Everything you need to know about cowpea cultivation, production and growth. Learn about:- 1. Introduction to Cowpea 2. Origin and Distribution of Cowpea 3. Composition and Uses 4. Climate Required for Cultivation 5. Soil Required for Cultivation 6. Sowing Time 7. Manurial Requirement for Cultivation 8. Irrigation Requirement for Cultivation 9. Intercultural Operations and Few Others.
Contents:
- Introduction to Cowpea
- Origin and Distribution of Cowpea
- Composition and Uses of Cowpea
- Climate Required for Cultivating Cowpea
- Soil Required for Cultivating Cowpea
- Sowing Time of Cowpea Seeds
- Manurial Requirement for Cowpea Cultivation
- Irrigation Requirement for Cowpea Cultivation
- Intercultural Operations of Cowpea
- Harvesting and Yielding of Cowpea
- Cultivated Varieties of Cowpea
1. Introduction
to Cowpea:
Cowpea also commonly known as black-eye pea, black-eye bean, southern pea, China pea, Kaffir pea and marble pea, is cultivated as a seed, vegetable and fodder legume in diverse agricultural systems in many countries of Asia, Africa and Latin America. The prominent cowpea seed producing countries are India, Brazil, Nigeria, and other West African countries.
Chemically mature cowpea seeds contain an average of 23% protein, 60% starch, and 2% oil. The high quality protein of cowpea is also a natural supplement to that of staple grain crops because of its high lysine content but like other legumes, cowpeas are deficient in the sulfur amino acids, methionine, and cystine. The average seed yield of cowpea at the world level is about 380 kg/ha.
Among legumes, cowpea is one of the most important vegetable crops grown as pulse, vegetable or fodder throughout the tropics and sub-tropics during spring-summer and rainy season. Cultivated cowpea is an annual herb with a great range of growth habit and response to photoperiod and great variation in seed-characters. Cowpea species Vigna unguiculata is morphologically and genetically variable and is composed of wild perennial, wild annual and cultivated forms that are mainly used for edible pods and seeds.
According to Pasquet (1999), the cultivated cowpea (Vigna unguiculata var. unguiculata) forms a genetically coherent group and is closely related to annual cowpea (Vigna unguiculata var. spontanea), which may include the most likely progenitor of cultivated cowpea. It is known by many vernacular names like Lobia in Hindi, Barbati in Bengali, Urohi in Assami, Sonta in Garhwali, Chavati in Marathi, Alasande in Kannada and Mampayar in Malayalam.
Cultivated cowpea belongs to three groups, i.e., common cowpea producing 20-30 cm long pods with small seeds, catjang pea producing 7-13 cm long pods with 5-6 mm long kidney-shaped seeds, and asparagus bean or yard long bean producing 30-90 cm long fleshy pods with elongated kidney-shaped 8-12 mm long seeds.
In India, cowpea has been known since the Vedic period and it is grown throughout the country. Long thick podded and trailing type varieties are grown in Kerala, Tamil Nadu, Andhra Pradesh, and West Bengal. In Haryana, Uttar Pradesh, Bihar, and Madhya Pradesh, it is grown for dry seeds, whereas, in Punjab, Gujarat and Madhya Pradesh varieties with short and thin pods like Pusa Do Fasli are preferred.
The annual area cropped under cowpea and its total production in India is difficult to estimate since it is rarely grown as a single crop, however, its total production and yield per unit area have increased over the past decade.
2. Origin and Distribution
of Cowpea:
Vigna is a pan tropical genus containing about 170 species, out of which 120 species are available in Africa, 22 in India and Southeast Asia and a few in America and Australia. There are five subspecies of V. unguiculata, out of which two subspecies dekindtiana available in the African savanna zone and Ethiopia, and mensensis with scabrous and dehiscent pods in forests are wild type.
The most common cultivated sub-species of cowpea is unguiculata and the other cultivated sub-species cylindrica and sesquipedalis are widely spread in India and the Far East but are not found in traditional African farming systems. No theory for the origin of cultivars in Asia can explain the distribution and truly wild status of sub-species dekindtiana, on the contrary, the evidence suggests that the sub-species unguiculata was domesticated from it in Africa.
The spread of cowpea sub-species unguiculata in Asia was around 1500 BC. The expansion of crop in India provided opportunities for genetic diversity from which subspecies cylindrica (for forage) and sesquipedalis (for its long and immature pods eaten as vegetable) originated. From India, the cultivars spread to Southeast Asia or Far East and ultimately reached Europe from Asia and Egypt. Vigna unguiculata (L.) Walp. has been under cultivation in India since ancient time.
3. Composition and Uses of Cowpea:
Composition:
The green pods are rich in protein, vitamin B, and minerals. Cowpea is a rich source of lysine and tryphtophan. The proteins of cowpea are of high biological value. It can fortify the carbohydrates rich diet appreciably to improve the nutritive value of food. The presence of anti- nutritional factors such as hydrate, oligosaccharides, and protease inhibitors had also been reported in dry seeds of cowpea. The composition of green pods and seeds is given in Table 2.1.
