DRYLAND LUCERNE RESPONSES TO ELEMENTAL SULFUR 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 100 0-2000 mu m), screened S (a product with a range of particle sizes), a nd 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 a pplication. 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 with in 1 year of application and are best suited to annual applications; p articles of 250-500 mu m were oxidised over about 3 years, and were su ited to biennial or triennial application; particles of 1000-2000 mu m were very slowly oxidised and were not recommended as fertilisers. Sc reened S was broadly comparable with 250-500 mu m elemental S. Gypsum was an effective fertiliser form for lucerne in this environment. S in puts required for maintenance of both lucerne pasture production under a cut and removal (haying) management, and soil sulphate reserves, we re about 25 kg S/ha per year in an available form.