SOLUBILITY OF ALUMINIUM IN SOILS OF THE HUMID TROPICS

Abstract

Summary Soil samples obtained from genetic horizons of an upland and acid sulphate soil of Sierra Leone, were equilibrated with 0.01 M CaCI using a 1:2 soil to solution ratio. Al 3+ activity was estimated from total Al measured in the equilibrium extract, by accounting for hydrolysis and the formation of other complex species. The Al 3+ activity was pH‐dependent, but the Al(OH) 3 ion product was I'airly constant throughout the upland soil profile; Al 3+ activity was near that expected for equilibrium with kaolinite and quartz. In the acid sulphate soil alunite appeared to control the activity of Al 3+ .