Effects of grazing, slashing and burning on Aristida ramosa and sheep productivity in northern New South Wales

Abstract

Summary. Studies were conducted on a natural pasture dominated by Aristida ramosa (wiregrass) in northern New South Wales. In each of the 4 studies, treatments were designed to reduce wiregrass presence by grazing, using stocking rates up to 12.5–15.0 dry sheep equivalents (dse/ha) in summer and autumn (1983–88), slashing (1984–86), or burning (2 studies, 1985–88; 1986–88) in spring before heavily grazing in summer–autumn. Effects of these treatments on A. ramosa dry matter yield and basal cover, Danthonia linkii (wallaby grass) basal cover, sheep liveweight change and fleeceweight were measured for the different time periods. Wool quality was determined from mid-side samples taken in 1983–85.

All treatments reduced A. ramosa dry matter yield and basal cover and increased D. linkii basal cover, compared with control plots continuously grazed at 5 dse/ha. From 1983 to 1988, A. ramosa dry matter yields in the control plots increased from about 1000 to 3500 kg/ha and its basal cover increased from 7 to 13%. In contrast, A. ramosa dry matter yields in heavily grazed, and spring burnt and heavily grazed treatments were <500 kg/ha, with basal cover levels of A. ramosa <0.3% while those of D. linkii were about 5%. Slashing before heavy grazing (1984–86) also reduced A. ramosa dry matter yields and basal cover compared with the control, but higher levels of A. ramosa (800 kg/ha dry matter, 1% basal cover) remained at the end of these studies.

Heavy grazing of wiregrass led to significant negative liveweight changes, compared with sheep in control plots. Slashing or burning of wiregrass to remove dead material and increase green leaf before grazing at high stocking rates, markedly reduced rates of liveweight decline. Both grazing at high stocking rate and slashing in spring followed by heavy grazing, significantly reduced the amount of wool grown in the spring–winter period and significantly decreased either wool fibre diameter, strength or point-of-break. In the long term, sheep in wiregrass control plots lost more weight than those in treatment plots at equivalent stocking rates. Results suggest that on-farm control strategies based on late winter or spring burning, and heavy summer grazing should reduce the presence of wiregrass in similar pasture system.