Uses:
Cowpea is grown for its tender pods for culinary purposes. Dry seeds are used as pulse. From nutritional point of view, it is one the important vegetables grown in India and a large number of dishes can be prepared from the pods and developed grains. The green pods are used for vegetable and soup, while green and dried seeds are used for vegetable like pea, and for different type of dishes.
It is also used as green manure crop and a fodder. On account of its ability to fix nitrogen in the soil, cowpea meets its own requirement and leaves a fixed nitrogen deposit in the soil up to 60-70 kg/ha for succeeding crop. The crop produces heavy vegetative growth and covers the ground so well that it checks soil erosion as well as growth of weeds.
4. Climate Required for Cultivating Cowpea:
Cowpea, being warm season crop, can be grown successfully in all tropical and sub-tropical areas but cannot withstand cool weather, thus, not possible to grow it in regions with cool or temperate climate. It can tolerate short duration drought but cannot withstand heavy rainfall and water logging conditions. The germination is better at a temperature ranging from 12° to 15°C, but the crop thrives best between 21° and 35°C.
The crop can tolerate partial shading but being susceptible cannot tolerate frost. The varieties show varying response to temperature and day length, and hence, the varieties are different for spring-summer and rainy season. Growing cowpea in the state of Kerala is not beneficial due to excessive rain.
Coconut plants reduce cowpea yield significantly by causing shade, however, dry matter production is less affected by shading. Shading also exerts detrimental effects on leaf area index, specific leaf area, leaf weight ratio, nodulation, and net assimilation rate. Leaf area index. (LAI) is not so affected by shading up to 60 days after sowing, but thereafter, it declines rapidly.
5. Soil Required for Cultivating Cowpea
:
Cowpea can be grown on all types of soil having pH from 5.5 to 6.5, however, well drained and humus-rich sandy loam soils are the best suited for its economic yield. Being sensitive to poor aeration and water logging conditions, clay soil is not at all suitable for it. In addition, the crop is sensitive to high pH, thus, saline or alkaline soils are also not suitable for its successful cultivation.
One deep ploughing followed by two or three shallow ploughings is required for obtaining fine tilth. Remove all the stubbles of the previous crop to prepare clean and smooth seedbeds. The last ploughing should be followed by planking to level the field.
6. Sowing Time
of Cowpea Seeds:
In most parts of the country, cowpea is grown both in spring-summer and rainy season. Sowing in June-July is common for rainy season crop, but it could be extended up to August, especially for early maturing bush type varieties. Similarly, sowing in February-March is common for spring-summer crop, particularly in northern plains, which could be extended up to mid-April.
It is also grown in winter months in areas with mild climate. In hills, it is sown from April to July but in southern plains, the optimum sowing time is December-January. It can be grown throughout the year in places like Bangalore where the climatic conditions are mild. Being short duration crop, it fits well in sequential cropping systems and as an intercrop with widely spaced vegetables and other crops like maize. It is grown as a catch crop after the first crop of paddy or after late winter crop.
It is also grown as a cover crop in fruit orchards. Under Bangalore conditions, sowing done in July gives the highest fresh green pod yield. In semi-arid areas (Jobner, Rajasthan), the highest seed yield (890 kg/ha) is obtained when sowing is done on 23rd July. In the state of Maharashtra and particularly at Mahatma Phule Krishi Vishvavidyalaya, Rahuri, the seed yield decreases with successive delay in seeding.
Sowing done on June 1st gives the highest seed yield (1660 kg/ha). At Patharchatta (Uttar Pradesh), it has been found that sowing done in last week of June gives the highest fresh green pod yield, however, delayed sowing causes decrease in yield.
The seed rate varies with the growing season, variety used, soil type, and irrigation facilities. Usually a seed rate of 20-25 and 12-15 kg is enough for the sowing of one hectare land area in spring-summer and rainy season, respectively. In mixed sowing with other crops, the seed rate may be reduced to half. A population of 1,11,111 plants may be accommodated in an area of one hectare to harvest best yield of fresh green pods.
Seed dormancy is found in no way in cowpea cultivars, and hence, no treatment is required for breaking dormancy, however, if the crop is sown for the first time in field, the seeds should be inoculated with Rhizobium culture since it helps in quick nodulation of roots for symbiotic nitrogen fixation. Dissolving 125 g gur in 500 ml of water, a solution is prepared and sprinkled over seeds required for sowing one-hectare area and mingled to moisten them.
A packet of Rhizobium culture is poured over the seeds and mixed thoroughly with hands so that seeds are uniformly coated with culture, thereafter, the seeds are placed in shade for few hours before sowing for the completion of inoculation, and subsequently, the seeds are sown as usual.
