Upland pastures on coarse‐textured sulphur (S)‐deficient soils in moderate to high rainfall areas may benefit from S fertilization using elemental S to avoid leaching losses. Two grades of elemental S, 120 and 300 mesh, were assessed as a source of S for grass and clover. In laboratory incubations using an upland soil at 7 and 14°C, oxidation of the 120 mesh S was very slow while 65% of the 300 mesh S was oxidized after 48 days at 14°C. In pot trials of ryegrass in a lowland soil and of ryegrass and clover in the upland soil both elemental S grades gave satisfactory yield increases which were not significantly different from applying potassium sulphate. High ambient temperatures during the pot experiment probably ensured an adequate oxidation rate of both elemental S grades. High application rates of the potassium sulphate gave rise to luxury consumption while very high rates of elemental S (equivalent to 200 kg S ha‐1) showed some toxicity. Application of a previously‐described model of S oxidation confirmed the importance of soil temperature in controlling S oxidation rates.