Pasture management in semiarid tropical woodlands: improving the herbage quality of stylos and grasses

The impacts of season and pasture management ( tree killing, superphosphate application, stocking rate) on the herbage quality of stylos and grasses were measured at Hillgrove and Cardigan, north-east Queensland. Plucked samples of Verano, Seca and buffel grass ( both sites) and a native grass ( spear grass at Cardigan and desert blue grass at Hillgrove) were collected over a 4-year period and concentrations of nitrogen, phosphorus and sulfur and in vitro digestibility were measured. There were large seasonal variations in herbage quality of all species with high quality in the early growing season and low quality in dry periods. The stylos had higher nitrogen concentrations and in vitro digestibilities than the grasses, buffel grass had a higher phosphorus concentration than the other species and there were no consistent differences in sulfur concentration between species. Buffel grass generally had higher nitrogen and phosphorus concentrations and in vitro digestibility than the native grasses. Management had relatively minor impacts but where differences did occur, herbage quality was higher in plots with live trees than where trees were killed, on plots where superphosphate was applied compared with plots without fertiliser and was greater at high stocking rate. Oversowing native pastures with stylos had no effect on the herbage quality of desert blue grass which had similar quality in oversown pasture and native pasture.