Growth and nodulation of cowpea [Vigna unguiculata (L.) Walp] as influenced by phosphorus levels and bio-inoculants

Cowpea has unique place in Indian agriculture particularly from the nutritional and soil fertility point of view. Cowpea is well adapted to stress condition and possesses excellent nutritional quality. Its 100 g edible green pod contain 84.6 g moisture, 4.3 g protein, 0.2 g fat, 0.9 g minerals, 2.0 g fiber,  8.0 g carbohydrates etc. It plays an important role by serving as pulse (dry seeds) as well as vegetables (green pod) in subtropical regions. It is extensively grown in the eastern part of the country particularly in U. P. and Bihar. It improves the soil fertility by increasing the amount of nitrogen in the soil through symbiotic nitrogen fixation. It is one of the best components of crop diversification in traditional rice-wheat cropping system (Mortimore et al ., 1997). Vegetable cowpea variety Kashi Kanchan is a short duration crop having bush and erects type of plant. Pods are thick, dark green and slightly curved. Inoculation of leguminous seeds with Rhizobium is considered as the cheapest way of getting atmospheric nitrogen to the plants and soil (Bajpayee et al., 1974). The continuous cultivation of non leguminous crops decreases the nitrogen status of the soil to a great extent. On the other hand, cropping with legumes results in no such depletion of soil nitrogen and also the nitrogen fixed by the legume crops is beneficial to the succeeding crops.  Among various plant nutrients, phosphorus is regarded as the pioneer plant nutrient needed by the leguminous crops for rapid and healthy root development which later on becomes helpful in better nodulation, growth and yield (Prasad and Prasad, 1993). The use of PSB as inoculant increases the P uptake by plants. Simple inoculation of seeds with PSB gives crop yield response equivalent to 30 kg P 2 O 5 /ha or 50 percent of the need for phosphatic fertilizers . Keeping this in view, the present investigation was conducted to study the effect of Rhizobium , PSB and phosphorus on growth and nodulation of cow pea cv. Kashi Kanchan.