Factors influencing pasture utilisation in northern Australian rangelands

Annual pasture growth and utilisation were retrospectively modelled using the biophysical GRASP model for 20 pre-existing breeder herd datasets from across northern Australia as part of a broader study to quantify the effect of pasture utilisation rates on the reproductive performance of extensive beef breeding females. Annual pasture utilisation was more influenced by variation in stocking rate in the central and northern Northern Territory (NT) regions, while variation in pasture growth explained more of the variability in pasture utilisation in the Southern NT and north eastern (NE) Queensland regions. In the Alice Springs region, median pasture utilisation was 1.8 x higher than recommended levels on commercial stations compared to the utilisation rate on the research station where it was 0.7 x recommended levels, despite higher relative rainfall for the commercial herd studies. In contrast, in the Barkly the median utilisation on commercial stations was lower than recommended levels (0.7 x recommended) possibly reflecting the high relative rainfall during those studies. On commercial stations in northern NT and NE Queensland regions, median utilisation was 1.2 and 1.3 respectively x recommended levels, but this was for years with rainfall 1.6 and 1.7 times the long-term median respectively.