ABSTRACT
Phosphorus (P) is one of the essential macronutrients needed for plant growth but its use efficiency is reduced due to the sorption of a substantial amount added to the soil. The study was conducted on twelve (12) soil samples obtained from four (4) soil depths namely (0-30, 30-60, 60-90 and 90-120 cm) in Ahiara soil series of NIFOR, Benin City, Edo state, Nigeria. Phosphorus sorption influenced by time (kinetics)was determined by equilibrating the soil samples at different times (5, 30, 60, 180, 900 and 1800 minutes) in 25 ml of 0.01 M calcium chloride (CaCl2) containing 50mg L-1 of P as KH2PO4. The physical and chemical properties of the soils were determined using standard laboratory methods while the pseudo-second order kinetic model was used to express the P sorption kinetics at different depths. The data obtained were subjected to statistical analysis using Genstat statistical package. The means were separated at 5% level of probability using Duncan multiple range test. The results from the physical and chemical properties of the soils at the various depths revealed that the soil textural class was Sandy loam, the sand silt and clay had mean values of 817.40, 36.40 and 146.30g kg-1 respectively. The mean values of OC, N, P, K, Ca, Ng and Na were 7.01gkg-1 , 0.35, 0.42 mg kg-1 , 0.26, 0.73, 0.28 and 0.09 cmolkg-1 respectively. The rate of P adsorbed at equilibrium (Qe) was highest at 30-60 cm soil depth with values of 42.92 mgg-1 compared to soil depths of 0-30, 60-90 and 90-120 cm which had values of 26.42, 40.82 and 31.55 mgg-1 .The amount of P adsorbed was inconsistent with increased soil depth. At 5, 60 and 180 minutes, the amount of P adsorbed increased with increased soil depth up to 60-90 cm soil depth (40.82) and decreased slightly at 90-120 cm soil depth (31.55). Considering the pseudo-second order kinetics model, the sub soils (30-60, 60-90 and 90-120) had the highest amount of P adsorbed at equilibrium.
