The replenishment of soil inorganic S and N from soil organic sources by the process of mineralisation is a major process that determines the capacity of the soil to supply S and N to plants. Rates of net S mineralisation in coarse-textured soils in Western Australia ranged from −4 to 14 kg S ha⁻¹ over the growing season (May to November), while rates of net N mineralisation ranged from 29 to 130 kg N ha⁻¹ over the same period. The low rates of net S and N mineralisation show that the application of S and N fertiliser is required to avoid S and N deficiency in cereal and canola crops. Net S immobilisation occurred when the level of soil S was greater than 5 kg S ha⁻¹, and net S mineralisation occurred when the level of soil S was less than 3 kg S ha⁻¹, When the level of soil S ranged between 3 and 5 kg S ha⁻¹, mineralised S was related to soil organic C, labile C and total S content. Hence, mineralised S appeared to occur by both biochemical and biological S mineralisation. In contrast, N mineralisation was independent of the level of inorganic soil N content and related to the level of soil organic C, labile C and total N content.