As precautionary measure after inoculation, the seeds should not be exposed to sun and high temperature too since the Rhizobium bacteria being sensitive may destroy. Cowpea seed yield is increased by about 25% by seed fortification with a mixed application of zinc sulfate 0.5%, manganese sulfate 0.5% and sodium molybdate 0.1% plus pelleting with diammonium phosphate 120 g/kg seed.
Cowpea can be sown by broadcasting but sowing in lines, which can be done with a seed drill operated by tractor, bullocks, or manual labour, facilitates better intercultural operations and aftercare. The seeds are sown at a depth of 2-3 cm directly in flat seedbeds in spring-summer and on raised seedbeds in rainy season keeping a row-to-row spacing of 30 and 45-60 cm, respectively.
The plant-to-plant distance is kept 15-20 cm, depending upon season of growing. Under Bangalore conditions, a spacing of 30-45 × 10 cm gives good seed yield. According to Singh et al. (1992), a spacing of 30×15 cm gave the highest fresh green pod yield under conditions of Punjab.
The lowest yield is obtained under conditions of Maharashtra when the crop is sown on flat seedbeds but it is harvested the highest when sowing is done in the centre of furrows and after about a month modified into ridges keeping the plant stems in the centre. Seed yield of cv. Pusa Barsati is found the highest when the crop is sown at a spacing of 60 × 15 cm. A spacing of 45 × 10 cm gives the highest yield at Hisar in the state of Haryana.
Sowing done on tied-ridge seedbeds in comparison to flat sowing has been found to be useful as it eliminates or reduces run-off, increases soil water storage and reduces severe seed yield losses during protracted dry spells in the Sudan Savanna zone (in Nigeria) especially on an Alfisol. However, they have no effect on cowpea yield in the northern Guinea Savanna zone on an oxisol.
In Alfisol, tractor ploughing and early sowing is adequate to reduce run-off, and the cowpea is subjected to severe yield loss during dry periods. When cowpea cv. C-152 is intercropped with cassava cv. M-4 under Thrissur (Kerala) conditions, higher seed yield is obtained as compared to another cultivar New Era.
Gross returns and cost-benefit ratio have been found to be the highest when cassava is intercropped with cowpea cv. Pusa-2 or New Era. In Nigeria, cowpea in cowpea-okra-tomato cropping sequence has the highest nodule weight at 10 weeks after sowing. Intercropping cowpea with cassava significantly reduces plant height, yield, and number of roots of cassava.
Intercropping cassava does not affect cowpea yield, however, establishing cowpea on the same date as cassava gives higher yield of cowpea than that is obtained when cowpea is introduced later. Studies conducted by Dutta and Thakuria (1994) at Jorhat (Assam) reveal that teosinte [Euchlaena (Zea) mexicana] and cowpea intercropping in the row ratio of 1 : 1 gave the highest land equivalent ratio (1.34) monetary returns.
7. Manurial Requirement
for Cowpea Cultivation:
Though cowpea is a legume crop, it responds well to the application of fertilizers. About 25 tonnes of well-composted organic manure is applied to the soil at the time of land preparation since the cowpea yield increases with the application of organic manure in combination with inorganic fertilizers.
Application of nitrogen 25 kg, phosphorus 75 kg, and potash 60 kg/ha is recommended. Half dose of nitrogen along with entire dose of phosphorus and potash fertilizers are applied at the time of last ploughing, and the remaining half of nitrogen is applied at the time of earthing up after 3rd week of sowing.
Kumar et al. (1990) recommended a fixed dose of nitrogen 75 kg/ha, however, in Punjab, 50 kg of nitrogen (112.5 kg of urea) as starter dose, 40 kg of phosphorus (250 kg of super phosphate) and 25 kg of potash (40 kg of muriate of potash) per hectare has been recommended. In zinc deficient soils, zinc sulfate 10- 15 kg/ha may be applied at the time of sowing since spraying of micronutrients improves the quality besides increasing the crop yield. The dose of nutrients may be calculated based on soil test values to economize the fertilizers.
Application of phosphorus 60 kg/ha increases NPK content by 7.83, 8.18, 9.62 and 12.76, 6.03, 6.03% in seed and Stover, respectively. The NPK content also increases by 5.34, 8.68, 8.02 and 11.85, 7.03, 7.03% in seed and Stover, respectively by the application of farmyard manure 15 t/ha. At 60 kg P2O5/ha, the nutrient uptake in seed, Stover, and total uptake of NPK increases by 95.27, 97.14, 93.27, 44.14, 40.63, 35.27 and 54.47, 81.09, 38.54%, respectively.
Farmyard manure application @ 15 t/ha results in 37.16, 38.25, 35.83, 31.06, 29.86, 27.94 and 33.98, 36.19, 28.48%, respectively more NPK uptake over control. The maximum chlorophyll, chlorophyll ‘a’, chlorophyll ‘b’ carotene and pod yield is favored by the application of phosphorus 90-100 kg/ha followed by 60 kg/ha.
