Use of sorption isotherms to evaluate phosphorus requirements of some savannah soils of western nigeria
Ayodele, O.J.; Sobulo, R.A.; Agboola, A.A.
Tropical Agriculture 61(3): 226-229
The P sorbed by 9 savannah surface soils (0-15 cm) and 1 subsoil was determined after equilibration in 0.01 M CaCl2 containing various P concentrations for 15 min, 30 min, 1 h, 4 h, 6 h, 12 h, 17 h and 24 h. The capacity of soils to decrease solution P concentrations increased with equilibrium time. Amounts of P sorbed from a solution containing 100 mg P/100 g initially increased rapidly and appeared to attain an equilibrium with the surface soil samples in .apprxeq. 6 h. The soils had low P sorption levels when compared with many tropical soils. P sorptions at 6 h equilibration time varied between 0.8-23 and 3.4-42 mg kg-1 soil at 0.2 and 2.0 mg dm-3 equilibrium concentrations, respectively, and correlated with sorption determined at other shaking periods. Adsorption maximum and P sorption capacity were significantly correlated negatively with pH and positively with exchangeable acidity and exchangeable and citrate-dithionite oxides of Al and Fe, while clay, organic matter and Bray's P1 available P were not significantly correlated.