Nodulation and Biomass Yield Response of Cowpea to Row Spacing and Phosphorus Fertilizer Application in the Guinea Savanna Agro-Ecological Zone of Ghana

Phosphorus fertilizer application and planting distance play a major role in the production of shoot, root and nodule dry biomass of cowpea. However, phosphorus is a major limiting nutrient in soils in Ghana. Selection of cowpea varieties that produce good biomass yield under low soil phosphorus or those with high phosphorus response efficiency can be a low input approach in solving this problem in Ghana. Two-season experiments were conducted to evaluate the influence of phosphorus (P) fertilizer and row spacing on growth, nodulation and biomass yield in cowpea. Each of the two experiments comprised of 16 treatment combinations of 4 cowpea varieties, 2 levels of row spacing and 2 levels of P₂O₅ application laid out in a 4×2×2 factorial experiments in RCBD with four replications. The cowpea varieties were IT × P 148, Valenga, Bengkpla and DPC. The levels of row spacing were 60×20 cm and 40×20 cm, whilst the levels of P were 0 and 30 kg ha^-1 P₂O₅. The study revealed that varieties DPC and Valenga performed relatively better with respect to shoot and root dry biomass production, number of nodules produced and nodule dry biomass production across both levels of row spacing and phosphorus fertilizer application. The study further established that row spacing of 60×40 cm and P level of 30 kg ha^-1 also produced significantly higher quantities of shoot and root dry biomass, number of nodules and nodule dry biomass as compared to row spacing of 40×20 cm and P level of 0 kg ha^-1. For the purpose of producing leguminous fodder crops for feeding livestock, varieties DPC and Valenga should be cultivated for improved animal nutrition. Row spacing of 60×40 cm and phosphorus fertilizer application level of 30 kg ha^-1 should also be used for increased biomass yield.