Effects of Phosphorus Fertilizer Sources and Application Time on Grain Yield and Nutrient Composition of Cowpea (Vigna unguiculata L., Walp)

The appropriate time to apply water-soluble phosphate fertilizer sources for the production of cowpea (IT84E-2246-4) was evaluated in an Oxic Paleustalf at the Teaching and Research Farm, Ekiti State University, Ado-Ekiti. Cowpea growth and yield were significantly improved by single superphosphate (SSP) and triple superphosphate (TSP), each applied to supply 45 kg P2O5.ha-1. The increase in vegetative growth and nodulation enhanced earliness to flowering and the combined effects produced significantly higher grain yield from TSP and SSP compared to NPK 15-15-15 and the control (0kg P.ha-1) treatments. P fertilizer applied at sowing enhanced early vegetative growth and produced the highest number of nodules, flowers and pods.plant-1 which ensured significantly higher grain yield than withholding the application till 3 and 5 weeks after sowing. The low grain yields obtained from application of P fertilizer at 3 and 5 weeks after sowing were not significantly different which favour applying P fertilizer at sowing time as the recommended practice.