Food and Cash Crops
Roots and Tubers
Cowpea (Vigna unguiculata (L.) is one of the most ancient human food sources.
Cowpea cultivars have a vining growth habit; however, modern plant breeding has also led to more upright, bush-type cultivars. The vining type is preferred for forage or cover crop use, while the bush type is better suited for direct combining. The extreme variability of the species has led to a number of commercial cultivars grouped by the variance in bean shape, size and color.
Inoculants should be applied on cowpea seeds. Inoculants are marketed in liquid and powder forms for seed inoculation or in granular form for soil inoculation. Powder and granular formulations can consist of clay or peat carriers. Rhizobium inoculant is sensitive to some fungicide seed treatments and fertilisers. Seed-applied inoculant must be applied to the seed just before planting. Large populations of this introduced rhizobia bacteria must survive in the harsh soil environment for 2 to 3 weeks to effectively form nodules on the roots of pulse crop seedlings. In dryland cropping regions, granular inoculant is preferred because it is more reliable in dry seedbed conditions.
Cowpeas vary in growth habit. Erect or semi-erect types with short (<100 days) growth duration are grown mostly for grain. Semi-erect types and trailing plants have longer (>120 days) duration in and are grown primarily for forage. At maturity, leaves dry down but may not drop off completely. Cowpeas need to be harvested when seed moisture content is 14 to18%, depending on the consumer’s requirement. In cowpeas grown for vegetable purposes, the leaves are picked 4 weeks after planting, and this continues until the plants start to flower.
Cowpea can be harvested using a harvester or by hand. The upright cultivars are easy to harvest by machine. Cowpea grown as a dried seed product can be directly combined, using a platform head or a row crop head. Adjustments to combine settings and sieve sizes should be made for the cowpea seed. Because the pods are relatively long, some will touch the ground or be close to it, making it important to run the grain table close to the ground. In the case of cowpeas grown for vegetable purposes, young leaves are mainly picked by hand; older leaves accumulate dust or get spattered with mud from raindrops if not harvested. In most cases, harvesting of cowpea should coincide with the onset of dry season when the dry pods can await harvesting for a week without spoilage. However, to avoid field weathering or shattering, dry pods should not be left in the field longer than 2 weeks after full pod maturity. Harvesting can be carried out manually (hand harvesting) or by using a combine harvester in the case of large-scale production.
Seed quality is important. Care in harvest and post-harvest handling allows to avoid cracked or split seed as such seeds which were allowed to dry on plant are harvested to ensure full maturity. Sorting is done to separate the broken seeds from full seeds.
The leaves are dried to store for the dry season. Usually they are first steamed or boded, but not in all places. Sun-drying requires 1 to 3 days; storage is possible for up to a year because dried cooked leaves are not damaged by insects to the same extent as dried seeds. Excessive losses of P-carotene, vitamin C, and the amino acid lysine often occur in sun-dried leaves; however, these can be reduced by minimal cooking followed by drying in the shade.
The youngest leaves or tender shoots are gathered while in the distinctive green color phase of new growth. Young leaves are tender, usually higher in protein, and, lacking insect damage, often look more appealing. Older leaves accumulate dust or get spattered with mud from raindrops, while younger leaves would not need so much washing.
Buyers want the seeds cleaned and bagged, while others will take the grain in bulk form and clean it themselves. In case of sun drying, package in sacks and put into electrical dryers or spread on a concrete slab in order to reduce the moisture content to about 12%.
Insect pests can devastate cowpea during storage. There are storage insects that cause damage to the seed; it is therefore important to store seed in a protected place. A serious insect pest during storage is the cowpea weevil Callosobruchus maculatus, (Coleoptera: bruchidae). The rising popularity of organic produce lines has created interest in non-chemical disinfestation treatments; as the use of chemicals in controlling these insects is becoming a problem.
The storage life of cowpea depends on its moisture content before storage. The lower the moisture content, the better the quality of seeds in storage. The grain can be stored short term at around 12% moisture or less, with 8 to 9% recommended for long-term storage. Cowpea leaves are dried to store them for the dry season. Sun-dried leaves may store for up to a year because dried, cooked leaves are not damaged as much by insects as dried seeds.