Both cowpea and groundnut can be grown in flat beds or on ridges, depending on the field conditions.
For cowpea, a spacing of 75 cm between the rows and 20 cm between plants within the rows is used for the medium maturing varieties; spacing of 50 cm between the rows and 20 cm between the plants within the row is used for early maturing varieties.
The recommended spacing for groundnut is 75 cm between the rows and 25 cm between the plants within the rows.
For groundnut, planting should be done as soon as possible after the onset of the rains. Early planting is recommended to avoid rosette attack. For cowpea, planting is done when there is sufficient moisture in the soil to allow germination and when there will be enough time for the varieties to mature after the end of the rainy period.
In general, IITA recommends that the ideal time for planting medium maturing varieties is about 60–75 days before the rains are expected to end and for extra-early varieties, about 45–50 days before the end of the rains.
Growing season decisions:
It is important to keep the field for seed production free of weeds from planting to harvesting. All available and effective weed control methods should be used according to growing or field conditions. Mechanical weeding, hand weeding, preemergence and postemergence herbicides can be adopted to keep the fields weed-free.
All the available control methods should be used to reduce disease incidence. Treatment of seeds with chemicals is recommended for both groundnut and cowpea. Fungicides are used to control fungal disease in cowpea. For groundnut, two main diseases are reported in Nigeria: Cercospora leaf spot and rosette during the growing period. Resistant varieties are available for their control.
To ensure good quality and quantity, it is important to control insects in both groundnut and cowpea. Millipedes and termites are the most damaging for groundnut. The most important insect pests of cowpea include aphids, flower thrips, Maruca pod borers, and pod sucking bugs.
Insecticides are recommended to prevent crop losses. In general, the number and the type of insecticide spays will depend on the nature and severity of infestation and also the cowpea variety. However, 3–4 insecticide sprays are recommended for cowpea seed fields.
Rogue off-type plants:
Field inspection is one of the important activities in seed production. Off-type plants are removed from the field as soon as they are seen. Off types have different leaf types, different flower colors, different pod colors, or different maturity periods compared with the variety being multiplied. Not more than 0.5% of off-type plants should be found in a good seed production plot after roguing has been completed. Diseased plants should also be discarded.
Harvesting should timely when most pods are dry. For cowpea, multiple picking may be necessary.
Digging and harvesting for groundnut:
Groundnut is indeterminate in growth habit. Usually, better germination is obtained when seed fields are harvested one week earlier than commercial fields. Optimum harvest dates differ from one variety to another and from one set of growing conditions to another.
Harvesting very early is not recommended. Although immature seeds can grow, their germination is slow, their vigor is low, and their survival can be difficult In stressful growing conditions. Early harvesting can decrease the seed value.
Too late harvesting also has an adverse effect on seed quality (deterioration of the pods, more mechanical damage to the seeds, increased number of seed pathogens). Harvesting is recommended when at least 70% of the seeds are close to or at maturity, i.e., when most of the pods are in the brown and early black stages.
Some environmental elements can influence seed quality during harvesting because of high moisture content (35–60%). High temperatures will cause physiological heat damage that will reduce germination and vigor. A good rule of thumb is to harvest groundnut as soon as possible after seed moisture has reached 20 to 25%.
Threshing and decorticating can be done by hand or by using a hand-operated decorticating machine. Care should be taken to prevent cracking the kernels. For cowpea, it is possible to identify off-type seeds (different seed coat colors, different seed sizes).
Big seeds versus small seeds:
In general, many farmers and seed producers think the bigger the seeds, the better the seed quality. Others believe that smaller seeds germinate faster and are therefore better than larger seeds. Although this is true, it does not mean that larger seeds are poor quality but they take more time to hydrate and germinate. Small seed size is usually associated with immaturity. This is not always true, as some larger seed sizes can be immature.
Postharvest handling of seeds (curing)
Groundnut should be cleaned before being dried. Cleaning and spreading of seeds will reduce drying time and costs. Seeds can be damaged by excessive drying, rapid drying, or drying at high temperatures. For cowpea, the moisture content should not be more than 10%.
Groundnut seeds should be stored in a cool, dry, airy environment. They can be shelled soon after harvest and stored in bulk containers. Continuous airflow should be ensured. Cowpea seeds should be properly stored to avoid attack by bruchids. Seeds should be stored using fumigants in closed containers or in closed rooms.
The production of high quality groundnut and cowpea seeds necessitates a high level of management that covers the period from planting to the delivery of seeds to the growers. Seed growers should plan all farm operations well in advance to ensure the seed crop has the highest priority. Lastly, agronomic practices (disease management and maturity at harvest) should be applied properly in seed fields.
H.A. Ajeigbe, T. Abdoulaye, and D. Chikoye