Assessment of the phosphorus and sulphur status of subterranean clover pastures. 1. Environmental factors and pasture responses

Abstract

A series of 21 standardized field experiments was set out on established subterranean clover (Trifolium subterranem) pastures in south-eastern New South Wales in the autumn of 1963. Pasture growth at eleven of the 21 sites responded to phosphorus addition ; eight responded to sulphur addition. A dual deficiency existed at five sites. Seasonal pasture production was increased by up to 3,200 lb of dry matter an acre by phosphorus addition, and by up to 5,500 lb by sulphur addition. Clover was the component responsive to phosphorus and/or sulphur at most sites. To determine whether site characteristics can provide a basis for predicting the phosphorus or sulphur status of a pasture, several climatic and soil components of the environment were correlated with responses. Phosphorus status was not related to the rainfall, temperature or elevation at the site, nor to the kind of soil or soil pH. The more deficient pastures were younger, and, on the granitic soils only, present phosphorus status reflected the amount of superphosphate used in the past. Sulphur status was significantly related to rainfall for the podzolic soils only (r = 0.72) ; the driest sites tended to be the most sulphur deficient ones. Sulphur status showed a poor overall relationship with temperature, the trend being for the occurrence of more deficient soils at lower temperatures or higher elevations. Within the podzolic soils, the relationship with temperature was more definite (r = 0.69). There was no association with kind of soil or past superphosphate use, but there was a moderate to strong relationship (r = -0.78) with soil pH (the less acid, the more S deficient).