Rural Industries Research & Development Corporation

The New Rural Industries
A handbook for Farmers and Investors

Cowpea

Introduction

Cowpea (Vigna unguiculata (L.) Walp.) is a highly variable annual legume species that originated in Africa. There are three recognised subspecific groups of cultivated cowpeas. Two of these are grown in Australia with most varieties grown for grain, forage and green manure being in the `cowpea' group. The other type, the yardlong bean, is a minor vegetable.

Cowpeas vary in growth habit from erect or semi-erect types with short (<100 days) growth duration grown mostly for grain, to longer (>120 days) duration semi-erect to trailing plants grown primarily for forage. Cowpea is a minor crop in Australia, its main advantage being drought tolerance.

Cowpeas are grown as a green manure crop in coastal sugarcane areas, as a forage or dual purpose grain/forage crop in coastal and subcoastal southern Queensland, and as a grain crop from central Queensland to central NSW. Grain production is shown in Table 1- (not available in this html version) - the most recent published statistics).

Worldwide production exceeds 2 million tonnes but only a small proportion enters international trade. The major production areas are Africa (Nigeria, Niger), Asia (India, Myanmar) and the Americas (USA, Brazil, West Indies). Of the developed countries, only the USA is a substantial producer and exporter. The predominant grain type traded is the `blackeye pea', a large white seed with a black patch around the hilum, although markets exist for seed with a range of sizes and colours. Small red-seeded cowpeas are sometimes substituted for adzuki beans in Japan.

Production requirements

Cowpeas are grown on a wide range of soils but show a preference for sandy soils which are less restrictive of root growth. This adaptation to lighter soils is coupled with tolerance of drought through reduced leaf growth, reduced water loss through stomates, and leaf movement to reduce light and heat load when stressed. Conversely, cowpea has poor tolerance of waterlogging.

Cowpeas grow during summer. The base temperature for germination is 8.5^oC and for leaf expansion is 20^oC. The optimum temperature for growth and development is around 30^oC.

Varieties vary in their response to day length, some being insensitive and flowering in 30 days after sowing when grown at a temperature around 30^oC. Time of flowering of photosensitive varieties is dependent on time and location of sowing and may be more than 100 days. Even in early flowering varieties, the flowering period can be extended by warm and moist conditions, leading to asynchronous maturity. The optimum sowing times are December in NSW and January in Queensland. Early-sown crops tend to have elongated internodes, are less erect, more vegetative and lower yielding than those sown at the optimum time.

Crop agronomy

Varieties selected for grain production in Australia are the more erect, short duration plant type (Table 2 - not available in this html version). Later maturing varieties such as Arafura, Ebony PR and Meringa are available for forage production.

For grain production, growers generally aim for a plant population of 200,000 to 300,000/ha requiring a seeding rate of about 60 kg/ha for Banjo, 50 kg/ha for Big Buff and 25 kg/ha for Red Caloona. Narrower rows (30-50 cm) are preferred to wider rows (70-100 cm), although the latter may be necessary in minimum-till farming systems.

Cowpeas are usually grown dryland rather than irrigated and fertiliser application depends on anticipated yield and soil fertility. As cowpea is a legume, it is not necessary to apply nitrogen but application of a phosphatic fertiliser at a rate of up to 20 kg P/ha is usually beneficial.

Annual grasses and some broadleaf weeds can be controlled by a presowing application of trifluralin which is the only herbicide registered for use on cowpea.

Cowpea is very attractive to insects, particularly flower thrips, pod borers such as Heliothis, and sucking bugs such as green vegetable bug. Control by one or two applications of insecticide is invariably necessary. Failure to control insect pests could result in grain being downgraded from food quality to stockfeed and make production uneconomic. Bruchids may infest stored grain in subtropical and tropical regions.

The most important disease of cowpea is stem rot caused by Phytophthora vignae. This disease is common in the wetter coastal and subcoastal areas, and on heavier soils which may become waterlogged. Red Caloona, Ebony PR and Holstein have resistance to the most prevalent races of the pathogen at the time of writing but resistance might be expected to break down in the future.

Harvest and marketing

Cowpeas are direct harvested and header settings are critical to produce undamaged seed because cowpea seeds are large and easily split. They need to be harvested when seed moisture content is 14-16% using a low drum speed and open concave on the header.

Most crops are traded by members of the National Agricultural Commodities Marketing Association which has established standards for grain quality. Varieties Big Buff and Holstein are proprietary varieties protected by PBR and can be grown only under contract to the seed company licensee.

Economics

Costs of production are similar to those for mung bean. Returns are dependent on seed quality, being around $800 /t for food grade but dropping to $250/t or less for stockfeed. This dichotomy in pricing makes cowpeas more risky for growers than mung beans, the summer pulse alternative.

Key contacts

Key References

Singh, S.R. and Rachie, K.O. (Eds) 1985. `Cowpea Research, Production and Utilization'. John Wiley and Sons, Chichester, U.K.

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