Vigna unguiculata (L.) Walp.

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Leguminosae

Synonyms

Vigna sinensis (L.) Savi; Vigna sinensis Endl.; Vigna catjang (Burm.) Walp. There is a difference of opinion regarding the valid name for this plant. Verdcourt of the Royal Botanical Gardens, Kew (personal communication), prefers V. unguiculata, with the several cowpeas throughout the world as cultivars.
Barnard (1969) has divided this variable species into three main groups:

  • Var. sinensis: 

the common cultivated cowpea, with medium length, pendant pods, and medium-sized, kidney-shaped or roundish seeds;

  • Var. sesquipedalis: 

the yard long or asparagus bean, which has long pendant pods which are inflated when green and shrivel when ripe, with elongate, kidney-shaped seeds; and

  • Var. cylindrica or catjang (Vigna catjang [Burm.] Walp.): 

which has short, erect pods and small oblong or cylindrical seeds.

Common names

Cowpea, occasionally southern pea (United States).

Description

Herbaceous annual with twining stems varying in erectness and bushiness. Leaves trifoliate, petioles 2.5 to 12.5 cm long. Central leaflet hastate, 2.5 to 12 cm long, smooth, lateral leaflets irregular. Flowers in axillary racemes on stalks 15 to 30 cm long. Pod pendulous, smooth, 10 to 23 cm long with a thick decurved beak and 10- to 15-seeded. Seeds 4 to 8 mm long, 3 to 4 mm broad, variable in size and colour (Barnard, 1969).

Distribution

The country of origin is uncertain. Vavilov (1951) thought it might be India, with secondary centres in China and Ethiopia. Recent workers believe it to be of central African origin. It is widespread throughout the tropics and most subtropical areas.

Season of growth

Summer-growing.

Altitude range

Usually a low-altitude plant, but will grow quite well up to 1 500 m elevation.

Rainfall requirements

For forage purposes, a rainfall of 750 to 1 100 mm is preferable. It will tolerate lower rainfall, but in high rainfall areas disease and insect attacks increase.

Soil requirements

It is tolerant of a wide range of soil textures from sands to heavy, well-drained clays. Heavy clays tend to encourage vegetative growth at the expense of seed production. It adapts to a wide range of pH, but prefers slightly acid to slightly alkaline soils. It has little tolerance of salinity (Johnson, 1970).

Rhizobium relationships

The cowpea is nonspecific but inoculation with a selected cowpea strain of inoculum is an advantage. It nodulates freely with native rhizobia. Johnson (1970) found that 45 kg./ha nitrogen depressed nodulation. Nodulation is also affected by high soil temperatures hut deep planting helps overcome this defect (Philpotts, 1967).

Ability to spread naturally

Does not spread in unprepared land.

Land preparation for establishment

Performs best if treated as a crop sown on a well-prepared seed bed; will, however. establish quite well on a roughly prepared seed bed from an initial ploughing or disc harrowing. The large seed helps in establishment.

Sowing methods

Cowpeas may be sown broadcast on rough seed beds or be drilled into well-prepared ground in rows 50 to 75 cm apart. Maize planters with cowpea plates are usually used. Can be sod-seeded into pastures, provided soil disturbance is adequate and the crop is fertilized. It is often sown in maize crops at the time of the last interrow cultivation. Seed is sown at from >.5 to 7.5 cm, the latter being preferable, from spring to mid-summer where frosts are likely; it is sown later in frost-free areas. Early sowings give higher yields (Hendricksen, 1969). Sow 17 to 39 kg./ha drilled or 45 to 95 kg./ha broadcast.

Number of seeds per kg.

4 180 to 8 800. Ezedinma (1965) found that seed size did not affect performance. The percentage of hard seeds is low. Seed will remain viable for up to three years if stored in a cool dry place, but normally seed from the last harvest should be used for the next planting.

Seed treatment before planting

Usually no preparation needed to break dormancy. Inoculation is not necessary as the cowpea is nonspecific. Pelleting is not needed. For insect and disease control, treat with thiram (1:200 by weight) and with aldrin to control bean fly before planting (Johnson, 1970).

Nutrient requirements

Cowpea grows well without fertilizer in the better soils. In soils of low fertility, it responds to phosphorus and potash and often some nitrogen. Up to 10 kg./ha of nitrogen and 40 to 70 kg./ha P2O5 and K2O may be needed in low fertility soils (Johnson, 1970). There is a response to calcium where the pH is low but this may be a response to the released molybdenum.

Compatibility with grasses and other legumes

Usually grown as pure legume sward for forage or mixed with maize, sorghum or bulrush millet for green chop or silage. Does not compete with perennial grasses because of its annual habit. Pioneer crops of mixtures of cowpea and Japanese millet (Echinochloa sp.) have been used in coastal Queensland, ahead of permanent pastures.

Tolerance to herbicides

Susceptible to MCPB (Gentner and Danielson, 1965). In the United States, trifluralin (Treflan) is used as either a preplant incorporated, preemergence or postemergence herbicide (Johnson, 1970).

Nitrogen-fixing ability

Johnson (1970) estimates fixation at 84 kg./ha if rhizobia are effective. Denarie, Andreamanantena and Ramonjy (1968) found that cowpeas fixed 60 kg. N/acre.

Response to defoliation

Should only be grazed to the stage of leaf removal.

Grazing management

Heavy grazing should be avoided. At no time should it be grazed or cut before flowering. With the 'Havana' type cowpea, Hendricksen achieved only 25 percent recovery when the plant was defoliated before flowering. For quick regeneration, leave four to six buds per plant which can commence regrowth immediately (Hendricksen, 1965).

Response to fire

Will not tolerate fire, but usually is too green to burn.

