Appendix F: Legumes for green manuring and cover-cropping in tropical and subtropical regions

NOTE:

· For additional information, refer to the section on green manures and cover crops in Chapter 10.

· Seed innoculation and cross-innoculation groups: See the section on pulses in Chapter 10 and Table 10-3.

· Before using these species, check first with your country's extension service and experiment stations concerning their experience with them.

Seed scarification: The seeds of some tropical legumes such as centrosema, tropical kudzu, and leucaena have hard, impermeable seed coats which must be broken (scarified) to allow moisture absorption for germination. Several methods can be used:

· Hot water treatment: Soaking for 2-3 minutes at 80°C (176°F) or for 3 seconds in boiling water. Higher temperatures or longer immersions will damage the seed. If such accuracy isn't possible, bring water to a boil, allow to cool for 30 seconds, and then pour it over the seeds, allowing them to soak overnight before planting. Expect in the case of overnight soaking, the heat-treated seeds can be stored for several months or more if quickly air-dried.

· Mechanical means: Seed can be rubbed between sandpaper boards or placed in a drum lined with sandpaper and stirred or rotated to abrade the seed. Leucaena seeds can be nicked with toenail clippers.

I. Quick-Growing Legumes for Short-Term Use (40-90 days)

Glycine max (Soybeans): Annual bush or vining pulse crop requiring 130-160 days for seed production. Moisture needs similar to those of maize. Prefer a soil pH of 6.0-7.0. Varieties are highly daylength-sensitive and must be suited to the local photoperiod. Most varieties are susceptible to nematodes. Prone to diseases when grown in humid conditions. Require a very specific type of rhizobia bacteria.

Phaseolus aureus (Mungbean, Green Gram, Colden Gram): Widely grown in S.E. Asia as a pulse crop; adapted as a short-term green manure/cover crop. Stem-rot resistant but susceptible to nematodes and poor drainage. Fair drought tolerance.

Pueraria acutifolius (Tepary Bean): Annual bushy or viny plant well adapted to hot-dry areas with less than 500 mm annual rainfall and in frequent but heavy rains. Needs good moisture from germination to flowering but can often mature its seed without additional rain. Native to Mexico and Southwest U.S. Only moderately tolerant of salinity and alkalinity, but needs good drainage. Not adapted to humid, high-rainfall conditions. Very resistant to common bean blight (a bacterial disease; Xanthomonas phaseoli). Mature seeds are produced in 60-90 days after plant emergence. Dry seeds are edible after soaking and boiling; references disagree as to flavor ("strong-tasting", "mild-flavored"). Leaves and pods can be fed to livestock.

Sesbania macrocarpa (Syn. S. exaltata) [Coffeeweed]: Quick-growing, erect annual suitable as a green manure. Susceptible to nematodes. Can become invasive if allowed to set seed.

Vigna unguiculata (Syn. V. sinensis) [Cowpea]: Grown for edible seeds and young pods, forage, green manuring, and cover cropping. Varieties range in growth habit from bushy determinates (seed produced over a short period) to viny indeterminates (seed produced over several months>. Best adapted to 400-1500 mm annual rainfall. Well adapted to semiarid regions. Better tolerance to heat, drought, and soil acidity than common beans (Phaseolus vulgaris). Poor tolerance of soil salinity. Requires good drainage. Some varieties have good root knot nematode resistance. Makes good hay. Seed matures 60-200 days after planting with bush types being the earliest. V. sesquipedalis (yardlong bean, asparagus bean) is a closely related species widely grown in Asia. Nodulates readily.

II. Bush or Viny Legumes Suited for Long-Term Use (90 days +)

Calopogonium mucunioides (Calopo): Short-lived, vigorus, climbing perennial suited to hot, humid tropical areas with rainfall over 1500 mm. Not very palatable to livestock but may be eaten during dry season.

Clitoria ternatea (Butterfly Pea): Very drought tolerant; small leaved and doesn't cover the ground well. Grows in Central America at sea level.

