SOIL SULFUR STATUS, SULFUR FERTILIZER RESPONSES AND RAINFALL SULFUR ACCESSIONS AT TRIAL SITES IN THE NATIONAL REACTIVE PHOSPHATE ROCK PROJECT

The sulfur (S) status of the National Reactive Phosphate Rock Project trial sites was determined using 2 chemical extractants KCl-40 (0.25 m ol KCl/L heated to 40 degrees C) and MCP (0.01 mol mono-calcium phosph ate/l). There were marked differences between sites in KCl-40 extracta ble S down the soil profile. Soil profiles were classified into 4 grou ps according to the shape of the extractable S profile. KCl-40 was bet ter able to distinguish between responsive (significant at P = 0.10 on ly) and unresponsive sites than MCP. Mean S accession in rainfall over the 3 years ranged from 0.40 kg/ha.year at Jericho (site T17) in the centre of Tasmania to 20.33 kg/ha.year at Smithton (site T16) on the n orth-west coast of Tasmania. The proportion of S-responsive sites incr eased from 26% in the first year to 43, 42 and 48% in years 2, 3 and 4 respectively. Such a large proportion of S-responsive sites limits th e use of direct application of reactive phosphate rock fertiliser.