Optimizing phosphorus fertilization for enhanced growth and yield of cowpea (Vigna unguiculata L. WALP) in Sudan savanna agroecology of Nigeria

Phosphorus (P) deficiency is a major constraint to cowpea productivity in tropical soils, yet optimal P rates for Sudan Savanna agro-ecology remain poorly defined. A field study was conducted in 2023 during the rainy season at two locations in Kano, Nigeria, to evaluate the effects of six P rates (0, 20, 30, 40, 50, and 60 kg P/ha) on growth, yield, and physiological traits of cowpea (cv. SAMPEA 14). The experiment utilized a Randomized Complete Block Design (RCBD) with three replications. Data on growth and yield characters were collected and subjected to analysis of variance (ANOVA). Significant means were separated using the Student-Newman-Keuls test. Results indicated that P application significantly (p < 0.05) improved growth parameters, with 40 kg P ha⁻¹ producing the highest leaf area index, number of nodules, leaves, and branches per plant. Yield attributes responded quadratically to P, peaking at 40 kg P ha⁻¹ (1.27 and 1.18 for BUK and Wasai, respectively), beyond which marginal returns declined. Responses were lowest and statistically similar between 0 and 20 kg P ha⁻¹, except for grain yield at both locations, where significantly different responses started at 30 kg P ha⁻¹. Regression analysis confirmed 40 kg P ha⁻¹ as the agronomic optimum for maximizing cowpea productivity in low-P sandy loam soils. These findings provide actionable recommendations for smallholder farmers in Sudan Savanna regions to optimize P fertilization, improve resource-use efficiency, and sustainably intensify cowpea production.