Effect of nitrogen and phosphorus levels on uptake by cowpea (Vigna unguiculata (L.) Walp) and residual N, P and K content in soil

A field experiment was conducted during summer season of 2012 on medium black soil to the study of effect of nitrogen and phosphorus levels on uptake by cowpea (Vigna unguiculata (L.) Walp) and residual N, P and K content in soil. The experiment consisted of four treatments of nitrogen levels (control, 20, 30 and 40 kg/ha) and four treatments of phosphorus levels (control, 40 60 and 80 kg P 2 O 5 /ha) thereby making sixteen treatment combinations tested in Factorial Randomized Block Design with three replications. The results indicated that the application of nitrogen @ 40 kg/ha gave the maximum and significantly higher the N, P and K uptake and residual content in soil and remained at par with 20 and 30 kg N/ha over control. Results further indicated that the application of phosphorus @ 80 kg/ha gave the maximum and significantly higher the N, P and K uptake and residual content in soil and remained at par with 40 and 60 kg P 2 O 5 /ha over control.