Abstract
Phosphate sorption isotherms for Typic Haplorthox and Plinthaqualf soils from six sites associated with oil palm trials in the Solomon Islands were determined and are presented at Temkin plots. Clay mineralogy, pH, organic carbon, exchangeable acidity, cation exchange capacity, extractable phosphorus and extractable iron and aluminium (by both oxalate and citrate-dithlonite extraction) were also determined. Fertiliser predictions based on the amounts of phosphate sorbed by topsoils at an equilibrium concentration of 0.1 ppm of phosphorus are in general accord with vegetative responses to phosphate applications at the trial sites. Iron extracted with citrate-dithionite solutions from all soils showed a significant correlation with corresponding Isotherm slopes, which are related to the phosphate buffering capacities of soils.
