Knowledge of P uptake, utilization and requirements of improved grain amaranth varieties are lacking while the high cost of conventional phosphorus fertilizers limits their use by resource-poor farmers resulting in increased interest in low-cost rock phosphates (RPs) as alternative P sources for grain amaranth production. The study was therefore conducted on the horticultural experimental farm at Ibadan, Nigeria (7 30'N, 30 54'E, 168m a.s.l.). The study was conducted to: (1) determine the optimum P rate for grain amaranth and (2) evaluate P sources and their residual effects under three...