The residual value of the phoshporus and suphur components of superphosphate on some Western Australian soils

Abstract

Field trials were established on Coolup sand on three previously fertilized pastures and on one previously virgin site. The virgin site was found to be very deficient in phosphorus, but on two of the previously fertilized pastures, omission of phosphorus for as long as three years, did not reduce yield. Responses to sulphur occurred on all sites. Soil analysis showed that soil sulphate levels were highest at the end of summer, fell to low levels in winter and spring, and rose again after the cessation of growth. Applied sulphate was rapidly removed from the soils. Glasshouse trials on forty-two soils from the coastal plain and from the Kojonup district showed that most of the soils which had been regularly fertilized with superphosphate had a high phosphorus status. Some soils, both virgin and fertilized, also had a high sulphur status ; these soils either came from a low position in the drainage system or were known to have had contact with saline water. The remainder of the soils responded to sulphur. The response was little affected by the fertilizer history but was related to the soil texture- being greatest on the light soils. It is suggested that on some soils there is scope for reducing the phosphorus application and for using slowly-available forms of sulphur.