Cowpeas are leguminous crops that can be used to provide vegetable and grain for food. The crop can withstand drought, short growing period and its multi-purpose use makes it an attractive alternative for farmers in marginal, drought-prone areas with low rainfall. It is suitable for a variety of intercropping system.
Cowpea farming in Kenya is done for the cowpeas seeds and also their leaves. The cowpeas are the easiest of the plants in the bean family to grow. They do well in the harshest of climates and require very little rainfall. Cowpeas are rarely grown under irrigation since they yield a lot of leaves when exposed to a lot of water but produce little grain. The rainfall required for the farming of cowpeas is about 200mm in the season of growth.
Worth noting is that cowpeas are indigenous to Africa having been in the continent over 3000 years ago.
The cowpeas leaves are a good source of Vitamins A, B and C and are rich in calcium, phosphorus, carbohydrates proteins and fiber. Dried seeds contain protein and carbohydrates. Cowpeas are recommended for consumption, by health experts due to the health benefits.
In some areas cowpeas is grown for pasture, hay, silage as a cover crop and green manure.
Utilization: Cowpea can be used at all stages of growth as a vegetable crop. The tender green leaves and immature pods are used as vegetable. Green cowpea seeds are boiled, canned or frozen. Dry mature seeds are also suitable for boiling and canning.
Potential Production
The production of cowpea as a leafy vegetable has markedly increased in Kenya as farmers shift to more drought tolerant vegetable crops. Cowpea leaves are mainly sold in the local market and super markets.
Varieties
The growth habits vary from spreading, semi spreading to upright.
Improved Varieties
1. Dual Purpose (leaves and grains for food):
- Kitui black eye
- M66 (tolerant to cowpea yellow mosaic virus and scab),
- Katumani 80 (resistant to aphids; moderately tolerant to thrips, pod borers and leaf hoppers but susceptible to CYMV)
- Kunde 1
- Ken Kunde 3
- KVU 27-1
2. Grain for food
- Zebra, Randa
- KVU-419- grain for food tolerant to cold and recovers very fast from drought
3. Vegetable type
- KVU HB tolerant to virus diseases
- KCP 022 Drought tolerant
- MTW 63″, ICV Pest tolerant
- Ngombe good for green leaf production, sweet taste of grain
- Local varieties- Varying seed colours and most are dual purpose
Ecological requirements
Altitude
Production altitude varies from sea level to below 2000m above sea level depending on the variety.
Rainfall
Cowpeas can grow under rainfall ranging from 400 to 700 mm per year. The plants have a great tolerance to water logging. Well-distributed rainfall is important for normal growth and development of cowpeas.
Temperature
Cowpeas grow best in warm conditions. The optimum temperature for growth and development is around 20-35 °C. The crop is not tolerant to cold soils.
Soils
Cowpeas are grown on a wide range of soils but the crop shows a preference for sandy soils, which tend to be less restrictive on root growth. It is more tolerant to infertile and acid soils than many other crops. Cowpea can grow in a pH range of 5.6 to 6.5.
Planning for production
- Select suitable site with required production requirements
- Choice of variety depends on agro-ecological zone. Some improved varieties are suitable for the dry areas. Drought tolerant varieties include Katumani 80, kitui black eye, M66, KCP 022. Other factors are maturity period, resistance to diseases and pests and general market preference.
- For grain production, colour and size of seeds are important to consumers
Propagation
Cowpea is directly grown from seed. Depending on the purpose for production, it can ether be grown as a sole crop or intercrop with cereals such as maize, sorghum or pearl millet. Production is mainly rainfed, however with irrigation is also used for commercial production.
Land Preparation
Land should be ploughed and harrowed. Then ridged or left as flat seedbeds after harrowing.
Planting
Planting should be done at the onset of rains for rainfed cultivation. The spacing varies depending on the production system. When produced as a green vegetable, they are commonly grown as a monocrop in rows 30 to 40 cm apart with 8 to 12 cm between plants or 60 between the rows and 20-30 cm between plants. Planting depth is 2.5-5 cm depending on the environmental condition. Deeper planting is recommended the drier areas.
Note: Local seeds variety should be treated with a fungicide before planting.
Intercropping
Cowpeas are seed planted about 20 to 40 cm apart as an intercrop with pearl millet, sorghum or maize at wide spacing. Cowpea serves as a security crop in case of failure of the main crops.
They improve soil fertility when grown in rotation with other crops such as cereals
Fertilizer
Fertilizer application in cowpea production depends on soil fertility. As a legume, it does not require a high rate of nitrogen fertilization because its roots have nodules in which soil bacteria called Rhizobia help to fix nitrogen from the air. Seed can be inoculated with the appropriate Rhizobium species for optimum nitrogen fixation; however nodules will generally form on cowpeas. Where soils are highly eroded an application of dry compost or manure is beneficial.
Weeding
Weeding is important during the early stages of the crop; later the crop covers the ground and suppresses weeds. The first weeding should start two weeks after emergence and the second weeding just before flowering.
Diseases
Fungal diseases – Leaf spot, Scab Powdery mildew
Viral Diseases – The most common virus disease on cowpeas is cowpea aphid-borne mosaic potyvirus. It is transmitted by aphids. They cause irregular light and dark green mosaic patterns on the leaves. Plants may be stunted and fail to produce normal pods.
Pests – African bollworm Flower thrips Pollen and blister beetle, Pod sucking Bugs
Control
- Plant resistant varieties.
- Use healthy, disease-free seeds rather than saving seed from a crop that could be infected.
- Practice crop rotation with non-legumes (e.g. cereals).
- Remove alternative hosts of virus diseases (legumes).
- Timely control of weeds
- Use recommended fungicides and insecticides to pests
Harvesting
Systems commonly used in harvesting of cowpea as a leafy vegetable include;
- Uprooting the entire plant at the 3-5 true leaf stage before the leaves become too mature and fibrous or dual-purpose production where sequential leaf harvests are made during the vegetative phase of plant growth, followed by seed production at the end of the season.
- Harvesting cowpea at 7-days interval give higher leaf vegetable yields but higher grain yields are obtained when no leaf harvesting is done to the crop at its vegetative phase.
- For dual-purpose production, sequential leaf harvests are made during the vegetative stage of the crop followed by seed harvesting at the end of the season. This system predominates with most subsistence growers who practice intercropping.
- Pods should be harvested when the pods have turned brown. Pods are threshed, dried and storage dust used to protect the seeds from storage pests such as weevils.
- For the cowpea seed market, quality of seed is important, so care during harvesting and post-harvest handling is important to avoid cracked or split seed.
Post harvest management
The leaves may be dried and stored for later use.
Challenges in production
- The glut of cowpea leaves in the market can lead to low price and post-harvest losses especially during the rainy season. The leaves are also highly perishable hence should be sold immediately after harvesting.
- Growers tend to recycling seeds during production resulting in seed born disease such as scab, bean rust and Leaf spot. Use of certified seed and varieties resistant to diseases and pests is recommended.
Advice to potential growers
Growers are advised to identify their markets as early as possible, rather than waiting until after harvest. The value of the cowpeas leaves vary with harvesting stages with the tender young leaves fetching a better price than the more fibrous mature leaves. For commercial production growers should plan well for production ensuring a good supply of the vegetables during the dry season when the demand is high.
Consistency in supply ensures that the market segment is maintained. This can be achieved by planting early maturing varieties and use of irrigation.
Post harvested losses can also be minimized by drying and storing the cowpea leaves.