USE OF POWDERED ELEMENTAL SULFUR AS A SULFUR SOURCE FOR GRASS AND CLOVER

Upland pastures on coarse-textured sulphur (S)-deficient soils in mode rate to high rainfall areas may benefit from S fertilization using ele mental 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 labo ratory incubations using an upland soil at 7 and 14 degrees C, oxidati on of the 120 mesh S was very slow while 65% of the 300 mesh S was oxi dized after 48 days at 14 degrees C. In pot trials of ryegrass in a lo wland soil and of ryegrass and clover in the upland soil both elementa l S grades gave satisfactory yield increases which were not significan tly different from applying potassium sulphate. High ambient temperatu res during the pot experiment probably ensured an adequate oxidation r ate of both elemental S grades. High application rates of the potassiu m sulphate gave rise to luxury consumption while very high rates of el emental S (equivalent to 200 kg S ha(-1)) showed some toxicity. Applic ation of a previously-described model of S oxidation confirmed the imp ortance of soil temperature in controlling S oxidation rates.