The cowpea, Vignaunguiculata, is an annual herbaceous legume from the genus Vigna. Due to its tolerance for sandy soil and low rainfall it is an important crop in the semi-arid regions across Africa and other countries
Most cowpeas are grown on the African continent, particularly in Nigeria and Niger which account for 66% of world cowpea production.The Sahel region also contains other major producers such as Burkina Faso, Ghana, Senegal and Mali. Niger is the main exporter of cowpeas and Nigeria the main importer. Exact figures for cowpea production are hard to come up with as it is not a major export crop. A 1997 estimate suggests that cowpeas are cultivated on 12.5 million hectares (31 million acres) and have a worldwide production of 3 million tonnes. While they play a key role in subsistence farming and livestock fodder, the cowpea is also seen as a major cash crop by Central and West African farmers, with an estimated 200 million people consuming cowpea on a daily basis.
According to the Food and Agriculture Organisation of the United Nations, as of 2012, the average cowpea yield in Western Africa was an estimated 483 kilograms per hectare (0.195 t/acre), which is still 50% below the estimated potential production yield. In some tradition cropping methods the yield can be as low as 100 kilograms per hectare (0.040 t/acre).
Outside Africa, the major production areas are Asia, Central America, and South America. Brazil is the world’s second-leading producer of cowpea seed, accounting for 17% of annual cowpea production, although most is consumed within the country.
Cowpeas thrive in poor dry conditions, growing well in soils up to 85% sand. This makes them a particularly important crop in arid, semi-desert regions where not many other crops will grow. As well as an important source of food for humans in poor arid regions the crop can also be used as feed for livestock. Its nitrogen fixing ability means that as well as functioning as a sole-crop, the cowpea can be effectively intercropped with sorghum, millet, maize, cassava or cotton.
The optimum temperature for cowpea growth is 30 °C (86 °F), making it only available as a summer crop for most of the world. It grows best in regions with an annual rainfall of between 400–700 millimetres (16–28 in). The ideal soils are sandy and it has better tolerance for infertile and acid soil than most other crops. Generally 133,000 seeds are planted per hectare (54,000/acre) for the erect varieties and 60,000 per hectare (24,000/acre) for the climbing and trailing varieties. The grain can be harvested after about 100 days or the whole plant used as forage after approximately 120 days. Leaves can be picked from 4 weeks after planting.
These characteristics, along with its low fertilisation requirements, make the cowpea an ideal crop for resource poor farmers living in the Sahel region of West Africa. Early maturing varieties of the crop can thrive in the semi-arid climate, where rainfall is often less than 500 millimetres (20 in). The timing of planting is crucial as the plant must mature during the seasonal rains. The crop is mostly intercroped with pearl millet and plants are selected that provide both grain and fodder value instead of the more specialised varieties.
Storage of the grains can be problematic in Africa due to potential infestation by post-harvest pests. Traditional methods of protecting stored grain include using the insecticidal properties of Neem extracts, mixing the grain with ash or sand, using vegetable oils, combining ash and oil into a soap solution or treating the cowpea pods with smoke or heat.More modern methods include storage in airtight containers, using gamma irradiation, or heating or freezing the grain. Temperatures of 60 °C (140 °F) kill the weevil larvae, leading to a recent push to develop cheap forms of solar heating that can be used to treat stored grain. One of the more recent developments is the use a cheap reusable double bagging system (called PICs) that asphyxiates the cowpea weevils.