PHOSPHORUS AND BEEF-PRODUCTION IN NORTHERN AUSTRALIA .8. THE STATUS AND MANAGEMENT OF SOIL-PHOSPHORUS IN RELATION TO BEEF-PRODUCTION

This paper examines relations between pasture and dietary attributes and liveweight gain (LWG) with bicarbonate extractable soil P (P(B)) in the surface 10 cm soil from grazing experiments at 4 sites in northern Australia. The grazing experiments focused on the role of P as a fertilizer or direct supplement on LWG of steers grazing grass-legume pastures. Soil P(B) was highly related to annual LWG/head across 3 of the sites but with different functions for the P supplemented and unsupplemented treatments. Similarly, soil P(B) was also highly related to plant P concentration and dietary P suggesting a causative role of soil P status on LWG. A model to estimate the residual P concentration in soil was effective in predicting the variation with time in soil P(B) due to P fertilizer addition in these pastures, despite considerable variation between sites in pasture type, climate and soil type. The use of these functions in an animal production model will assist in making decisions on the utilization and development of low P soils for beef production.