Phosphorus adsorption by surface samples of five ironpan soils of Ghana

Phosphorus adsorption by surface samples of five ironpan soils (Kumayili, Kpelesawgu, Nyankpala, Wenchi and Changnalili series) within the Guinea Savannah zone of Ghana were studied. The samples differed in their capacity to adsorb added inorganic P. Per cent adsorbed P decreased as P additions and equilibrium P concentrations increased. P adsorption isotherms obtained were in two parts, and approximately 25 and 40% of the total adsorption was represented by the first lower part of the Langmuir isotherm. Phosphorus adsorbed correlated with percentage organic matter, oxalate-extractable Al and dithionite-HCl-extractable Fe but not with percentage clay, pH and dithionite-citrate-extractable Fe. Fractionation following six days of equilibration showed that added inorganic P was retained mostly as Al-P rather than as Fe-P. It was found that samples of three of the ironpan soils, the Kumayili, ?Kpelesawgu and Nyankpala series, have low P adsorption capacities.