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
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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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