The beneficial influence of phosphorus on chlorophyll and carotene contents of cowpea leaves may be due to availability of higher energy in the form of ATP molecules, which may favour the multiplication of cells. Chlorophyll content is reduced at post anthesis stage of cowpea, which can be due to reduced photosynthetic rate.
Pod yield of cowpea is increased correspondingly with increasing level of phosphorus. Cowpea responds positively though non-significantly to nitrogen fertilization up to 30 kg/ha, however, nitrogen has no effect on nitrogen, phosphorus, potash, and boron content of index leaves. Application of boron has no effect on nitrogen, phosphorus, and potash concentration of index leaves but increases boron concentration highly significantly.
Boron application reduces seed yield. The critical level of boron toxicity in index leaves is approximated to be 21 ppm. Agbenin et al. (1991) observed that when nitrogen was applied @ 60 and 120 µg per g soil, it increased growth components, dry matter yield, and nutrient uptake over the control (N0B0). Urea was source of nitrogen and sodium tetraborate the source of boron. A critical level of boron toxicity in plant tissue was approximated to be 30 ppm.
There was no significant nitrogen and boron interaction effect on various parameters. When standard basal doses of nitrogen and phosphorus are applied, soil amendments help in the utilization of applied zinc. In sodic soils, the cowpea seed and Stover yield is obtained highest with the incorporation of dhaincha (Sesbania aculeata) plus gypsum along with the application of zinc sulfate 37.5 kg/ha. Krasilnikoff et al. (2001) noticed that phosphorus uptake differed considerably between cowpea genotypes, which might be attributed to varying lengths of root hair (0.23 to 0.38 mm).
Increasing phosphorus rates from 0 to 75 kg/ha in Dapoli (Maharashtra) increases seed yield under artificial conditions. Application of nitrogen and boron suppresses nodulation. Seed yield of cowpea increases with an increase of phosphorus rate from zero to 50 kg/ha but not increased further with the application of phosphorus 75 kg/ha. Seed yield of cowpea can be improved substantially by top dressing with moderate rate of phosphorus (70 kg/ha) in Queensland (Australia) provided the phosphorus deficiency is identified sufficiently early, i.e., 14 or 21 days after sowing.
The plant growth and yield are not significantly affected by phosphorus rate (25-75 kg/ha) under Bangalore conditions in the Karnataka state. Source of phosphatic fertilizer matters much in determining the growth and yield of cowpea. Seed yield is harvested highest with the combination of Missouri Rock Phosphate (MRP) 50 kg P2O5/ha and organic manure (Aspergillus awamori inoculums) under Karnataka conditions.
The crop growth and yield increase significantly with increasing rates of phosphorus up to 37 kg/ha, which gives 54% higher seed yield than the control. The interaction of phosphorus dose and cultivar influences seed yield significantly, and the interaction of phosphorus source and cultivar significantly influences the seed yield, onset of flowering, number of flowers, pod weight, and seeds per plant.
Under Port Blair conditions in Andaman Islands, application of a combination of nitrogen 50 kg/ha and phosphorus 75 kg/ha gives the highest seed yield of cowpea. Phosphorus application also increases moisture extraction from zero to 90 cm depth, consumptive water use and water use efficiency.
Nitrogen does not affect the nodulation but increases dry matter production, while in case of phosphorus, the root nodulation is increased without any effect on dry matter production. Seed yield is obtained highest with nitrogen, phosphorus, potash, and sulfur @ 20 : 60 : 30 : 20 kg/ha. Phosphorus application enhances seed yield by favouring an increase in branches per plant, pod length, seeds per pod, pods per plant, and 100 seed weight.
NPK fertilizer application significantly increases nodule counts and root weight after sowing cowpea sole crop as well as in cowpea-okra-tomato and cowpea-maize-okra-tomato cropping systems, but the application of potassium affects neither nodulation nor dry matter production. Although fertilizer application increases more nodulation in the intercrops, yet it results in a lower seed yield of cowpea.
When cowpea is intercropped with maize at Vellayani (Kerala) cowpea seed yield is not significantly affected but maize fodder yield decreases under paired or triple rows of cowpea. It is further observed that cowpea seed yield remains unaffected by the NPK fertilizer doses but maize fodder yield is decreased by decreasing the NPK dose.
Soaking of seed in 100 ppm potassium dihydrogen phosphate and Rhizobium inoculation improves seed germination. This seed treatment if supplemented with 30% less nitrogen than the recommended dose of nitrogen 25 kg/ha also gives the highest seed yield. Phosphorus application increases nodulation significantly, however, the extent of nodulation varies with the genotype/cultivar. At Abeokuta in Nigeria, the cv. IT86D- 1038 gave the best response (225 nodules per plant) when phosphorus was applied 30 kg/ha.
