In this article we will discuss about:- 1. Origin and Distribution of Cowpea 2. Climate, Soils and Tillage of Cowpea 3. Growth and Development 4. Varieties and Seasons 5. Seeding and Plant Population.
Origin and Distribution of Cowpea:
Cowpea might have originated in central Africa or India. Its domestication dates back to 4000 years. It has spread from subsaharian Africa to Middle East and Europe but reached Americas in sixteenth century during the great slave trade. It is now cultivated throughout subsaharian Africa, southeast Asia, Latin America, Australia and USA. The highest cowpea producing nations are Nigeria, India and Brazil.
It is grown allover India, more particularly in the central and Peninsular regions. Maharashtra, Andhra Pradesh, Karnataka, Tamil Nadu, Madhya Pradesh and Rajasthan are the principle states of cowpea cultivation.
There are no records on area production and productivity statistics exclusively for cowpea. Nevertheless, rough estimates indicate that annual global production is around 2 M t from an area around 5 M ha. India accounts for about 0.5 M t production from around 1.5 M ha.
Cowpea (Vigna unguiculata) is the most important grain legume in the third world, particularly Africa. It is commonly known as black-eyed pea, China pea and marble pea. It is an important source of dietary protein in developing countries of Asia and Africa.
It is used as fodder, vegetable, pulse and green manure crop. The economic importance of cowpea is difficult to ascertain, since production statistics no longer kept separate from those of other pulses.
Climate, Soils and Tillage of Cowpea:
Cowpea is essentially a warm weather crop adapted to tropics and subtropics. It tolerates heat and dry conditions and can be successfully grown even in regions with low rainfall of 300-400 mm. It can be grown at wide range of temperatures from 25 -35°C. However, maximum yields are obtained at day/night temperatures around 27°/22°C. It can be grown successfully up to an altitude of 2000 m. It is sensitive to cold and killed by frost.
There are photosensitive and insensitive cultivars. Insensitive cultivars are grown in tropics at lower altitudes. Short day cultivars are grown at higher tropical latitudes for maturation at the end of rainy season. Short day plants when sown early become vegetative. The optimal photopenod for induction of flowering is 8 to 14 hrs.
Cowpea can be grown on a wide range of soils from sands to clays. The primary soil requirements are good drainage and presence of nitrogen fixing bacteria. The crop can thrive well on acid soils and good yields are obtained around pH 6. The crop is moderately susceptible to soil salinity, with an initial yield decrease around 1.3 dS m-1. Tillage requirements are similar to that for other pulse crops.
Growth and Development of Cowpea:
Growth habits of cowpea are erect, semi-erect, trailing, prostrate and climbing. Determinate types with terminal inflorescence are rare. Emergence of cowpea under tropical temperatures averaging 28°C occurs in 2-3 days. The rate of dry matter production by cowpea is closely related to the amount of incoming radiation intercepted by the crop canopy.
The leaves of cowpea are more planophile requiring lower LAI for complete light interception as compared with cereals. Under field conditions, cowpea leaf area development is not limiting if mean temperature varies between 23°and 28°C.
These conditions allow the canopy to attain a LAI of 3 by 35 to 40 days after emergence in stand densities of 7 to 16 plants m-2. A determinate erect cultivar at equidistant spacing can attain growth rates of 16 to 25 g m-2 day-1.
Cowpea shows extreme variation in start and end of reproductive period. Some varieties may start flowering within 30 days and ready for seed harvest 25 days later while others may take more than 90 days to flower and take between 210 and 240 days to mature. Cultivars, which flower early, have shorter blooming period (about 18 days) than later flowering cultivars (30 days), although flowering pattern vary appreciably in different climates.
Plant size (number of nodes produced) at flowering appears to determine economic yield in determinate cultivars. However, many cultivars are indeterminate. Plant size at the beginning of reproductive period is governed primarily by their relative flowering date regulated by their degree of photosensitivity. Thus, large plants can be achieved in photosensitive cultivars by planting under long day conditions, thus delaying the induction of flowering.
Reproductive period of cowpea is composed of overlapping periods of development of individual fruits each of about 19 days duration. The longer the reproductive period, the greater the number of fruits that can be matured and larger the yield.
The environmental conditions that can bring about a shortened reproductive period include hot (day) temperatures, large differences in day and night temperature and drought stress during pod filling period.
Like other legumes, important yield components are number of pods per plant, number of seeds per pod and test weight. Pod number is the most important cowpea yield attribute. The test weight ranges from 8.0 to 8.8 g and number of pods per plant from 20 to 100 for short duration varieties, depending on plant population and other management practices. Dry matter production is a good indicator of final grain yield.
A wide range of yields has been recorded for cowpea. When grown by subsistence farmers as mixed or intercrop, the yield may be around 100 kg ha-1 When grown as sole crop with good management, the yields usually range from 1.0 to 4.0 t ha-1. Crops that are relatively late to flower and mature under relatively cool temperatures have achieved largest yields.
Varieties and Seasons of Cowpea:
A number of improved varieties have been developed to fit in cowpea in intensive cropping systems under varying situations in different states of the country (Table 8.18).
Cowpea is predominantly grown as rainfed crop during kharif both as intercrop and sole crop. Optimum sowing time is first fortnight of June. However, depending on the receipt of monsoon rains, it can be sown up to middle of July. In southern states, short duration cowpea is grown during rabi after kharif rice as an irrigated crop if irrigation water is inadequate for more remunerative crops.
Optimum sowing time is February first week. In north India, it is grown during summer as an irrigated- crop after rabi wheat. April first fortnight is the optimum time of sowing. Generally, short duration varieties are grown during summer.
Seeding and Plant Population of Cowpea:
Sole crop of cowpea is, generally, sown in rows either by drilling or in plough furrows as in the case of other pulses crops. When sown in optimum time, 45 x 10 cm spacing is as good as 30 x 10 cm. However, when seeding is delayed, 30 x 10 cm appears to be ideal. A seed rate of 30 kg ha-1 is optimum for a sole crop.
Depth of sowing is 3 to 4 cm. Optimum plant stand is 10-12 plants m-2. There may not be any yield advantage due to high plant densities up to 30 plants m-2. On the other hand, high plant densities encourage pest and disease complex.