Dryland lucerne responses to elemental sulphur of different particle sizes applied at different rates and frequencies in North Otago, New Zealand

Elemental sulphur (S) of three particle sizes (< 150, 250-500, and 1000-2000 mu m), screened S (a product with a range of particle sizes), and gypsum (a sulphate fertiliser) were each applied to lucerne pasture at 25, 50, 100, and 200 kg Siha in a dry inland environment. Pasture deficiencies first developed during the second year after fertiliser application. Oxidation rates of the elemental S particles were measured directly from the residual elemental S in the soil and indirectly by soil and plant S analyses. Particles < 150 mu m were 90% oxidised within 1 year of application and are best suited to annual applications; particles of 250-500 mu m were oxidised over about 3 years, and were suited to biennial or triennial application; particles of 1000-2000 mu m were very slowly oxidised and were not recommended as fertilisers. Screened S was broadly comparable with 250-500 mu m elemental S. Gypsum was an effective fertiliser form for lucerne in this environment. S inputs required for maintenance of both lucerne pasture production under a cut and removal (haying) management, and soil sulphate reserves, were about 25 kg S/ha per year in an available form.