Phosphorus-induced modulation of physiological and yield responses of cowpea under drought stress

Abstract

Cowpea (Vigna unguiculata L.) is a vital legume for smallholder farmers in sub-Saharan Africa, providing protein, livestock feed, and soil fertility through nitrogen fixation. However, productivity is constrained by drought and phosphorus (P) deficiency. This study evaluated moisture regimes (80%, 50%, and 30% field capacity) and P rates (0, 0.5, 2.0, and 4.0 g P?O? plant?¹) on growth and yield of cowpea (cv. CBC1) in a 3×4 factorial RCBD experiment. Drought accelerated maturity by up to 16.8 days, reduced height (35-48%), leaves (35-53%), pods (23-44%), and yield (12.5-29.8%), while increasing 100-seed weight (14.2-33.6%). Phosphorus increased height (19%), leaves (22%), pods (34%), root length (22.5%), and yield (13.5%), but decreased seed weight (16%). Most traits showed additive effects, confirming P cannot substitute for water but partially mitigates drought. Optimal P rates were 2.0-4.0 g plant?¹ under well-watered and 2.0 g plant?¹ under drought, with CBC1 achieving 7.4 t ha?¹. Apply 120-240 kg P?O? ha?¹ when rainfall exceeds 400 mm; 120 kg P?O? ha?¹ under moderate drought (300-400 mm); prioritize moisture conservation when below 300 mm. Field validation and economic analysis are needed.