Rock phosphate and superphosphate as sources of phosphorus for subterranean clover on an acid sandy soil

Abstract

Subterranean clover was grown on an acid sandy soil in a field experiment at Mount Compass, South Australia, where the mean annual rainfall is 837 mm. Rock phosphate and superphosphate were applied at 0 to 66 kg ha-1 P. Dry matter yields and phosphorus uptake by the clover and the phosphorus content of the soil were determined. At given levels of addition of phosphorus, rock phosphate was as effective as superphosphate in increasing dry matter yield and phosphorus uptake by the clover in the year of application. Rock phosphate also increased yield and uptake in subsequent years, but superphosphate had little residual effect. Leaching losses of phosphorus from the top 10 cm of soil during three and a half years were equal to 100 per cent and 80 per cent of that applied in superphosphate at 22 and 66 kg ha-1 P respectively. The corresponding losses where rock phosphate was applied were 80 per cent and 60 per cent. Most of the phosphorus leached from superphosphate was lost within two months of the application.