Dry-matter and green-matter yields

Milford and Minson (1968) found that cowpea yielded 2 310 kg. DM/ha in summer and nil in winter, whereas Lablab purpureus yielded 4 950 kg. DM/ha in summer and 4 070 kg. DM/ha in autumn and early winter. Smith (1961) reported that a Poona cowpea/white Panicum pasture at Cooroy, Queensland, which had been irrigated and fertilized, yielded 27.15 tonnes of green material per hectare at the first grazing. Doherty (1963b) sod-seeded a mixture of mung bean, cowpea and velvet bean into a Rhodes grass/green panic pasture. Cowpeas fertilized with 265 kg. molybdenized superphosphate per hectare planted in 53-cm rows at 9 kg./ha of seed yielded 29 075 kg. green material per hectare.

Suitability for hay and silage

Cowpea makes quite good hay but care must be taken to preserve the leaf. The stem takes some time to dry and should be "conditioned" to hasten drying. It makes good silage if molasses is added to pure cowpea material at 30 to 40 kg. per tonne. It is better mixed with sorghum or maize to provide sugar for fermentation, to add bulk and to prevent protein losses.

Value as a standover or deferred feed

Can be utilized up to the first frost, after which the leaves drop. Not as tolerant of cool temperatures as Lablab purpureus.

Feeding value

  • Chemical analysis and digestibility: 

French (1935, 1937) fed cowpea hay to cattle at Mpwapwa, Tanzania. The crude protein contents were 13.01 and 12.8 percent, and the digestible crude protein 7.92 and 8.70 percent respectively. The seed contains 24 percent crude protein, 53 percent carbohydrates and 2 percent fat.

  • Palatability: 

For the first day or two, cattle may shun the crop, but when they become accustomed to it they will eat it readily.

Seed harvesting methods

Usually by direct heading after frosts have killed the tops of the plants, especially in erect growing crops. For prostrate or trailing varieties, the crop can be mown when two-thirds of the pods are dry and rattle when shaken (in some varieties). The vines should be thoroughly dried before threshing by stationary or pick-up harvesters. Hand picking of pods a number of times during the season gives the highest yields; they can be threshed by flailing in bags or by machine.

Seed yield

Average yield is about 750 kg./ha but reaches as high as 2 800 kg./ha. Gill and Batra (1968) found that cowpeas gave the best seed yield with less than 200 to 250 mm rainfall during growth.

Cultivars

There are numerous local cultivars throughout the world to fill ecological niches. Many varieties are bred for resistance to prevailing diseases. Queensland varieties include 'Santiago, 'Havana', 'Malabar, 'Reeves', 'Cristaudo', 'Poona', 'Black' and 'Blackeye No. 5'.

Diseases

Many recorded­stem and root rots and some pod infections. Phytophthora vignae is most important in Australia (Purss, 1957), and breeding programmes aim at resistance to this disease. Fusarium wilt, septoria leaf spot and mildew are common.

Main attributes

A quick-growing bulky leguminous crop of high protein content, it is a valuable catch crop for building soil fertility. It is drought tolerant and adapted to a wide range of soils.

Main deficiencies

It is an annual susceptible to frost. Thick stems make haymaking difficult.

Performance

Cowpea provides excellent grazing of high food value for dairy cattle and is also suitable for other livestock. Few records of actual grazing performance are available.

Main reference

Johnson (1970).

Latitudinal limits

Between latitudes 30°N and S.

Ability to compete with weeds

Can compete fairly well with low-growing weeds, but not with tall ones such as Tagetes minuta. It is preferably given one or two interrow cultivations if seed has been row-sown.

Pests

Aphis, leaf-hopper and pod borer attacks in Hawaii (Takahashi and Ripperton, 1949); to nematodes and the cowpea witchweed (Alectra vogeli) in Zimbabwe (Johnson, 1970).

Toxicity levels and symptoms

No specific toxicity effects recorded, though it does not tolerate salinity.

Temperature for growth

It prefers warm moist conditions, with a hotter climate than for maize or soybeans (Klages, 1942). Dart and Mercer (1965) found that a day temperature of 27°C gave optimum growth. It is sensitive to cold conditions (Johnson, 197(X). Milford and Minson (1968) found that it dropped from 33 to 14 percent of its leaves in winter. The crop is very susceptible to frost, and in frost-susceptible subtropical areas seed harvesting is usually deferred until frosts have killed and dried the top growth.

Tolerance of drought and flooding

This species is one of the crop legumes most tolerant to drought conditions and is used as a grazing crop and often as a food crop down to 400 mm of annual rainfall in the Sudan. Flooding is usually fatal to cowpeas. They require well-drained soils.

Vigour of seedling, growth and growth rhythm

Quite a vigorous seedling; the young crop can he lightly harrowed during the heat of the day for seedling weed control. Under favourable conditions, cowpeas grow vigorously.

Response to photoperiod and light

The cowpea is usually a short-day plant or indeterminate in its flowering response. Time of sowing has little effect on plant growth, but later plantings flower earlier. Njoku (1958) stated that Nigerian types required a day length of less than 12 1/2 hours for flowering. It is tolerant of moderate shade and so grows with tall crops such as maize and sorghum.

Breeding systems

Normally self-pollinated (Cobley, 1956), in dry areas, but cross-pollination occurs proportional to atmospheric humidity (Purseglove, 1968).

Minimum germination and purity required for commercial sale

A minimum germination of 70 and 98 percent purity, and a maximum of 10 percent hard seed are required in Queensland.

Links:

Links for the genus:

  • Vigna germplasm: Current status and future needs (report prepared by the Vigna Crop Germplasm Committee)