Sulfur dynamics in sub-tropical soils of Australia as influenced by long-term cultivation

Deficiencies of S in agricultural crops are becoming more common but comparatively little is known regarding the kinetics of cultivation-induced long-term changes in soil S pools. In the present study, six soils were examined with samples collected from 82 sites - this allowing examination of the effects of cultivation for up to 70 years. For four of the six soils, long-term cultivation resulted in significant decreases in total S concentrations, with calculated decreases ranging from 35 to 51 %. This decrease was due to mineralization of organic S, with half-life values ranging from 1.0 to 11 years. Generally, organic S decreased linearly with organic C concentrations. For newly-cultivated soils, the mineralization of organic S was sufficient to replace the S harvested in wheat (Triticum aestivum) grain, but after prolonged cultivation, the rate of S mineralization decreased by several orders of magnitude. The data presented here provide important information on the effects of cultivation on S dynamics within sub-tropical soils - this being required to effectively and sustainably manage these systems.