Field studies with radioactive sulphur-labelled gypsum fertiliser

Abstract

The movement of fertiliser sulphur (S), within soils belonging to the recent and yellow-brown earth soil groups, was investigated by applying 35S labelled gypsum fertiliser to several field trials. Under contrasting spring rainfall conditions. and at the same rate of S fertiliser application, a markedly different pattern of S distribution occurred on two recent soils of similar texture. Year-toyear variations in winter rainfall (hence leaching) also influenced fertiliser S movement at the sites studied. The magnitude of this effect depends to some extent on soil type. Halving the rate of fertiliser S application did not affect the depth of fertiliser S penetration on two soils of differing texture but resulted in 50% less fertiliser S in anyone soil depth investigated. A 2-month delay in fertiliser S application, in spring, resulted in less leaching losses on a sandytextured soil. Little difference occurred in the distribution of fertiliser S in a heavier-textured soil. The significance of the results is discussed in relation to the interpretation of fertiliser trial results and current fertiliser practices.