Cowpea is really a key crop in the dry (arid) regions of central, south and western Africa, extending from the northern areas of South Africa through the Savannah and into the Sahel zone. It does well in the tropics and subtropics and is part of the diet of millions of African people. It is also an excellent feed for animals.
AN AFRICAN CROP WITH DIVERSITY
According to the National Academies Press publication The Lost Crops of Africa the cowpea has the ability to help lift Africa’s food quality in the 21st century. “The species is rich in useful genetic diversity. It produces several different tasty foods. The plant is deep rooted, vigorous in growth, and reliable in production. It is both drought-tolerant and adapted to poor soils.
“The seeds are exceptionally nutritious, possessing protein (up to 24 percent in dry seeds) and a trove of other essential nutrients. As a dietary component, it complements the otherwise unbalanced diets the poorest sectors are forced to stomach.
“And, perhaps because of its African birth it beats out other legumes for performance on a variety of soils and an adversity of conditions found across this multiform continent. Indeed, cowpea has been called “a nearly perfect match for the African soil, weather, and people”.
According to this paper, “the crop originated as an inconspicuous little creeper among the rocks of the dusty southern Sahel and the bone-dry upper rim of central Africa. Africans living there thousands of years ago saved the best seeds.”
GROWTH AND PHYSIOLOGY
Cowpea has various growth forms ranging from erect and bushy to trailing and climbing vines. It is often used as a cover crop in conservation tillage and one sees it more and more grown as animal feed. The strong taproot has spreading lateral roots in the upper surface soil layers, an adaptation for dry conditions.
The dark green leaves are arranged in trifoliate (three-leaf) whorls, and the leaf shape varies from lance-like to oval, with a leaf stem that can be from 5cm to 25cm long. The flowers come off the floral axis (stem) in opposite and alternate patterns (this is called a raceme). In the case of cowpea there are usually only two or a few flowers per inflorescence.
Flowers are noticeable with white petals, and white, yellow, pink, pale blue or purple centres. According to the Agricultural Research Council (ARC) of South Africa, seeds come in a multitude of shapes, colours and sizes and the number of seeds in a pod can be from 8 to 20. The outer cover of the seed can be smooth, wrinkled, white, brown, green, buff, speckled, blotched, eyed or mottled. Pods may be erect, crescent-shaped or coiled, yellow when ripe but also brown or purple.
These differences are signs of healthy diversity in the species. Diversity is the key to survival, especially for farmers who farm in tough, even harsh, African conditions. Maize farmer, Michris Janse van Rensburg, from the Free State in South Africa, says his cowpea crop did well for him this last season, which has been part of a cycle of the worst drought in recorded history.
THE COWPEA LIKES IT HOT
Germination can happen at 8.5°C but no lower, and a good temperature for leaf growth is 20°C. ARC researchers say Cowpea likes the heat and tolerates drought which Michris’ pictures certainly prove. The optimum temperature for growth and development is around 30 °C.
Seed Co, a seed distributor in Zimbabwe, describes cowpea as a day-length sensitive crop that flowers into shortening days. “Planting in spring will yield a large quantity of fodder at the expense of pods and grain, while sowing with normal summer planting rains optimises grain production. Late summer plantings are generally not successful, since reproductive growth commences while plants are still in the seeding stage.”
As a legume, the cowpea fixes its own nitrogen. Too much fertiliser will push leafy growth and reduce grain production. Plants have an extraordinary capacity to survive and often respond well to a bit of a threat, to produce what growers need. Putting down too much fertiliser increases leafy, vegetative growth at the expense of grain production.
Seed Co reports that inoculation of seed is not necessary. The cowpea has root node bacteria (Bradyrhizobium spp) that create the right environment for the plant to tolerate hot conditions in areas where cropping is difficult. It is more drought-tolerant than many other crops and can grow where the annual rain is between 400mm and 700 mm.
Timing is critical and cowpeas need rain particularly at flowering and podding. Rainfall extremes, too much or way too little, can be problematic for this crop.
In times of serious drought and very low soil moisture, the cowpea plants changes their leaf orientation and close the stomata to reduce heat stress. Flowers and pods separate from the main stem if there is a need to reduce growth and conserve resources.
Seed Co recommends a plant population of between 100 000 and 150 000 plants per hectare; a row width of between 45cm and 75cm, and plant spacing in the row between 10cm and 20cm. The seed rate is between 20kg and 40kg per hectare depending on seed size. The best times to plant are December and January. Sowing early will lead to reduced yields.
Cowpeas prefer sandy, well-drained soils which favour expansive root growth and tolerates infertile and leached soils. Soil pH of between 5,6 and 6,0 is ideal.
Resources: The Agricultural Research Council of South Africa, Production Guidelines for Cowpea; Seed Co, a producer of certified crop seed in southern Africa.
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