The dynamics of Heteropogon contortus and Stylosanthes scabra cv. Seca populations were studied in a subset of treatments in an extensive grazing study conducted in central Queensland between 1988 and 2001. These treatments were 4 stocking rates in native pasture and 2 of these stocking rates in legume oversown and supplement/spring burning treatments. For the 1999–2000 summer, population data for H. contortus in 5 of these native pasture and supplement/burning treatments were compared with those for an additional burnt treatment. Seasonal rainfall throughout this study was below the long-term mean and mean annual pasture utilisation ranged from 24 to 61%. Increasing stocking rate from 5 to 2 ha/steer in native pasture reduced H. contortus plant density. Increasing stocking rate reduced seedling recruitment as a result of its effect on soil seedbanks. Seedling recruitment was the major determinant of change in plant density, although some individual H. contortus plants did survive throughout the study. Burning in spring 1999, particularly at light stocking rate, promoted seedling recruitment above that in both unburnt native and legume oversown pasture and resulted in increased H. contortus plant density. In the legume oversown treatments, S. scabra cv. Seca density increased rapidly from 15 plants/m2 in 1988 to 140 plants/m2 in 2001 following a lag phase between 1988 and 1993. This increased S. scabra density was associated with an eventual decline in H. contortus plant density through reduced seedling recruitment. It was concluded that H. contortus population density is sustainable at stocking rates of 4 and 5 ha/steer (30% pasture utilisation) and that spring burning at light stocking rate can promote H. contortus populations. Increasing densities of S. scabra need to be managed to prevent its dominance.

An extensive grazing study was conducted between 1988 and 2001 in a Heteropogon contortus (black speargrass) pasture in central Queensland. The study was designed to measure the effects of stocking rate on native pasture, native pasture with legume oversown, and native pasture with animal diet supplement/spring burning on pasture and animal production. Summer rainfall throughout the study was below the long-term mean. Mean annual pasture utilisation ranged from 13% at 8 ha/steer up to 61% at 2 ha/steer. Increasing stocking rate treatments reduced total pasture yields while total yields in legume oversown treatments were similar to those in native pasture at the same stocking rate. When spring burning was possible, total yields were reduced in the subsequent autumn. Increasing stocking rate in native pasture tended to reduce H. contortus and Bothriochloa bladhii, increased the composition of intermediate species, such as B. decipiens and Chloris divaricata, and also changed the frequencies of a range of minor species. Oversowing legumes resulted in Stylosanthes scabra cv. Seca increasing from <1% of pasture composition in 1988 to 50% in 2000 and was associated with a reduction in H. contortus and changes in the frequencies of some minor species. Stocking rates heavier than 4 ha/steer resulted in annual pasture utilisation greater than 30% and were unsustainable because they reduced total yield and resulted in undesirable changes in species composition. It was concluded that pasture production was sustainable when stocking rates were maintained at 4 ha/steer, which equates to 30% annual pasture utilisation, and through the judicious use of spring burning.

Steer liveweight gains were measured in an extensive grazing study conducted in a Heteropogon contortus (black speargrass) pasture in central Queensland between 1988 and 2001. Treatments included a range of stocking rates in native pastures, legume-oversown native pasture and animal diet supplement/spring‐burning pastures. Seasonal rainfall throughout this study was below the long-term mean. Mean annual pasture utilisation ranged from 13 to 61%. Annual liveweight gains per head in native pasture were highly variable among years and ranged from a low of 43 kg/steer at 2 ha/steer to a high of 182 kg/steer at 8 ha/steer. Annual liveweight gains were consistently highest at light stocking and decreased with increasing stocking rate. Annual liveweight gain per hectare increased linearly with stocking rate. These stocking rate trends were also evident in legume-oversown pastures although both the intercept and slope of the regressions for legume-oversown pastures were higher than that for native pasture. The highest annual liveweight gain for legume-oversown pasture was 221 kg/steer at 4 ha/steer. After 13 years, annual liveweight gain per unit area occurred at the heaviest stocking rate despite deleterious changes in the pasture. Across all years, the annual liveweight advantage for legume-oversown pastures was 37 kg/steer. Compared with native pasture, changes in annual liveweight gain with burning were variable. It was concluded that cattle productivity is sustainable when stocking rates are maintained at 4 ha/steer or lighter (equivalent to a utilisation rate around 30%). Although steer liveweight gain occurred at all stocking rates and economic returns were highest at heaviest stocking rates, stocking rates heavier than 4 ha/steer are unsustainable because of their long-term impact on pasture productivity.

A grazing study commenced in 1988 at Calliope, Central Queensland, measured the effects of stocking rate, legume over-sowing and animal diet supplements/burning on pasture and animal production in a native black speargrass (Heteropogon contortus) pasture. This paper reflects on changes in yield and pasture composition between 1988 and 1996, during which time the seasonal rainfall was below average. At the pasture community scale, the highest stocking rate of 1 steer/2 ha reduced pasture yield but had little impact on pasture composition. The frequency of H. contortus showed no clear differences due to stocking rate although there was a slight overall trend for it to decline with time. The frequency of increaser species such asChloris divaricata was highest at the highest stocking rate. At the individual plant scale, the density of H. contortus plants declined at high stocking rate. The proportion of the sown legume Stylosanthes scabra cv. Seca increased with time reaching a density of 15 plants/m 2 and contributing 33% to the total yield in the legume treatments. Burning has reduced the occurrence of H. contortus compared with that in unburnt native pasture and this may be due to the stocking rates being too high following the fire. These results indicate the stability of pasture composition across a 4-fold range of stocking rates from 1988 to 1996. This study needs to continue, at least through a period of above average rainfall, to determine further effects of stocking rate and pasture type on pasture composition.