Canavalia ensiformis (Jack Bean): A bushy, semi-erect annual 60-120 cm tall; can become a perennial climber; adapted to annual rainfall as low as 650-750 mm; fairly drought tolerant once established; tolerant of acid soils; withstands some waterlogging. Forage palatable to livestock only when dried and needs gradual introduction. Young leaves and pods can be eaten after cooking. The dried seeds are unattractive in flavor and must be soaked and boiled in salted water for several hours to soften them and remove toxins; they can also be detoxified by fermenting into tempeh. Produces green, immature pods in 90-120 days after sowing and mature seeds in 180-300 days.

Canavalia gladiata (Sword Bean): Vigorous perennial climber reaching 4-10 m in length; can be treated as an annual. Grows best under 900-1500 mm annual rainfall; once established, it has some drought tolerance. Most varieties have only poor to fair tolerance of waterlogging. Tolerant of acid soils. Forage palatable to livestock only when dried. Immature green pods widely used as green beans in Asia; mature seeds contain toxins which require soaking and boiling to remove and have a strong flavor and thick, tough seedcoat.

Centrosema pubescens (Centrosema, Centro): Aggressive vining perennial that readily climbs. Best for areas having over 1000 mm rainfall. Tolerant of acid soils and has some tolerance of poor drainage. Moderately palatable to livestock. Seed innoculation recommended as its rhizobia bacteria is somewhat strain-specific. If seeding conditions are secure, the seeds should be scarified with hot water to assure uniform germination. Some varieties can be propagated by stem cuttings. Withstands fairly heavy grazing.

Crotalaria spp.: Most species are erect annual or perennial shrubs reaching 90-180 cm. Green forage, hay, and silage of C. juncea (sunn hemp) and C. spectabilis (showy crotalaria, rattlebox) are toxic to livestock; seeds of all types are toxic. Best adapted to sandy soils and well-drained areas.

Desmodium intortum (Greenleaf Desmodium): Vining perennial best adapted to 900-1500 mm rainfall. Tolerant of acidic soils and waterlogging. Very palatable to livestock. Best as a grazed cover crop. Established by seed or stem cuttings.

Desmodium uncinatum (Silverleaf Desmodium): Lower tolerance to drought and waterlogging than greenleaf but withstands light frosts. Excellent forage. Best as a grazed cover crop.

Dolichos lablab (Lablab Bean, Hyacinth bean): Vigorous annual or biennial vining plants that make good forage. Flowers, leaves, and dried seeds are edible for humans. Adapted to areas with 500-2500 mm rainfall; needs good moisture for establishment. Good tolerance to acid soils and to aluminum toxicity, but needs good drainage. Crows well wherever cowpeas do but has better disease and insect resistance, though it is susceptible to nematodes. Seeds mature in 150-200 days and are unusually large, making them ideal for rough seedbed conditions. Competes well with weeds during establishment. Seeds mature 150-200 days after sowing. Withstands rotational grazing but cattle require time to adapt to it.

Indigofera hirsute (Hairy indigo): Annual shrub growing to 1.2-2 m. Adapted to acid, sandy soils. Makes good hay if cut before 90 cm. Has suppressant effect on root knot nematodes. Nodulates readily with cowpea rhizobia group.

Phaseolus atropurpureus (Siratro): Deep-rooted perennial used mainly for pasture. Best adapted to 750-2000 mm rainfall but has good drought tolerance. Requires good drainage. Resistant to nematodes. Reacts to stress by shedding its leaves. Easily established by seed; stem cuttings can also be used. Nodulates readily with cowpea rhizobia. Susceptible to Rhizoctonia stem rot in high rainfall regions.

Phaseolus lathyroides (Phasey bean): Self-regenerating (by seed fall) annual or bienniel erect plants eventually developing vines. Best adapted to subtropical areas with over 750 mm rainfall. Fair tolerance to waterlogging but susceptible to nematodes. Tolerant of acid, infertile soils. Forage is palatable to livestock. Nodulates readily with cowpea rhizobia.

