Responses by pasture to current and previous application of superphosphate

Abstract

The effects of heavy initial applications and regular annual dressings of superphosphate on the winter and spring yields of herbage from a subterranean clover-annual grass pasture were measured in a four-year experiment at Rutherglen, north-eastern Victoria, Basal levels of soil phosphorus were established in 1959 by applying 1, 7, or 13 cwt (112 lb) of superphosphate an acre to an established pasture. From 1960-1963, 0 or 1 cwt of superphosphate an acre a year was applied in all factorial combinations (i.e., 0-0-0-0, 0-0-0-1, . . . . . . . . 1-1-1-1). On the plots that received 1 cwt an acre in 1959, current application of superphosphate increased winter production in every year (by 425-1230 lb dry matter an acre, or 36-362 per cent). On the plots that received 7 or 13 cwt an acre in 1959, winter responses to current dressings were small and not significant in three of the four years, indicating a strong residual effect from the basal dressings. Responses in spring were small in both absolute (maximum 290 lb dry matter an acre) and relative (4-12 per cent) terms and were not significant in three of the four years. Tn both winter and spring yields, residual effects of current dressings were small (maximum 245 lb dry matter an acre) and generally not significant.