Abstract In a highly sulphate retentive soil a single dressing of 168 kg/ha S as gypsum protected pasture against all but slight S deficiency for 5 years, the total span of this experiment. From this single application dry-matter yields were as high as those obtained from four annual applications of 45 kg/ha each. Yield responses to S were strongly influenced by season (large in summer — autumn, absent in spring). High rates of gypsum helped white clover to survive in a dry summer. The ratio of rainfall, in excess of evapotranspiration, to the downward movement of the crest of the sulphate displacement wave was about 3:1 in the top 15 cm, but increased markedly with depth. In spite of 3000 mm excess rainfall in 5 years, applied sulphate did not appear to penetrate below 45 cm. Low equilibrium concentrations of inorganic sulphate in the soil solution (below 1 ppm) were associated with maximum yields. Phosphate-displaceable sulphate (PDS) in the topsoil did not correlate well with the observed S status of t...