Phaseolus lunatus (Lima bean): There are 2 groups of lima beans: bushy-erect and tropical vining. Unlike the bushy-erect types, the tropical vining types are especially well adapted to hot-humid conditions and are often the principal pulse crop of the wet rainforest regions of Africa and Latin America; unlike the bushy types, the vining types are efficient nitrogen fixers. However, they are susceptible to nematodes, have poor drought tolerance, and don't do well below a soil pH of 6.0. Seeds, immature pods, and leaves are eaten, but some varieties (especially those with dark-colored seeds) have toxic levels of hydrocyanic acid in these parts which must be removed by boiling and changing the cooking water.

Pueraria phaseoloides (Tropical Kudzu, Puero): Vigorous vining perennial with stems up to 8 m ions" Best adapted to ample rainfall (over 1500 mm). Tolerant of acid soils and somewhat tolerant of poor drainage. Very palatable to livestock and withstands moderate grazing. Fair drought tolerance. Established by seed which should be soaked for 24 hours or treated with hot water. Stem cuttings can also be used. Not to be confused with common (Japanese) kudzu, which is a much more aggressive subtropical species.

Stizolobium spp. (Syn. Mucuna pruriens) [Velvet Bean]: A vigorous annual or perennial climbing vine for forage and green manuring/cover cropping. Best adapted to 1200-1500+ mm of rainfall; not as drought tolerant as C. ensiformis. Grows from sea level to 2000 m in the tropics. Well adapted to sandy, less fertile soils. Fair tolerance of soil acidity but require good drainage. Seed produced in 180-270 days, although the few early-maturing varieties require just 110-130 days. Seeds are unusable for poultry but can be fed up to the 25% level to pigs. Seeds eaten by humans but require soaking and boiling to remove a toxin. Toasted, ground seeds used as a coffee substitute. Some varieties have an irritating, itchy powder on the pods. Relatively free from insect attack but susceptible to some species of root knot nematode. Nodulates with cowpea rhizobia.

Stylosanthes guyanensis (Stylo): A perennial erect small shrub growing up to 1.5 m. Best adapted to rainfall above 900 mm. Very tolerant of low fertility and acid soils but responds well to added P where lacking; sensitive to copper deficiency. Some tolerance of poor drainage. Good livestock forage but less resistant to heavy grazing than centro or siratro. Palatability varies but improves as growth progresses. Not very drought resistant but can re-establish itself through self-sown seed. Established by seed which needs scarification. All varieties except Schofield require a specific strain of rhizobia bacteria.

Stylosanthes humilis (Townsville Stylo): A self-regenerating (through reseeding) annual or biennial erect shrub whose branches can reach 90 cm in length. Needs at least 600 mm annual rainfall. Well adapted to low fertility and acid soils and is a good P extractor. Needs good drainage. Palatable to livestock and makes good hay. Withstands grazing well.

III. Legume Trees and Shrubs Suited for Cut-and-Carry Green Manuring

DANGER: Some of the the species below, such as Sesbania bispinosa, are aggressive and quick-growing; they may become invasive. Use native species of known behavior whenever possible.

Cajanus cajan (Pigeon pea): Short-lived perennial shrub often grown as annual since seed yield declines after the first year. Used for cut-and-carry green manuring, soil improvement, forage, firewood, and for its edible seeds and young pods. Deep rooted and drought tolerant. Best adapted to annual rainfall of 600-1000 mm. Requires good drainage. Some tolerance to salinity. Mature seed produced 100-250 days after sowing. Can be cropped for 2-3 years, but yields decline quickly after that. Can be maintained up to 5 years as a forage or green manure crop. Some varieties susceptible to root knot nematodes. Readily nodulates with cowpea rhizobia.

