Changes in nitrogen and sulphur content and other soil properties after application of ammonium sulphate to grazed pastures in Western Australia

Abstract

Ammonium sulphate was applied to a grazed pasture on a duplex soil for five years at annual rates of nil (N0), 280 kg ha-1(N1) and 840 kg ha-1(N3). N0 became clover dominant and N3 became grass dominant but net increase in nitrogen in the top 10 cm of soil over five years was similar on N0, N1 and N3. Fertilizer nitrogen was rapidly lost after heavy rains in autumn. On all treatments, soil accumulated inorganic nitrogen in summer. A balance sheet for sulphur could not account for 48 per cent of sulphur in the top 10 cm on N0 (superphosphate only), 82 per cent on N1 and 90 per cent on N3. Ammonium sulphate decreased pH, exchangeable calcium, magnesium and potassium (but not sodium), and cation saturation, and increased exchangeable acidity. Apart from pH, these effects were confined to the top 10 cm of soil. The results show that in a sandy-surfaced soil ammonium sulphate is an inefficient source of nitrogen and sulphur because nitrogen and sulphur are readily lost.