The high phosphorus rate significantly reduces the number of days to 50% flowering by 5-8 days, irrespective of genotype, unlike the seed yield. Phosphorus fertilization also increases the quality parameters, viz. dry matter yield and crude protein content. A combination of nitrogen 20 kg/ha and phosphorus 80 kg/ha gives the highest seed yield of rainy season crop at Jabalpur (Madhya Pradesh). Dry matter yield and crude protein content increase with increasing phosphorus rate up to 30 kg/ha with no further increase at higher rate.
Aspergillus awamori inoculation coupled with the application of Missouri Rock Phosphate (MRP) 50 kg/ha gives the highest seed yield. Bradyrhizobium culture improves nodulation and nitrogen fixation. Plant Growth Promoting Rhizobacteria (PGPR) is better than Bradyrhizobium, and consortium of three isolates of PGPR further improves all the plant growth parameters.
Cowpea Bradyrhizobium strains help in better nodulation, but fixation of nitrogen is not appreciably influenced by inoculation. Growth and yield of cowpea may change in response to organic amendment, and it is attributed to differential effects of the type of amendment on the proliferation of different arbuscular mycorrhizal fungi.
According to Muthukumar and Udaiyan (2002), cowpea growth and yield are more positively correlated with spore populations of Glomus aggregatum, G. geosporum, and Scutellospora calospora and negatively correlated with Acaulospora scrobiculata and Glomus sinuosum.
Application of a combination of nitrogen 20 kg/ha and phosphorus 80 kg/ha gives the highest seed yield under conditions of Jabalpur. Increasing levels of phosphorus and potassium each up to 80 kg/ha as basal dressing increase the fresh green pod yield in Nainital soils. Nutritional requirements including Rhizobium application have been worked for the production of vegetable cowpea under Andaman and Nicobar Island conditions.
Maximum pod yield is obtained with the application of 60 kg/ha over control, however, it is statistically at par with 120 kg/ha. Maximum green pod yield (96.9 and 128.37 q/ha) is obtained with the application of phosphorus 80 kg/ha. The combined application of phosphorus 80 kg, potassium 60 kg and nitrogen 20 kg/ha with Rhizobium inoculation 150 g/3 kg of seed just half an hour before sowing produces significantly higher yield of green pods (147.35 q/ha) compared to control N0P0K0 (65.20 q/ha).
Earlier studies of Mishra and Solanki (1996) also revealed similar results, and application of nitrogen 20 kg/ha + Rhizobium inoculation recorded the maximum yield. Application of vermi-compost results in higher fresh and dry weight yield, and application of vermi-compost enriched with rock phosphate improves growth and yield of cowpea.
8. Irrigation Requirement
for Cowpea Cultivation:
Cowpea, being a shallow rooted crop, may not be grown successfully under rain fed conditions, but can be cultivated with two or three protective irrigations, depending on the atmospheric conditions. At the time of sowing, the soil must have adequate moisture, which is essential for optimum seed germination.
Under such situation, the irrigation is delayed until the seedlings emerge out of soil, however, if the field is not having moisture enough for seed germination, the first irrigation should be applied just after sowing. In general, light irrigation is given at weekly interval in spring-summer and as and when required in rainy season since the crop is sensitive to both drought and water logging conditions. Flowering and pod development are the critical stages for irrigation.
Sensitivity of the cowpea cultivars to water stress varies with cultivar. Early maturing cultivars are more sensitive to drought than the late maturing ones. This sensitivity is shown by a very high water stress index. Simple regression between seed yield and various field crop parameters such as phenology, development, and yield components shows that the preservation of number of seeds per square meter is an interesting criterion.
Maintenance of proper water balance and economy in fertilizer use is of great importance in semi-arid areas of North India where daily water intake is very high and moisture stress is developed within a short period, thus, the adverse effect of dry spell may be eliminated by giving irrigation at the most critical time, if known. Such irrigation may also increase response of other management practices, of which fertilizer is an important factor.
Flooding or water logging of clay soils during wet season or deficits in dry season can reduce crop yield. Simpson and Gumbs (1985a, b; 1992) reported that cowpea production is more sensitive to excessive moisture. Turk and Hall (1980a, b) reported yield reductions up to 50% when drought stress occurred during the sensitive floral initiation to fruit set stages.
Flooding the soil at vegetative stage for 1, 2, 4, or 6 days significantly reduced several vegetative plant growth, parameters, viz. plant height, leaf number, leaf area, leaf and stem dry matter and root dry weight, however, flooding for 1 or 2 days at flowering and pod set stages did not significantly affect any of the plant growth parameters.
Irrigation when applied at 100 mm of cumulative pan evaporation (CPE) results in higher moisture extraction from zero to 90 cm depth. Water use efficiency (WUE) of cowpea is measured highest when irrigation is given at 150 mm CPE.
