Relationship between soil properties, p sorptioncharacteristics and fertilizer p for optimum yield ofsoybean (Glycine Max (L.) Merr.) on some inceptisols inBenue

Phosphorus (P) sorption influences P requirement of Nigerian soils. Four Inceptisols in Benue state were therefore used to examine the influence of soil properties on sorption indices and yield of soybean. Soil inorganic P was fractionated using standard procedures. Sorption characteristics were determined in 0.01 M CaCl2 solutions of various P concentrations. For each soil, the amounts of P that gave 0.025, 0.05, 0.075, 0.100, 0.125, 0.150, 0.175, 0.200, 0.225, 0.250 mg/kg solution concentration and the buffering capacity were estimated from adsorption curves. In the greenhouse, 4 kg of soil from each location was placed in plastic pots. Amount of P estimated from sorption study was added as KH2PO4. The treatments were laid out in Randomized Complete Block Design (RCBD) and soybean seed variety (TGx 1448-2E) was planted and observed to maturity. At harvest, the shoot was dried, weighed, milled and digested in a 4:1 HNO3:HClO4 mixture and analyzed for P. Optimum solution P concentration (SPC) was determined for each soil in relation to yield. The P adsorption capacities (K) of the soils related significantly to P in biomass (r=0.661). High grain yield (t/ha) was obtained at 0.025 mg P/kg SPC in Abeda-Mbadyul (8.5) and Otobi-Akpa (12.5) while 5.4 t/ha was obtained in Tor-donga and 4.1 t/hain Odobaat 0.10 mg P/kg SPC in the green house experiment. Slightly higher grain yield was obtained at Otobi (6.4t/ha) in the field trial than the estimated SPC values. Buffering capacities of soils varied and related significantly with seed weight (r= 0.605) and P in biomass (r=-0.667). Consequently, Odoba would require highest P fertilizer application (604.84 Kg P/ha), Tor-Donga (112.31), Abeda-Mbadyul (105.93) and Otobi (33.18)