Abstract 120

Winter,WH

CSIRO Division of Tropical Crops and Pastures, Tropical Ecosystem Research Centre, Winnellie, NT 5789, Australia.

Australian-Journal-of-Experimental-Agriculture. 1988, 28: 6, 669-682; 40 ref.

Native perennial grass pastures were oversown with Stylosanthes hamata cv. Verano without fertilizer or with sub-optimal levels of superphosphate or rock phosphate at 100 kg/ha at establishment and 25 kg/ha annually. Brahman steers, 1 to 3 years old, grazed the pastures and their responses to fertilizer application and supplementation with phosphorus 0 and 10 g/daily and sulphur 0 and 3 g/day were determined over 4 years. P supplementation doubled liveweight gains during the early and late wet season periods to about 0.9 and 0.7 kg/day, respectively. Pasture fertility did not affect gains in the early wet season, but superphosphate increased the late wet season gains by about 0.1 kg/day. Small weight losses occurred in all treatments during the early dry season, which increased with steer age. Weight losses were highest during the late dry season, particularly for the older, P supplemented, steers. This response was attributed to size rather than to age or supplementation. S supplementation had no effect on liveweight gain or the pastures at any time. In unfertilized pastures, Verano increased to about 25% of the DM composition whilst pastures fertilized with superphosphate and rock phosphate became legume dominant after 2 and 3 years, respectively. Fertilizer also increased the nitrogen, P and S concentrations in the forage, particularly the Verano, with superphosphate more effective than rock phosphate. In pastures where steers were supplemented with P there was a higher proportion of the naturalized legume Alysicarpus vaginalis and a lesser quantity of forage on offer. Blood inorganic phosphate and rib cortical thickness were reliable indicators of responsiveness of steers to P supplementation when measured during, or immediately after, the period of active growth.