Irrigating the crop at critical stages of growth, viz. seedling, flowering and seed development, results in good seed yield (0.55 t/ha), however, the production can be further increased from 0.68 to 1.31 t/ha if the crop is irrigated keeping in view the ratio of irrigation water depth to cumulative pan evaporation. Irrigation water depth to CPE ratio of 1.5 gives the highest seed yield (1.31 t/ha).
Cowpea uses 60-67, 24-30, and 8-10% water from 0-30, 30-60 and 60-90 cm soil depth, respectively, indicating that soil moisture use decreases with the soil depth. The soil depth of 0- 60 cm contributes to about 68-69% of the total soil moisture used by cowpea. Variety Russian Giant extracts more water from zero to 60 cm as compared to other varieties. This may be due to the variations in root characteristics of cowpea varieties.
Moisture depletion from zero to 30 cm depth is higher from phosphorus-unfertilized fields/plots than fertilized plot but moisture depletion is more in case of phosphorus-fertilized plot from 30 to 90 cm depth. This may be due to vigorous growth and extension of roots to the deeper layers under phosphorus-fertilized plots.
Consumptive use of water increases with the application of phosphorus. It is measured highest with phosphorus 60 kg/ha and the lowest in control. It is because of the fact that phosphorus application helps in root development and vigorous growth. Water use efficiency (q/ha/cm) increases progressively with the application of phosphorus over control. It is found maximum with phosphorus 40 kg/ha.
Presence of salts in irrigation water affects the growth in respect to plant height and number of leaves per plant since presence of higher level, ranging from 2.5 to 20 meq/litre, of residual sodium carbonate in irrigation water decreases the plant growth and uptake of nitrogen, phosphorus, and potash ions, however, there are some varieties that can tolerate the adverse effects in a better way than the others.
The cv. Russian Giant has been found to be comparatively more tolerant to sodic irrigation water than the cv. Pusa Barsati. Micro-sprinkler irrigation gives 27% higher grain yield than that for surface method of irrigation, and it saves 21% of irrigation water thereby resulting in higher water use efficiency. Micro- sprinkler gives a benefit/cost ratio of 1.54 when considered with system cost and 2.00 considered without system cost.
9. Intercultural Operations of Cowpea:
i. Hoeing and Weeding:
Tillage does not significantly affect plant growth and seed yield of cowpea on clay soil. Continuous no-tillage can lead to the establishment of weed species, which are difficult to eradicate, however, weed control will have to be considered in the development of cropping system, which includes long duration no-tillage cultivation. Alternatively, the cropping system, which includes a tillage cycle, will facilitate weed control.
Simpson and Gumbs (1992) have recommended a rotation of cowpea in the minor wet season under the rainfall pattern in Guyana but this cropping system occupies the land for six months of the year. The production of a second crop of cowpea in wet season without tillage or in dry season with or without irrigation is desirable.
The major weeds that pose problem to cowpea crop are Ageratum conyzoides, Commelina bengalensis, Euphorbia heterophylla, Cyperus rotundus, C. compressus and Echinochloa colonum. If the crop field is kept weed free, optimum seed yield can be obtained in both dry and wet seasons. Shallow hoeing to keep the field weed free and to provide aeration to the roots is desirable, especially during first 45 days after sowing.
For this purpose, two hoeings are sufficient at 25 and 45 days after sowing. Application of chemicals such as Oxadiazon 0.5 kg, Alachlor 1.5 kg, or Nitrofen 3.0 kg/ha as pre-emergence has been found effective in controlling weeds in cowpea field. At later stages of crop growth, the weeds are kept under check due to dense crop canopy.
In cowpea, there are two types of varieties such as bush type and vine type. Bush type varieties can be grown successfully without trailing them. However, the vine type varieties need support since the plants have twining growth habit. Because of this reason, such varieties are generally restricted to kitchen gardens, but in eastern Uttar Pradesh, they are grown as mixed crop with sorghum. The bush type varieties can also be intercropped with maize. Cowpea is suitable to fit in several cropping sequences consisting of cereals and vegetables.
Mulching can influence the microenvironment of cowpea field. Mean soil temperature below the mulches does not vary too much, differences being less than 1°C. This much soil temperature difference is not sufficient to cause major differences in plant growth and yield but differences in reflected light spectra are sufficient to cause such variations.
Light reflected from black and white mulch surfaces have far red (FR) to red (R) ratio of 1.05± 0.05. Red mulch reflects light with mean FR/R ratio of 1.25±0.05. Pod yield is influenced with different mulch colors. Cowpea grown over red mulch has numerically higher pod yield than that grown over white and black mulches. This is attributed to the fact that red surface reflects light with higher FR/R ratio than black or white surface.
Earlier studies by Kasperbauer and Hunt (1987) also revealed influence of soil and surface residue colour on spectral balance of canopy light and recorded differences in the height of cowpea plants. Mulching with straw or black polyethylene improves seed yield although not significantly. Soil moisture is increased in zero to 15 cm layer by mulching.
