Effects of grazing management on the botanical composition of a lucerne pasture in south-eastern Queensland

Abstract

The influence of six grazing and three mowing treatments on the botanical composition of lucerne (Medicago sativa cv. Hunter River) pastures was studied at the end of a six-year experiment on black earth in southern Queensland. Rest intervals of 32-60 d were combined with grazing durations of 4, 8 or 16 d, or with mowing. Sheep were used for grazing at a year round rate equivalent to 20/ha. Frequency of occurrence of all species and their relative herbage yield contribution were estimated in autumn and spring of the last two years. Seventy-four species were recorded, but only 17 occurred in more than 5% of grazed quadrats. Survival of lucerne, the only sown species, was good (Leach 1979a); it occurred in about 70% of quadrats but its relative yield ranged from 8 to 75%. Chloris gayana was the principal volunteer perennial grass, especially in treatments grazed for short periods (4 d) where its frequency ranged from 26 to 49% and the corresponding relative yield totals from 26 to 33% in the final spring. The volunteer species most characteristic of particular treatments were Dichanthium spp. and Chloris virgata in autumn, and Malvastrum coromandelianum, annual Medicago spp. and Trifolium repens in spring. Grazing duration or mowing influenced botanical composition more than changes in resting interval. This mainly reflected the intensity of utilization rather than grazing duration per se. Opportunities for controlling volunteer species through grazing management will be limited by compensatory responses between species. However, management should aim to ensure adequate grazing of both the lucerne and the volunteer species.