Abstract:
Increased and sustained beef cattle liveweight gains were obtained during 1974-79 on improved pastures in an experiment on a solodic soil at Kogan in southern Queensland. Annual liveweight gains of almost 100 kg/ha and 160 kg/steer were obtained at a stocking rate of 0.62 steers/ha on Rhodes grass fertilized with nitrogen; Rhodes grass and medics; and Rhodes grass, medics and siratro. The latter two pastures received an initial application of hydrated lime and gypsum (HLG). Medics responded markedly to HLG and this resulted in a 54% increase in liveweight gain per hectare on the Rhodes grassmedic pasture. However, the capacity of Rhodes grass-legume pastures to sustain higher stocking rates was much less than Rhodes grass fertilized with nitrogen. Rate of liveweight gain varied seasonally. There was a marked depression in late autumn and early winter, a steady increase in spring, a minor depression in late spring and early summer, and a minor increase in late summer and early autumn. Comparison of animal production with a long term experiment at Narayen on a low-fertility soil showed similarities, except for the poor performance of siratro at Kogan in terms of productivity and persistence. The main differences in the soils (both Alfisols) were the presence of levels of exchangeable sodium exceeding 40% in the subsoil, and poorer physical properties of the Kogan soil. Although the experiment has shown potential for increased animal production from improved pastures in this environment, factors limiting sustained high production are high liveweight losses in the cool months, rainfall variability and pasture instability. Conservative pasture management is needed if improved species are to be retained in pastures on these soils.