Department of Plant Sciences

Reductions in atmospheric inputs of S in rainfall, and the world's reliance on non-, or low-S containing TSP, DAP, MAP and urea has resulted in a widening gap in the S input/output balance, and an increasing incidence of S deficiency in agriculture.

A technology (“Thiogro”) to incorporate elemental S, with or without sulphate S, into phosphatic fertilizers has been developed and patented by Shell. The fertilizers produced by this process are generically called "Sulphur Enhanced Fertilizer" (SEF). The technology to produce these fertilizers results in microfine particles of elemental S being distributed throughout the fertilizer granule and the process can be safely and economically retrofitted to most existing ammonium phosphate and TSP fertilizer plants.

A wide range of experimental N, P, S formulations have been made, with elemental S concentrations up to 15%. Controlled environment and glasshouse studies, with and without 35S as a tracer, have shown that S oxidation readily occurs. Agronomic testing of several of these products has been undertaken in pastures and in a wide range of crops in temperate and tropical environments. Of the 136 experiments conducted 84 were responsive to S and these generating a weighted mean crop yield increase to SEF of 14%, compared to the zero S control.

SEF technology allows the incorporation of S into fertilizers in a safe and economical way and the increased yields resulting from their application to S responsive soils has resulted in improved utilization of the other nutrients applied in the fertilizer.