Residual effects of sulfur fertilizers on cut swards of a Stylosanthes guianensis and native grass pasture on a euchrozem soil in north Queensland

Abstract

A field experiment was undertaken at Meadowbank Station between 1974 and 1980 to assess the residual effects of sulfur application, as gypsum and coarse elemental sulfur, on yields and composition of an established Stylosanthes guianensis cv. Graham and Themeda australis pasture. Sulfur rates ranged from 0-20 kg S ha-1 in years 2 and 3 and from 0-80 kg S ha-1 in year 4. The fertilizer was applied as a single dressing at the beginning of the growing seasons of 1975 (year 2), 1976 and 1977. Dry matter yield and concentrations of nitrogen and sulfur in the legume generally decreased to levels of unfertilized plots after two growing seasons when up to 20 kg S ha-1 was applied. With a rate of 80 kg S ha-1 at the beginning of the 1977 growing season, a response to residual sulfur was still evident in 1980. In each year when a sulfur application was made, there was a strong response by the legume component in terms of yield, legume content and concentrations of nitrogen and sulfur. Coarse elemental sulfur was generally not as effective as gypsum. Phosphate-extractable sulfur in the surface soil (0-10 cm) was low (1 -4 ¦g g-1) and did not change greatly as a result of sulfur applications up to 20 kg S ha-1. There was evidence of movement of sulfur down the soil profile in plots that received 80 kg S ha-1 as gypsum, but it was not so marked with elemental sulfur. It is suggested that an application of 40 kg S ha-1 as elemental sulfur or gypsum is sufficient to establish and maintain the legume component of the pasture for a period of 4 years.