The cowpea (Vigna unguiculata L. Walp) is one of the most important seed legumes in Africa. The edible leaves and seed have significantly high levels of protein (up to 40%), as well as trace elements, and it has the potential to overcome protein-calorie malnutrition and trace element deficiency in rural communities. It is also a nitrogen-fixer for soil.
Millions of people in Africa suffer from protein-calorie malnutrition and micronutrient deficiency. Hunger is a result of food insecurity due to low crop yields, which stem from low rainfall, nutrient-poor soils, and unimproved crop varieties, as well as the effects of insect pests and diseases.
Although nitrogen fertilisers can largely overcome foil infertility and increase crop yields, they are expensive and largely inaccessible in parts of Africa. While the consumption of meat, dairy products and seafood can overcome these deficiencies, they are equally expensive and therefore unavailable for most rural African households.
The cowpea is actually not a pea, but rather a bean. It is commonly known as the black-eyed bean, and in Afrikaans as akkerboon or dopboontjie, among other names.
Origins
Cowpea is one of the most ancient human food sources and has probably been used as a crop plant since Neolithic times, the last stage of the Stone Age, when the early people started living in villages, grow food and keep animals. The lack of archaeological evidence has given rise to contradicting views on whether the cowpea originated from Africa, Asia, or South America.
Some literature says the cowpea, along with sorghum and millet, was introduced to the Indian subcontinent about 2 000 to 3 500 years ago, while others say cowpeas reached Europe and maybe North Africa before 300 BC from Asia.
Cowpea is now grown throughout the tropics and sub-tropics and has become a part of the diet of about 110 million people.
Some researchers believe that it originated in the northern part of South Africa and was the centre of speciation of V.unguiculata because of the presence of the most primitive wild varieties species. It is believed that it spread from there to Mozambique and Tanzania, where the subspecies V.pubescens evolved.
Others believe it originated from West Africa because it grows wild and is cultivated in that region. Today West and Central Africa is the leading cowpea producing regions in the world and produce more than two thirds of the estimated three million tonnes of cowpea seed annually.
At present, Nigeria is the world’s leading cowpea producing country, followed by Brazil. Other African countries, including Senegal, Ghana, Mali, Burkina Faso, Niger, and Cameroon are significant producers. Elsewhere in the world, India and Myanmar in Asia, the West Indies and the USA are also big producers.
Different cowpea cultivars are grouped and named by the shape, size, and colour of the bean or pod.
Nutritional value
The whole plant is edible, including the roots, green leaves, immature pods, and green seeds, as well as mature pods and seeds.
It is rich in fibre, protein, iron, potassium, and amino acids, while it is low in fat and calories, as well as folate, which lowers the chances of birth defects and helps women have a healthy pregnancy.
Uses for cowpeas:
- The leaves and growth points are used as a vegetable dish. Dried leaves can be used as a meat substitute.
- The green seeds are sometimes roasted like peanuts and used as a substitute for coffee. Ground, dried seeds mixed with onions and spices can be fried in oil, or the seeds can also be cooked.
- The plant can be used as green manure and it can be planted for hay production. Silage can be made by mixing the green leaves with sorghum or maize.
Cultivation
The extreme variability of the species has led to several commercial cultivars grouped and named by the shape, size, and colour of the bean or pod.
Cowpeas are drought resistant and heat-loving, and grow best during summer. The best temperature for germination is 8,5 °C, and for leaf growth 20 °C. The optimum temperature for growth and development is around 30 °C.
The different varieties respond differently to day length, with some being sensitive and start flowering within 30 days after sowing, while others may take up to 100 days. Even in early flowering varieties, the flowering period can be extended by warm and moist conditions, which results in them not maturing at the same time.
In Southern Africa, the optimum sowing time is from December to January. Crops sown early have longer stems between nodes, are less erect, have denser leave growth and a lower yield than when sown at the optimum time.
The presence of nodular bacteria specific to cowpea (Bradyrhizobium spp.), which help the plant absorb nitrogen, make it suitable for cultivation in the hot, marginal cropping areas of Southern Africa, as well as in the cooler, higher rainfall areas. However, cowpeas are much less tolerant to cold soils.
Cowpea is more drought-tolerant than groundnuts, soya beans, and sunflowers as it utilises soil moisture more efficiently.
It grows well when rainfall is between 400 to 750 mm per annum and well-distributed rainfall is important. Adequate watering is especially important during the flowering and podding stage.
Cowpeas react to serious moisture stress by limiting leaf growth and by reducing leaf area exposed to the sun by turning leaves away and closing the stomata. It also throws off flowers and pods during severe moisture stress to restrict growth.
Soil
Although cowpeas are more tolerant to poor, acidic soil and can be grown in a wide range of soils, it shows preference to well-drained sandy soils with a pH of between 5,6 and 6,0.
Contact details
Jurie van der Walt at jurievdw@mweb.co.za. His books are freely available on request. The history of food and why we eat it (2020), and We need to revive the ancient indigenous food crops of Africa (2021)
Additional reference
Dakora, F.D., Belane, A.K. (2019) Evaluation of Protein and Micronutrient Levels in Edible Cowpea (Vigna Unguiculata L. Walp.) Leaves and Seeds. Frontiers in Sustainable Food Systems Crop Biology and Sustainability
https://doi.org/10.3389/fsufs.2019.00070
https://www.frontiersin.org/articles/10.3389/fsufs.2019.00070/full
