Superphosphate on perennial pastures. II.* Effects of a pasture response on steer beef production

Abstract

For a 3 year period, superphosphate was applied annually at rates of 0, 62, 125 and 250 kg ha-1 to an established phalaris (Phalaris aquatica)/subterranean clover (Trifolium subterraneum) pasture with a substantial history of superphosphate use. Steers, replaced annually, continuously grazed these pastures so that plant growth responses to superphosphate could be calibrated in animal production and economic terms. Pasture growth rate responses to superphosphate, relative to unfertilized treatments and averaged over 3 years, were 64, 108 and 136% for the 62, 125 and 250 kg ha-1 treatments respectively. Similar proportions of phalaris and subterranean clover were maintained in the unfertilized pasture, and phalaris became the dominant component in the fertilized pastures. Superphosphate significantly increased the level of available pasture and steer growth rates. Steers from the 62, 125 and 250 kg ha-1 treatments averaged, at sale, 70, 98 and 117 kg heavier respectively than those from the unfertilized treatments. Over the experimental period, a twofold reduction in gross margins followed from withholding superphosphate. In contrast, its application in the second and third year led to an average fourfold and sixfold improvement respectively in gross margins. It is suggested that the use of these results to test and improve simulation models of fertilizer systems is the most effective means of establishing guidelines on which to base decisions on current fertilizer policy in other situations. __________________ * Part I, Aust. J. Agric. Res., 28: 991 (1977).