Growth, Yield and Phosphorus use Efficiency of Vegetable Cowpea (Vigna unguiculata) Varieties as Influenced by Phosphorus Levels under Rainfed Conditions of Semi-Arid Environment

Selection of a suitable variety and use of optimum level of phosphorous can significantly increase the productivity and profitability of vegetable cowpea under rainfed conditions in semi-arid tropics. However, application of appropriate level of phosphorus is of prime importance to realize higher yield, economics and phosphorus use efficiency. Hence, a field study was conducted at the Research Farm of Indian Agricultural Research Institute, New Delhi, India to find out the effect of different varieties and phosphorus levels on the growth, yield, economics and phosphorus use efficiency in two consecutive rainy seasons of 2018 and 2019 under semi-arid conditions. Three varieties of cowpea (Pusa Dharni, Pusa Sukomal and Kashi Kanchan) and four levels of phosphorus (0, 20, 40 and 60 kg P2O5 ha-1) were laid out in split plot design with three replications. The results revealed that variety Pusa Dharani recorded significantly higher green pod yield (5.12 t ha-1) with net returns of Rs. 40454 ha-1 and net B:C ratio of 1.27. The maximum nodules per plant, nodule weight per plant and nutrient uptake were also recorded with variety Pusa Dharni. Maximum increase in agronomic phosphorus use efficiency (33.73 kg pod yield per kg P applied) and P recovery (18.19%) were noted with Pusa Dharni. Phosphorus levels showed significant variation on all the growth and yield attributing parameters, and yield. Application of 60 kg P2O5 ha-1 resulted in highest green pod yield (5.38 t ha-1) but remained statistically comparable with 40 kg P2O5 ha-1. However, maximum net returns (Rs.41320 ha-1) and net B:C ratio (1.28) were obtained with 40 kg P2O5 ha-1, whereas 60 kg P2O5 ha-1 could fetched net returns of Rs. 41120 ha-1 and net B:C ratio of 1.22. Highest nodules per plant, nodules weight and N, P and K uptake were registered with 60 kg P2O5 ha-1 and was closely followed by 40 kg P2O5 ha-1. Application of 20 kg P2O5 ha-1 noted highest agronomic P use efficiency (39.72 kg pod yield per kg P applied) and P recovery (15.05%) followed by 40 kg P2O5 ha-1. The highest net returns (Rs. 41345 ha-1), net B:C ratio (1.28), economic efficiency (Rs. 516.81 per day per ha) and production efficiency (66.25 kg per day per ha) were obtained due to the application of 40 kg P2O5 ha-1. Increasing P levels showed positive correlation with nodules per plant, dry weight of nodules, nutrient uptake and pod yield. Hence, the results indicated that growing of cowpea variety Pusa Dharni along with the application of 40 kg P2O5 ha-1 registered to be most suitable to obtain higher net returns and net B:C ratio under rainfed condition of semi-arid regions.