Chapter 4
Agroforestry

4.3 Leguminous cover crops

Leguminous cover crops (LCCs) are planted as a living mulch, to control erosion and keep weeds out. Many species are nutritious forages. When plowed under, they provide large amounts of organic material, nitrogen, and available phosphorus to the soil.

Leguminous cover crops can be used to suppress existing Imperata (Section 4.3.1).

They are most useful to prevent Imperata from growing back after it has been controlled (Section 4.3.2). Legumes are often planted as an intercrop, a relay crop, or a fallow crop.

Dead and dry leguminous vines can burn. At the beginning of the dry season, press the vines and Imperata to make them less flammable. Press the vines even where there is no Imperata. Fire and uncontrolled grazing are important constraints to the use of cover crops.

4.3.1 Establishing leguminous cover crops to suppress Imperata

To suppress Imperata before crops or trees are planted, choose an aggressive species. Use a variety with a short life (for example, Mucuna pruriens var. utilis) if another crop will be planted soon. Use a mixture including species with a longer life (for example, Centrosema or Pueraria) if cover is needed for a longer time. Use a mixture including a drought-tolerant species if there is a distinct dry season. Use good quality seed.

Leguminous cover crops to suppress Imperata

Strategy: seed leguminous cover crops directly into Imperata

Suggest if:

• Land is not needed for 1-2 years

• Low-input method for suppressing Imperata is needed

1. Choose a perennial species, such as Pueraria phaseoloides.

2. Broadcast pods or seeds in the Imperata. Use about 2-3 kg seeds/hectare.

3. Press the grass and vines at the beginning of the dry season or when the grass grows upright and becomes a fuel hazard, and at the beginning of the rainy season, when the vine begins to climb on the Imperata.

4. Kill the cover crop when the Imperata has been suppressed and it is time to plant annual crops. Mucuna and Pueraria can be slashed and left to dry and die. Their residue provides an excellent mulch.

5. Plant crops 1-2 weeks after slashing or 2-3 weeks after plowing under the residues.

Treatment of leguminous cover crops (LCC)

Direct seeding of leguminous cover crops in Imperata

"Hapi-hapi" in Cebu, Philippines. Farmers in Cebu use this method in /mperaia-infested coconut plantations to improve soil fertility and nut production. They sow 2-3 kg/ ha of Puemria phaseoloides seeds (or the equivalent in pods) and then burn the Imperata to give the Pueraria a quick start. They press after six months and at least once more during the first year. Within two years, the Imperata is controlled and the farmers plant additional crops under the coconuts.

Northern Vietnam. Farmers in upland areas rehabilitate Imperata grasslands by sowing rice bean (Phaseolus carcaratus) in previously burned fields. Two to three crops of edible beans are produced in 1-2 years with hand weeding. Yields are low but the Imperata is suppressed. The bean's leaves are a good fodder. Other crops are then planted, and rice bean is often used as an intercrop with trees, maize, and cassava.

Albay, Philippines. A combination of two varieties of Crotolaria is used for improved fallow. Seeds are broadcast in Imperata grasslands. After at least one year, the Crotolaria is slashed and plowed, and annual or permanent crops are planted. 

Strategy: clear Imperata and plant cover crop

Suggest if:

• Farmer wants to plant crop in 3-6 months

• Soil needs OM, N

This is a more intensive strategy for a shorter time period.

1. Clear the site and plant the cover crop, following site preparation and fertilizer recommendations for the species.

2. Maintain the cover crop. Replant where necessary.

3. Kill the cover crop when it is time to plant annual crops.

Strategy: clear planting sites and grow leguminous cover crop over remaining Imperata.

Suggest if:

• Tree crops are to be planted

• No other intercrop is planned

1. Lay out planting areas. Mark 2 m wide strips along the contour, or 1 -2 m diameter cleared circles.

2. Prepare planting areas. Cultivate or spray herbicide and then make furrows in the dead grass.

3. Plant seeds of viny LCCs in the prepared planting areas. Use locally recommended species and P fertilizers.

4. Press. After about 5-8 weeks, the vines reach the Imperata beside the planting area. Press an additional 1 m strip or circle along or around the planting area.

5. Press another 1 m strip or circle every time the vines grow over the pressed Imperata (every 4-6 weeks).

4.3.2 Establishing leguminous cover crops to prevent reinfestation with Imperata

Suggest if:

• Imperata threatens to infest field again

• Farming system is extensive

Leguminous cover crops are most useful as intercrops or relay crops. They shade the soil between rows and occupy the field between cropping seasons, keeping Imperata out.

Protect the food or cash crop from competition with the leguminous cover crop. Choose less aggressive species, or choose species with a short lifespan. Constantly train vines away from trees.

Legume crops that provide food (seeds and pods) are attractive to farmers. They are likely to provide less nitrogen to the soil because nitrogen is concentrated and removed in the seeds.

Species choice for leguminous cover crops to prevent reinfestation of Imperata

Recommended species (see also Appendix C)

• Calopogonium mucunoides

• Canavalia ensiformis (with annuals)

• Canavalia gladiata (with annuals)

• Centrosema pubescens (with tree crops)

• Crotolaria spp. (with annuals)

• Desmodium heterophylla (with tree crops)

• Desmodium intortum (forage)

• Dolichos lablab (food and forage)

• Macrophyllum atropurpureum (forage)

• Mucuina pruriens (not for intercropping)

• Psophocarpus palustris (with tree crops)

• Psophocarpus tetragonolobus

• Pueraria spp. (with tree crops)

• Stylosanthes guyanensis (forage)

• Tephrosia Candida (with tree crops)

• Vigna unquiculata