Calliandra calothyrsus (Calliandra): A small tree (up to 10 m tall) used for firewood, erosion control, windbreaks, cut-and-carry green manuring, and beautification. Reaches 2.5-3.5 m in 6-9 months. Best adapted to rainfall over 1000 mm but withstands several months of drought. Some tolerance of poor drainage. Competes well with weeds. Coppices (regrows) readily after cutting. Established by seed or large cuttings. Nodulates freely with cowpea rhizobia. Seed needs hot water treatment.

Gliricidia septum (Madre de Cacao, Quickstick, Madera Negra): A quick-growing tree for timber, live fencing, shade, forage, cut-and-carry green manuring, and honey foraging. Best adapted to rainfalls of 1500-2300 mm. Leaves are palatable to cattle but poisonous to most other animals. Roots, bark, and seeds are toxic; leaves can be toxic to humans. Leaves drop during dry season. Coppices (regrows) readily after cutting; can be trimmed every 1-2 months. Established by seed or large cuttings which readily root.

Leucaena leucocephala (Leucaena, Ipil-Ipil): Multi-purpose, deep-rooted shrub or tree suitable for cut-and-carry green manuring. Best adapted to areas below 500 m elevation with 500-2000 mm rainfall. Needs good drainage and a soil pH of 5.0 or above. Can be seriously attacked by psyllid insects (jumping plant lice). Makes slow initial growth and is easily wiped out by weeds, termites, ants, and rodents. Growth becomes very rapid after the first few weeks and can reach 4-6 m in 12 months. Quickly regrows new foliage within 2-3 weeks. Its high-protein leaf forage contains mimosine which is toxic to non-ruminants unless fed at low levels. Some low-mimosine leaucaena varieties have been identified. Innoculation with leaucaena-specific rhizobia is sometimes recommended. However, the Nat. Academy of Sciences states that seed innoculation isn't normally needed even when leucaena is planted on new ground, especially if other leguminous trees like Calliandra, Gliricidia, Sesbania, and Mimosa are present; however, specific rhizobia strains for Leucaena are now available. Seed scarification is needed for good germination, due to the hard seed coat. Other uses: firewood, edible seeds, poles, reforestation, living fence. Can become an aggressive weed.

Mimosa scabrella: Rapid-growing thornless tree used for firewood, beautification, live fencing, and cut-and-carry green manure. Can reach 5 m height in 14 months. Native to the cool subtropical savanna of S.E. Brazil but can grow in warmer areas; stunted by wet soils. Good nitrogen fixer.

Sesbania bispinosa (Prickly Sesban): Quick-growing shrub up to 4 m tall that can produce firewood in 6 months. Good drought tolerance but does best at 550-1100 mm rainfall and up to 1200 m elevation. Good tolerance of saline and alkaline soils. Tolerates wet soils but not long periods of waterlogging. Palatable to cattle. Suitable for cut-and-carry green manuring. Can become an invasive weed due to its abundant seed production. Freely nodulates with cowpea rhizobia.

Sesbania grandiflora (Agati, Katurai, West Indian Pea Tree): Small, fast-growing tree up to 10 m tall. Used for firewood, reforestation, forage, food, and cut-and-carry green manure. Best adapted to rainfall over 1000 mm and elevations below 800 m. Adapted to wide range of soils; some tolerance to waterlogging. Very susceptible to nematodes. Young leaves, young pods, and giant flowers are popular vegetables in Asia. Established by seed. Freely nodulates with cowpea rhizobia group.

Sesbania sesban (Sesban): Fast-growing, short-lived shrub 4.5-6 m tall used for wood, forage, food, and green manure. Requires 350-1000 mm rainfall. Tolerates acid soils, saline soils, and periodic waterlogging. Forage is very palatable. Regrows readily after cutting. Flowers, leaves, and seeds are edible for humans; seeds require soaking and cooking to remove a toxin. Widely used in the tropics as a green manure for rice and should be turned under at least 3 weeks before transplanting. In double-crop rice areas, it can be interplanted at a late stage of the first crop and then used as a green manure for the second crop.