PASTURE MANAGEMENT IN SEMIARID TROPICAL WOODLANDS - EFFECTS ON HERBAGE YIELDS AND BOTANICAL COMPOSITION

The effects of pasture management options (introduced legumes and gras ses, superphosphate, timber treatment, cultivation before sowing, stoc king rate) on the yield and botanical composition of pastures were mea sured from 1982 to 1992 at 2 sites, Hillgrove (extractable phosphorus, 50 mg P/kg) and Cardigan (extractable P, 6 mg/kg), near Charters Towe rs, northeastern Queensland. Despite generally poor establishment and growing conditions, some sown species (Stylosanthes hamata, S. scabra, Cenchrus ciliaris, Urochloa mosambicensis) established and persisted at both sites. The initial sown grass populations were small but yield s increased markedly towards the end of the experiment. There were no yield responses by the native pastures to superphosphate, but the sown pastures responded at Cardigan, although not at Hillgrove. There were large yield responses to tree killing. The percentage increase in her bage yield following tree killing increased as the available water in the soil during the growing season decreased, and was greater at the h igher fertility Hillgrove site.Overall, the native pastures were domin ated by perennial grasses, but annual grasses and forbs increased on p lots with live trees and high stocking rates towards the end of the tr ial. Sown grasses, particularly C. ciliaris, became dominant (and are likely to remain so) at Hillgrove and on plots with superphosphate at Cardigan, especially where the trees were killed. Productive, mixed pa stures with reasonable proportions of both grass and legume were maint ained under live trees.