TECHNICAL PAPER #38
UNDERSTANDING LEGUME CROPS
Dr. Carl S. Hoveland
Dr. Janice Coffey
James A. Duke
Dr. Martin L. Price
Donald R. Sumner
VOLUNTEERS IN TECHNICAL ASSISTANCE
Boulevard, Suite 500, Arlington, Virginia 22209 USA
Telephone: (703) 276-1800,
Fax: (703) 243-1865
Telex: 440192 VITAUI,
Understanding Legume Crops
Volunteers in Technical Assistance
This paper is one of a series published by Volunteers in
Assistance to provide an introduction to specific
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
They are not intended to provide construction or
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
almost entirely by VITA Volunteer technical experts on a
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.
a Professor of Agronomy at the University of Georgia College
Agriculture in Athens, Georgia.
The reviewers are also VITA
Janice Coffey is a professor with the Department
of Science at Saint Mary's College in Raleigh, North
James A. Duke is the Research Leader for the Germplasm
Laboratory of the United States Department of Agriculture in
Dr. Martin L. Price is the Executive Director
of ECHO, Inc. --Educational Concerns for Hunger
located in North Fort Myers, Florida.
Donald R. Sumner is a
Professor of Plant Pathology at the University of Georgia in
VITA is a private, nonprofit organization that supports
working on technical problems in developing countries.
information and assistance aimed at helping individuals and
groups to select and implement technologies appropriate to
maintains an international Inquiry Service, a
specialized documentation center, and a computerized roster
volunteer technical consultants; manages long-term field
and publishes a variety of technical manuals and papers.
VITA Volunteer Carl S. Hoveland
The two groups of plants of greatest importance to world
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
nitrogen in a form usable by plants, thus reducing the
need for nitrogen fertilizer.
Legumes were grown by ancient civilizations in China,
the Middle East, and Central and South America.
However, it was
not until the late 1800s in Germany that it was understood
bacteria growing in association with legumes could
remarkable task of collecting atmospheric nitrogen and
available for other growing plants.
Legumes are used mainly as
grains for human and animal food;
forage for cattle, sheep, camels, goats and
oilseeds (especially soybeans and peanuts);
green manure to improve the yield of other
Although legumes are widely grown throughout the world,
a great opportunity for expanded usage, especially in the
and subtropics where nitrogen fertilizer is lacking and
deficiency is a serious problem in human and animal
The legume family name, Leguminosae, is derived from the
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
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
The flowers are often clustered in dense heads as on white
clover. Figure 1
shows the leaves, flower structure, and fruit
pod of the hyacinth bean (Dolichos lablab), a common legume.
There are over 11,000 species of legumes in the world.
include tropical shrubs (indigo), trees (locust and
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
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
Asia. Cowpeas and
hyacinth bean are native to Africa.
groundnut, lima and common bean, centro, tick clover, stylo,
many other tropical legumes are native to Central and South
Most legumes have the unique capacity to fix atmospheric
and make it available for plant growth.
Bacteria of the genus
Rhizobium infect the root hairs of legume seedlings, causing
formation of a swelling on the root.
This swelling is called a
nodule. The process
is shown in Figure 2. The nodule
take their energy from the legume plant, which in turn
nitrogen that has been fixed (made available by the
This ability to fix nitrogen allows the plant to meet its
needs even when soil nitrogen is limited.
beneficial association is called nitrogen fixation.
when the bacteria cause the nitrogen to combine chemically
hydrogen to form ammonia, and ultimately amino acids and
protein. Legumes are
vitally important in agriculture because of
their high protein content and their independence of soil
Effective nitrogen-fixing nodules can easily be identified
their bright red color when sliced open with a knife.
may also be infected with non-nitrogen-fixing nodules, which
the red color. In
this case, nitrogen fixation will not take
place unless the plant is infected with the proper strain of
The association between legume species and rhizobial strain
often highly specific.
One bacterial strain is able to infect
the root system and produce effective nodules on one group
legumes but not on legumes of another species.
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
nodules associated with certain representative legumes.
When the proper strain for a particular legume species is
present in the soil, it is essential to inoculate the plant
this strain by adding the specific rhizobial strain to the
seed at planting.
Successful inoculation of legume seeds depends on several
The proper rhizobial strain is applied to
planting. Commercial inoculants may be
The bacteria are sensitive to heat, so
in a cool place until used.
A syrup or molasses-water mix should be
used to moisten
before applying the inoculum. This
Hot, dry conditions after planting will
kill many of
bacteria. Planting in moist soil or
greatly improve survival of the bacteria.
the seed with gum arabic and inoculum will
improve survival in hot, dry soils.
Most of the non-tropical legume species
lime or calcium in the soil for the rhizobia
to survive and infect the legume
generally more tolerant of soil acidity.
Legume species must be adapted to local weather conditions,
though irrigation can compensate for insufficient
such as white or red clover are best adapted to regions
where the temperature will remain moderate during the period
active growth. Other
legumes, such as alfalfa, can withstand
high atmospheric temperature provided soils are not
Tropical species such as indigo, centro, and stylo are
of high temperature and high humidity.
