Soil improver
An N-fixing legume, cowpea can be included in crop rotations to increase soil nitrogen. Cowpea is particularly useful for building up fertility in soils that have been run down from overcropping. When the crop is fully nodulated, cowpea can fix 20 to 140 kg residual N/ha into the soil. This gives a significant bonus to later cereal crops in the rotation (Mullen, 1999). Cowpea forage helps to eliminate the need for a fallow period between a sorghum crop and the following wheat crop, while providing cover to the soil during summer without demanding too much water (Ledbetter, 2005).
As a cover crop, cowpea can be incorporated into the soil at any time when sufficient green material is available, but this is best done at peak flowering (Cameron, 2003). Cowpea forage has a relatively low C:N ratio and N is quickly mineralized. It is thus a valuable green manure where it is intended to provide readily available, biologically-fixed N for subsequent crops (Creamer et al., 1999).
Weed and disease cycle breaker
Cowpea should be sown in rotation with a grass crop to minimize weed and disease build-up (Mullen, 1999).