Pasture yield and composition changes in a Central Queensland black speargrass (Heteropogon contortus) pasture in relation to grazing management options

Abstract

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.

Impacts of grazing management options on pasture and animal productivity in a Heteropogon contortus (black speargrass) pasture in central Queensland. 2. Population dynamics of Heteropogon contortus and Stylosanthes scabra cv. Seca

“…This reduced H. contortus density was associated with increased S. scabra density, which was particularly rapid after 1993, while S. scabra dominated the legume oversown quadrats in 2001 with plant densities of 140 plants/m 2 . Results presented here provide further data and are consistent with earlier results from this study (Orr et al 2001).…”

“…A preliminary paper (Orr et al 2001) reported changes in the density of H. contortus in native pasture, legume oversown native pasture, and animal diet supplement/spring burnt native pasture and S. scabra cv. Seca in the legume oversown pasture between 1988 and 1996.…”

Impacts of grazing management options on pasture and animal productivity in a Heteropogon contortus (black speargrass) pasture in central Queensland. 1. Pasture yield and composition

“…Reduced total yield with increased stocking rate was apparent by the second year of treatments, although there was a longer time lag before the effects of treatments were reflected in changes in pasture composition. These findings are consistent with earlier findings from this study (Orr et al 2001), while subsequent data recordings further support the notion of the time lag impact on pasture composition change. In particular, the Orr et al (2001) paper reported no effect of heavy grazing on H. contortus, while subsequent data recordings provide evidence of a decline in H. contortus yield, particularly since 1998.…”

“…These findings are consistent with earlier findings from this study (Orr et al 2001), while subsequent data recordings further support the notion of the time lag impact on pasture composition change. In particular, the Orr et al (2001) paper reported no effect of heavy grazing on H. contortus, while subsequent data recordings provide evidence of a decline in H. contortus yield, particularly since 1998.…”

“…The study was designed to assess the long-term interactions among soil, plant, and animal parameters in relation to rainfall. A preliminary paper (Orr et al 2001) reported changes in pasture yield and composition between 1988 and 1996 and this current paper reports further changes between 1988 and 2001. Further papers in this series report the dynamics of H. contortus and Stylosanthes scabra cv.…”