crop may be harvested or grazed.
IV. LEGUME SPECIES BY MAJOR USE
The three primary uses for legumes are as food grains and seeds
for people and lifestock; as forage for livestock; and as a green
manure to improve the yield of other crops in rotation. This
section lists some of the major legumes in each of these
categories and briefly describes their cultural characteristics.
LEGUMES FOR FOOD
There are a large number of warm- and cool-season annual legumes
that are important for grain or vegetable production. Others are
of minor importance, while yet others could be food crops but are
not cultivated.
The legumes most widely used for food are:
Soybean Peanut Cowpea
Green bean Lima bean Broad bean
Adzuki bean Mung bean Winged bean
Carob Chickpea Lentil
Lupine Green pea Pigeon pea
Hyacinth bean Moth bean Tepary bean
Tamarind
LEGUMES FOR FORAGE
A large number of legume species are used for grazing and hay.
These are divided into season cool annuals and perennials and
warm season annuals and perennials.
Cool season annuals:
Arrowleaf clover - no bloat problems in livestock, long
productive season.
Ball clover - tolerant of wet soils.
Berseem clover - tolerant of high temperature during seed
germination, no bloat.
Crimson clover - vigorous early growth, early maturity.
Persian clover - tolerant of wet soils.
Rose clover - drought-tolerant.
Strawberry clover - tolerant of wet soils and salt.
Subterranean clover - tolerant of hard grazing by sheep.
Hairy vetch - very cold-tolerant.
Common vetch - high winter productivity in mild climates.
Rough pea - tolerant of wet soils.
Cool season perennials:
Alfalfa or lucerne - highest yielding forage legume, long
productive season.
Red clover - short-lived productive legume tolerant of soil
acidity.
Ladino clover - very tolerant of close grazing, long prductive
season.
Bird's-foot trefoil - non-bloating legume tolerant of acid soils.
Cicer milk vetch - tolerant to drought and alkaline soils.
Sainfoin - tolerant of drought, low phosphorus, and alkaline
soils.
White clover - tolerant of close grazing.
Warm season annuals:
Alyce clover - high quality but susceptible to nematodes.
Annual lespedeza - tolerant of low soil fertility, low forage
yield.
Hairy indigo - tolerant of low soil fertility, resistant to
nematodes, mildly toxic.
Joint vetch - tolerant of soil acidity, productive.
Phasemy bean - leafy shrub that reseeds well in tropical areas.
Townsville lucerne - reseeding leafy shrub, tolerant of low
fertility, well adapted to Australian tropics.
Warm season perennials:
Sericea lespedeza - highly productive, very tolerant of soil
acidity and low fertility.
Perennial peanut - productive, tolerates grazing well, tolerant
of acidity.
Centro - high quality viny shrub that grows well with grasses in
tropics.
Stylo - tolerant of low fertility, not tolerant of drought or
frost.
Lotononis - creeping-type plant that tolerates grazing well.
Leucaena - shrub that can be grazed while it continues to supply
nitrogen to associated grasses in tropics.
LEGUMES FOR GREEN MANURE IN ROTATION
Many soils, particularly in the tropics and subtropics, are low
in nitrogen. Legume crops, grown in rotation with other crops
can be used to add nitrogen to the soil. The amount of nitrogen
fixed annually by rhizobia varies with legume species:
Legume kg N/hectare
Alfalfa 200-400
Ladino clover 100-200
Lupines 100-150
Red clover 100-150
Crimson clover 100
Cowpeas 100
Vetch 90
Annual lespedeza 80
Soybeans 50-100
Peas 60
Peanuts 40
Beans 40
The nitrogen in the nodules, top growth, and roots of the legume
becomes available for use by other plants growing with the legume
or growing in the same soil later. Approximately 80 percent of
the nitrogen is in the uncut top growth, and 20 percent is in
the roots. Nitrogen usually averages 3.5 percent of the plant
material on a dry matter base.
Maximum availability of nitrogen from legumes usually occurs
within two months after the legume blooms. Thus, the full-bloom
stage is a good time to plow under a legume crop to obtain a
substantial quantity of nitrogen to enrich the soil for the next
crop. Where a winter annual legume such as crimson clover is
grown, as in the southeastern United States, the amount of nitrogen
fixed in the soil is adequate to produce an excellent grain
sorghum crop following the clover, with no additional nitrogen
fertilizer.
Legumes normally used in rotation with other crops are:
Cool Season Annuals: Cool Season Perennials:
Crimson clover Alfalfa
Berseem clover Red clover
Vetch
Annual sweet clover
Lupines
Warm Season Annuals:
Sesbania
Pigeon peas
Velvet beans
Cowpeas
Sword bean (Canavalia gladiata)
LEGUMES
Adzuki bean Vigna angularis
Alfalfa Midicago sativa
Alyce clover Alysicarpus vaginalis
Arrowleaf clover Trifloium vesiculosum
Ball clover Trifolium nigrescens
Beans Phaseolus vulgaris
Berseem clover Trifolium alexandrinum
Bird's-foot trefoil Lotus corniculatus
Broad bean Vicia faba
Carob Ceratonia siliqua
Centro Centrosema pubescens
Chickpea Cicer arietinum
Clover Trifolium spp.
Common vetch Vicia sativa
Cowpea Vigna sinensis
Crimson clover Trifolium incarnatum
Egyptian clover. See Berseem clover
Fenugreek Trigonella foenum-graecum
French bean. See Bean
Garbanzo. See Chickpea
Green pea. See Pea
Groundnut. See Peanut
Guar Cyamopis tetragonolabus
Hairy indigo Indigofera hirsuta
Hairy vetch Vicia villosa
Haricot bean. See Bean
Hyacinth bean Dolichos lablab
Indigo Indigofera spp.
Jack bean Canovalia ensiformis
Joint vetch Aeschynomene americana
Kidney bean. See Bean
Kudzu Pueraria lobata
Ladino clover. See White clover
Lentil Lens culinaris
Lespedeza Lespedeza spp.
Leucaena Leucaena leucocephala
Licorice Glycyrrhiza
Lima bean Phaseolus lunatus
Lucerne. See Alfalfa
Lupine Lupinus spp.
Mesquite Prosopsis juliflora,
P. glandulosa,
P. chilensis, others
Mimosa Mimosa spp.
Moth bean Vigna aconitfolia
Mung bean Vigna radiata
Peanut Arachis hypogaea
Pea Pisum sativum
Persian clover Trifolium resupinatum
Phasemy bean Phaseolus semirectus,
Phaseolus lathyroides
Pigeon pea Cajanus cajan
Red clover Trifolium pratense
Rose clover Trifolium hirtum
Rough pea Lathyrus hirsutus
Sainfoin Onobrychis viciifolia
Scarlet runner Phaseolus coccineus
Sericea lespedeza Lespedeza cuneata
Sesbania Sesbania exaltata
Snap bean. See Bean
Soybean Glycine max
Strawberry clover Trifolium fragiferum
String bean. See Bean
Stylo Stylosanthes spp.
Subterranean clover Trifolium subterraneum
Tamarind Tamarindus indica
Tepary bean Phaseolus acutifolia
Velvet bean Mucuna deeringiana
Vetch Vicia spp.
White clover Trifolium repens
Winged bean Phosphocarpus
tetragonolobus
Winter vetch. See Hairy vetch
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