Mulching with rice straw 4 t/ha does not affect compaction but decreases diurnal soil temperature and increases wetness. Mulching in combination with minimum tillage is most appropriate soil management system for cowpea production in the dry season in rice fallows of inland valley swamps in Ibadan, Nigeria.
iv. Use of Plant Growth Substances:
Application of growth substances is beneficial for growth and yield of cowpea. Spray of gibberellic acid (GA3) 40 ppm at 10-45 days after sowing gives the highest seed yield since GA3 enhances leaf nitrogen content, while it does not affect the phosphorus and potassium contents. On the other hand, application of 2,4-D gives the lowest yield. Shinde et al. (1991) reported that among growth substances (NAA, KNO3 and Ethanol), NAA 5 ppm gives the highest seed yield (1.53 t/ha).
Soaking of seeds in the solution of growth substances before sowing also proves beneficial. Seed germination is improved with 10 ppm GA3 when used for seed soaking for 24 h before sowing. The average pod yield decreases with an increase in GA3 concentration up to 60 ppm. Both GA3 and NAA give higher yield than the untreated control.
Indole acetic acid (IAA) 10 ppm and Indole butyric acid (IBA) 10 ppm improve germination, dry matter production, flowering, and seed yield per plant when applied as seed treatment before sowing. Maleic hydrazide (MH) reduces germination rate, dry matter production, flowering, and seed yield. The effect of MH is not alleviated by the application of either IAA or NAA.
10. Harvesting and Yielding of Cowpea:
Quality of pod is the most important consideration in cowpea as over-matured pods result in more toughness, whereas, less matured pods result in low pod weight. Light green, tender, thin, medium long (15-18 cm), straight, round fleshy without parchment layer and non-stringy with good keeping quality pods are preferred more by the consumers in the markets. The pods for table use are harvested when they are developed adequately but still tender and non-fibrous.
Picking of pods 15 days after pod setting is ideal for vegetable purpose compared with other picking stages since the pods at this stage are longer and less fibrous with more protein content and are more succulent. Similar results have been reported by Sambandam et al. (1965). Harvesting that starts from 45-50 days in early cultivars may continue up to 100 days in flushes. Bush type varieties give 3-4 pickings and pole types 5-6 pickings.
The seed crop matures in 75-125 days, depending on season and variety. Generally, for seed purpose, the pods are allowed to attain full maturity on plants, and then, the crop is harvested and threshed after proper drying. If grown on a smaller scale, the mature pods are picked-up at regular intervals.
Depending upon variety used, soil type, growing region and season, and cultural management practices followed for raising the crop, the green pod yield varies from 75 to 100 q/ha and seed yield from 10 to 15 q/ha.
For remunerative price, it is better to remove the insect-pest and disease damaged pods before marketing. Similarly, fibrous and over-mature pods should also be sorted out. For seed purpose, the harvested pods are dried for few days before threshing. The threshed seeds are also dried sufficiently before storage in a cool and dry place. The green pods can be stored at room temperature for two to three days provided they are frequently sprayed with cold water. In cold storage, pods can be stored for 15-20 days at 0°C temperature coupled with 85-90 per cent relative humidity.
11. Cultivated Varieties of Cowpea:
The main criteria for the development of varieties for vegetable purpose have been the pod yield and its quality. Generally, the varieties for fresh green pods and for dry grains are different, however, there are some dual purpose varieties that may be grown for fresh green pods as well as for dry grains.
A photosensitive dwarf type variety developed at Indian Agricultural Research Institute, New Delhi through selection from ‘Dolique du Tonkin’—an introduction from Canada is suitable for spring-summer sowing. Pods are dark green, straight, and 12-15 cm long. It becomes ready for harvest 60 days after sowing and yields 50-100 q/ha.
A photosensitive early maturing variety developed at Indian Agricultural Research Institute, New Delhi through selection from a collection introduced from Philippines is suitable for growing in rainy season. It flowers in 35 days and becomes ready for harvesting in 45 days after sowing. Pods containing large light green seeds are 25-28 cm long, pendent, light green, and borne in 2-3 flushes. It gives green pods yield of 80 q/ha.
A photo-insensitive dwarf type variety developed at Indian Agricultural Research Institute, New Delhi through a cross Pusa Phaiguni × Philippines Selection is suitable for cultivation both in spring-summer and rainy season due to its photo-insensitive nature. Pods are thin, light green, straight, and 18 cm long. Its first picking starts 50 days after sowing. It produces about 75-80 q of green pods per hectare.
A photo-insensitive bushy variety developed at Indian Agricultural Research Institute, New Delhi through a selection from germplasm collected from National Bureau of Plant Genetic Resources, New Delhi is suitable for cultivation in both spring-summer and rainy season. First picking is possible in 40-50 days. Pods that are 20-25 cm long virtually cover the foliage. It is a dual- purpose variety grown both for fresh green pods and grains too. Its green pod yield potential is 80 q/ha.
