Internal and External Phosphorus Requirements of Maize Genotypes on Typic Calciargid

External and internal phosphorus (P) requirements of hybrid maize (FHY-396) and indigenous variety (EV-7004) were compared on a Typic Calciargid soil. A sorption isotherm was constructed by equilibrating 2.5 g soil with 25 mL of a 0.01 M calcium chloride (CaCl2) solution containing 2, 3, 6, 12, 25, 50, and 100 mg P L-1. Sorption data were fitted to a modified Freundlich equation [x/m = Kf(EPC)1/n] to compute P rates (0, 30, 60, and 120 mg kg-1 soil) against solution levels (0, 0.09, 0.26, and 0.76 mg P L-1) for a pot study. Applied P significantly increased shoot dry matter, P concentration, and P uptake in both the genotypes. For optimum shoot growth, internal P requirement of hybrid (2.51 mg g-1) was 5% more than variety (2.39 mg g-1). However, external P requirement of hybrid (0.50 mg L-1) was remarkably more than variety (0.19 mg L-1). This strongly advocated greater P rates for the high-yielding hybrid than for the variety.