Cowpeas are drought-tolerant and can be produced in areas where very few other crops would survive. Rainfall of 450mm/ year will be sufficient to produce 1t seed/ ha and 4t hay/ha.
The soil can vary from sandy to clay, but easily waterlogged soil should be avoided. They inhibit nitrogen-fixing, a key characteristic of legumes such as cowpeas.
Ideally, the soil should have a depth of at least 1m to ensure sufficient root development to maintain the plant during drought.
The best vegetative growth occurs in temperatures between 21°C and 33°C. Higher temperatures can cause earlier flowering and flower abscission, resulting in poor pod set.
- Cultivars: Indeterminate cultivars such as Bechuana White, Chappy, Encore and Iron Grey are photo-sensitive – flowering is affected by day length and seed yield can be affected by the planting date. Upright and semi-determinate cultivars can be planted throughout the growing season with lower seed loss than in the case of sensitive cultivars. Vegetative growth of both types is not influenced by day length and will therefore continue until the first frost. Generally, a determinate, or bush, type plant produces a full crop all at once and tops off at a specific height; indeterminate cultivars develop into vines that never top off and continue producing until killed by frost.
- Planting: Soil preparation is very important, because it can ensure that fewer weeds emerge soon after planting, therefore reducing competition early in the plant’s life, especially where the availability of water is a problem. Inter-row width depends on the growth habit of the variety being used. Upright types can be planted in 30cm to 90cm rows, semi-runners in 90cm to 150cm rows, and runners in 150cm to 200cm rows, depending on the rainfall. In-row spacing must not be more than 75cm to ensure a good plant population. A planting depth of 5cm is best. Upright types need a plant population of at least 120 000 plants/ha for optimal production and 70 000 plants/ha in the case of semi-runner or runner types.
- Pest control: Cowpeas should be inoculated with Rhizobium bacteria. Any registered chemical can be used to control aphids, while the viral infection they cause can be minimised by planting when aphid populations are not at a peak. To avoid severe nematode infestations, cowpeas should not be grown as a monoculture crop on the same land for more than two seasons.
- Harvesting: Hay is harvested as soon as the first pods start to dry, by hoeing the cowpeas by hand or with a V-blade on a tractor, and then left to dry. Seed is harvested as soon as the pods are dry and harvesting can continue throughout the season.
Source: Directorate Agricultural Information Services, DAFF, in co-operation with the ARC-Grain Crops Institute.