Cowpea (Vigna unguiculata) is a versatile legume grown for human consumption as well as for soil improvement and animal fodder. It is the second most-planted grain legume in Africa (National Research Council, 2006). Though cultivated throughout the tropics, and thus familiar to smallholder farmers, there are almost certainly varieties that farmers in a given area are not aware of that could improve the resilience and productivity of their fields.
Background and benefits
Most cowpea types cultivated by small scale farmers in the tropics have been either early-maturing varieties grown as a pulse (dry beans) or late-maturing varieties grown mostly for their vines that are cut and used for animal fodder. Some Nigerian farmers have increased their annual income by 25% through the sale of cowpea fodder during the peak of the dry season (Dugie et al., 2009), when livestock have little to graze. Recent years have seen a research emphasis— by the International Institute of Tropical Agriculture (IITA), for example—on dualpurpose varieties with increased production of both grain and vegetative biomass.
Dual-purpose varieties typically have a more spreading or semi-erect growth habit than the erect, bush-type varieties selected for mechanical harvest. As mentioned above, the increased biomass is useful for animal fodder. The extensive vine growth of a good creeping-type variety can also play a key role as a green manure, as long as at least some of the biomass is left in the field. Keeping soils covered is especially important in the tropics, where soils are subjected to intense heat from the sun.
ECHO research in South Africa has demonstrated the beneficial impact of a long-vined cowpea variety on soil fertility. By 6 months after seeding, with no fertility inputs and <700 mm rainfall on a soil with 87% sand, a low-growing cowpea variety (IT98D-1399) from AVRDC/ICRISAT-Niger produced 3.4 t/ha of dry, above-ground biomass when planted at a 50 X 50 cm spacing. That amount of biomass contained 90 kg/ha of nitrogen. When vines were left on the soil surface, soil nitrate concentration—six months after seeding cowpea—increased from 7-8 parts per million (ppm) in bare ground and weedyfallow plots to 14 ppm with cowpea.
Where cowpea grows best
A warm season (25-35 °C) crop, cowpea is adapted to a wide range of soil and moisture conditions. For maximum biomass production (or forage and/or soil cover), rainfall amounts of 750-1100 mm are optimal (Tropical Forages); 500 mm or less is sufficient for early-maturing varieties (Dugie et al., 2009). Although tolerant of poor, sandy soils, cowpea grows best in well-drained sandy loam to clay loam soils with a pH of 6 to 7. It does not tolerate frost or overly wet (waterlogged, poorly drained) soil.
How to obtain cowpea seeds
Look for cowpea varieties in the country in which you are working. Other institutions may already be working with one or more improved IITA varieties (website: www. iita.org). Also, be on the lookout for local varieties with multi-purpose traits.
Alternatively, seeds are available from ECHO’s Florida-based seed bank, which recently acquired the following cowpea varieties
Samoeng: Short creeping vine; intercropped with upland rice; plump pod, black seed.
Mavuno: Creeping cowpea reported by Joel Wildasin (former ECHO intern and staff member) as a best local variety from Magu, Tanzania. ‘Mavuno’ means ‘harvest’ in Swahili. Large cream-colored seeds, large leaves and long, big pods.
In reference to the ‘Samoeng’ variety fromThailand, Rick Burnette, who now heads up the ECHO Agriculture Department in Florida, had this to say about creeping cowpea varieties:
“In the uplands of Southeast Asia, creeping cowpea varieties are typically grown in association with the main crop of upland rice, along with other secondary crops such as cucurbits. All of these are established at the same time at the beginning of the rainy season. In such situations, creeping cowpea germinates and becomes established while the rice crop is still small, while there is more exposure to sunlight. However, such types of cowpea can tolerate much less sunlight when other crops, especially upland rice, grow taller. As creeping cowpea does not climb, the other crops in the stand are not in danger of being overcome by the viney, prostrate legume. As a result, creeping cowpea increases crop diversity in upland rice fields, offering green pods as a vegetable in the middle of the rainy season. The legume also fixes nitrogen and provides a degree of weed control in the understory of the rice crop.”
Both of these new varieties have grown well on ECHO’s sandy soils at our demonstration farm in Florida. Those registered with ECHO Community as agriculture development workers may request a complimentary trial packet of one or several of the cowpea varieties from the ECHO Florida seed bank. Visit ECHOcommunity.org for information on how to register. We encourage you to grow these alongside your local varieties and compare the growth and production of the plants.
Clear the ground of weeds before planting. Planting should be timed to allow enough time during the rainy season for the crop to mature. Plant three seeds per planting station, thinning to two plants per station at two weeks after planting (Dugie et al., 2009). Use a wider spacing for prostrate varieties than for bush-type varieties. For spreading varieties, plants should be established 75 cm apart between rows and 25-50 cm apart within rows. Depending on the variety, dry beans will be ready for harvest at 90 days (early-yielding varieties) to 210-240 days (varieties that typically flower later in the season when day length shortens) after seeding (Tropical Forages). See references below for more detailed information.
References and Further Reading
Tropical Forages fact sheet: www.tropicalforages. info/key/Forages/Media/Html/ Vigna_unguiculata.htm
CGIAR fact sheet (with information on the economic impact of grain/fodder cowpea): http://www.cgiar.org/our-research/crop-factsheets/cowpea/
Dugje, I.Y., L.O. Omoigui, F Ekeleme, A.Y Kamara, and H. Ajeigbe. 2009. Farmers’ Guide to Cowpea Production in West Africa. IITA, Ibadan, Nigeria. 20 pages. www.icrisat.org/tropicallegumesII/pdfs/ Cowpea.pdf
National Research Council. Lost Crops of Africa: Volume II: Vegetables. Washington, DC: The National Academies Press, 2006.