A photo-insensitive widely adaptable indeterminate variety developed at Indian Agricultural Research Institute, New Delhi through a cross P-85-2 × P-426 is resistant to bacterial blight, hence, suitable for rainy as well as spring-summer season. Its 25-30 cm long light green pods are harvested in 2-3 pickings. Its green fresh pods yield is 100 q/ha.
A variety developed at Indian Institute of Horticultural Research, Bangalore through backcross and pure line selection from the cross TUV-762 × Vigna unguiculata ssp. sesquipedalis is tolerant to heat and drought. Plants are tall, vigorous, bushy, and spreading with small vines and light green leaves. Long thick pods are light green, round, fleshy and stringless. It gives on an average fresh green pod yield of 180 q/ha. It is recommended for cultivation in Zone VII (Madhya Pradesh and Maharashtra) and VIII (Karnataka, Tamil Nadu, and Kerala).
A photo-insensitive early maturing variety developed at Indian Institute of Horticultural Research, Bangalore through pedigree selection from the cross of Arka Garima and Pusa Komal is suitable for cultivation in Zone VI (Rajasthan, Gujarat, Haryana, and Delhi) and VII (Madhya Pradesh and Maharashtra). Plants are 70-75 cm tall, erect, and bushy in growth habit. Pods are green, medium thick, medium long (15-18 cm), tender fleshy without parchment layer and good in keeping quality. It gives on an average fresh green pods yield of 190 q/ha in 70-75 days of crop duration.
An early maturing variety comparatively resistant to cowpea mosaic virus and free from cowpea golden mosaic virus developed at Punjab Agricultural University, Ludhiana through a selection from Bangalore Local is recommended at the national level and suitable for cultivation in both spring-summer and rainy season. Its green fleshy pods are medium long (about 20 cm), thick, and tender. The average yield of fresh green pods is 88 q/ha.
A late type variety belonged to sub-species sesquipedalis is commonly cultivated in kitchen gardens of Uttar Pradesh. Its plants that require support are vine type. Pods are long up to 50 cm and not suitable for transportation because they break up during transition. It gives fresh green pod yield of 100 q/ha in crop duration of 100 days.
A trailing type variety is popular in Madhya Pradesh. Pods that become ready for picking 55-70 days after sowing are 29 cm long, creamy white and non-stringy with 17 seeds per. pod. It produces fresh green pod yield of 60-90 q/ha in crop duration of about 75 days.
A photo-insensitive variety developed at Narendra Deva University of Agriculture and Technology, Faizabad from a cross Pusa Komal × Varanasi Local and following pedigree method, is suitable for cultivation in both spring-summer and rainy season. Plants are 40-45 cm tall with determinate growth habit and foliage is green with large leaves. Pods that become ready for first picking in 40-48 days are 28-32 cm long with purple terminal end, and each pod contains 10-12 seeds, which are bold with black helium. Its fresh green pod yield is about 75-80 q/ha. Seed maturity takes 75-80 days after sowing.
A variety with 70-75 cm tall plants developed at Narendra Deva University of Agriculture and Technology, Faizabad is suitable for sowing in rainy season and recommended for cultivation in Zone IV (Punjab, Uttar Pradesh, and Bihar). Pods are green, 30 cm long and black seeded. Its average fresh green pod yield is 80 q/ha. It is susceptible to Pseudocercospora and viruses.
A variety developed at Bidhan Chandra Krishi Vishwa Vidyalaya, Mohanpur (Nadia) West Bengal is resistant to cowpea mosaic and cowpea golden mosaic virus. Plants are compact and determinate with dark green foliage. Pods that take 55-70 days for first picking are 25.2 cm long thick and fleshy. The seeds are bold, thick, slightly reniform, Holstein coloured with buff and brown specks.
A variety developed at Bidhan Chandra Krishi Vishwa Vidyalaya, Mohanpur (Nadia) West Bengal shows very less incidence of cowpea mosaic and golden mosaic virus. Plants are semi-determinate and loose framed with yellowish green foliage. Light green solid pods that take 55-60 days for first picking are 25.8 cm long, tender, thick, and fleshy. Its seeds are flat, reniform, and Holstein coloured with buff and dark tan specks.
A dual-purpose medium duration variety developed at Kerala Agricultural University, Vellanikkara matures in 65-70 days in spring-summer and 75-80 days in rainy season. It yields fresh green pods of 75 q/ha.
Besides, S-203 derived from a cross Sel-2 × Virginia, S-488 from Virginia × Iron Grey, Aseem from Pusa Do Fasli × Philippines, Bush, BCKV-1 and BCKV-2 are the other varieties of cowpea grown in different parts of the country.