In regions where the
climate is mild and wet in winter, and hot and dry in
annual cool-season legumes such as arrowleaf, crimson,
clovers, or peas are better suited.
In tropical climates
with wet summers and dry winters, summer annuals such as
cowpeas, peanuts, or pigeon peas may be desirable.
In developed countries, soils are generally modified by
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
Tropical legumes are generally quite tolerant of
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
aluminum often found in tropical soils.
Tropical soils, in addition to being acid, are often very
phosphorus; where fertilizers are not readily available or
too expensive, it may be necessary to choose a legume that
tolerant of low levels of phosphorus.
Because low potassium
levels also often limit the growth of legumes, fertilization
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
roots. This problem
increases at higher temperatures.
of legume species tolerant of poor drainage can overcome
problem to some extent.
Strawberry and ladino clovers are
tolerant of poor drainage while alfalfa, red clover, and
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.
checklist may be useful in ascertaining the cause of
1. Failure of seed
to germinate in the soil.
Germination declines in old seed.
increases the problem.
Seeds have a high water requirement for
germination. A well-prepared
seedbed provides better
contact and can assist in surrounding the
sufficient moisture for seed germination.
Hard or dormant seed.
Many legume species have hard
seedcoats. These will not
germinate unless the seedcoats
scratched or scarified to allow water to
penetrate. This problem is
particularly serious in
small-seeded legumes such as arrowleaf clover or
in many trees. (Seeds may be scarified
them in a container with course sand.)
Warm season legume species
soybeans, cowpeas, peanuts, and alyce clover
higher temperature requirement than cool season
as ladino, crimson, and arrowleaf clovers,
Fungi and bacteria may rot
2. Early emergence
failures. (The seed germinates but
emerge from the
Overly deep planting.
Small-seeded legumes such as
white clover should not be planted more than
1 to 2
centimeters deep. In contrast,
as soybeans, peanuts, peas, or beans can
This is often a problem in high
areas of the tropics and subtropics where
matter is very low. The crust
emergence of the seedling. Adding
the soil or providing a mulch can reduce the
Insects may destroy seedlings, especially
small-seeded legumes planted in grass sods.
It may be
necessary to apply insecticides for control
and other insects in grass sods.
Extremes of temperatures.
Extremely high temperatures
may kill small legume seedlings.
Fungi, bacteria, or nematodes
germinated seeds before emergence.
3. Early seedling
Soil acidity, low fertility, or poor
Insects or diseases.
Poor nodulation of roots with
Damage from cold in winter.
Subsequent management of legumes depends on the legume
and the use made of them.
Adequate supplies of soil phosphorus
and potassium are essential for many of the most productive
root and leaf diseases, nematodes, and insects
may sharply reduce production unless they are
applying a pesticide, it is important to determine if it can
safely used on a particular food or forage crop, and how
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
for people and lifestock; as forage for livestock; and as a
manure to improve the yield of other crops in rotation.
section lists some of the major legumes in each of these
categories and briefly describes their cultural
LEGUMES FOR FOOD
There are a large number of warm- and cool-season annual
that are important for grain or vegetable production.
of minor importance, while yet others could be food crops
The legumes most widely used for food are:
Lima bean Broad
Mung bean Winged
Green pea Pigeon
Moth bean Tepary
LEGUMES FOR FORAGE
A large number of legume species are used for grazing and
These are divided into season cool annuals and perennials
warm season annuals and perennials.
Cool season annuals:
Arrowleaf clover - no bloat problems in livestock, long
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
Red clover - short-lived productive legume tolerant of soil
Ladino clover - very tolerant of close grazing, long
Bird's-foot trefoil - non-bloating legume tolerant of acid
Cicer milk vetch - tolerant to drought and alkaline soils.
Sainfoin - tolerant
of drought, low phosphorus, and alkaline
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
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
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,
Centro - high quality viny shrub that grows well with
Stylo - tolerant of low fertility, not tolerant of drought
Lotononis - creeping-type plant that tolerates grazing well.
Leucaena - shrub that can be grazed while it continues to
nitrogen to associated grasses in tropics.
LEGUMES FOR GREEN MANURE IN ROTATION
Many soils, particularly in the tropics and subtropics, are
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:
The nitrogen in the nodules, top growth, and roots of the
becomes available for use by other plants growing with the
or growing in the same soil later.
Approximately 80 percent of
the nitrogen is in the uncut top growth, and 20 percent is
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
crop. Where a winter
annual legume such as crimson clover is
grown, as in the southeastern United States, the amount of
fixed in the soil is adequate to produce an excellent grain
sorghum crop following the clover, with no additional
Legumes normally used in rotation with other crops are:
Cool Season Annuals:
Cool Season Perennials:
Warm Season Annuals:
Egyptian clover. See
French bean. See
Green pea. See Pea
Haricot bean. See
Kidney bean. See
Ladino clover. See
Lucerne. See Alfalfa
P. chilensis, others
Snap bean. See Bean
String bean. See
Winter vetch. See