Grass-white clover relationships during pasture development. 2. Effect of nitrogen fertilizer with superphosphate

Abstract

The development of an intermittently grazed phalaris-white clover pasture was studied from 1967 to 1970 following factorial annual applications of nitrogen fertilizer (0, 56, 11 2 kg N ha-1) and superphosphate (0, 188, 375 kg ha-1) onto a previously unfertilized site near Armidale, New South Wales. Each year superphosphate increased annual yields of phalaris, clover and total pasture. The response to superphosphate of phalaris was mainly linear, but in the final year of the experiment the yield of clover was greater at the intermediate rate (SP188) than at SP375. Nitrogen increased annual dry matter yields of phalaris and total pasture only in the presence of superphosphate. Clover growth was not suppressed by nitrogen fertilizer until the final year, when total pasture yields were not increased by nitrogen. In the absence of applied nitrogen, pastures on the SP375 treatment were clover-dominant in 1967 and 1968 but strongly grass-dominant in 1970; at SP188, pastures remained clover-dominant after the establishment year. The application of up to 112 kg N ha-1 year -1 reduced the intensity of the clover-dominant phase at SP, and circumvented clover-dominance at SP188. Grass-white clover relationships during pasture development are discussed in relation to the prevention of cattle bloat.