Comparing simple methods for measuring phosphate sorption by soils

Phosphate sorption curves were measured for 103 Western Australian soils sa mpled from farmers' fields. A measure of phosphate buffering obtained from a fitted curve was compared with indexes obtained from single-point measure ments of phosphate sorption. The single-point indexes were adjusted for the phosphate present in the sampled soils by adding the phosphate extracted b y the bicarbonate reagent to the measured sorption. Iron and aluminium extr acted by an oxalate solution were measured as indirect indexes. The single-point indexes were closely correlated with the values obtained f rom the sorption curve. Their correlation was much larger than that of indi rect measures.