Effect of three stocking rates on a natural grassland

Abstract

The effects of three stocking rates: HR = high (1 AU/ha), MR = medium (0,75 AU/ha) and LR = low (0,5 AU/ha) on a vegetation of a natural grassland in the southwestern region of Rio Grande do Sul, Brazil, were studied during five years. Permanent quadrats were used as sampling units and beef cows for grazing. Botanical composition, frequency and cover-abundance values for grassland species were evaluated. The frequency and cover-abundance were registered according to the Braun-Blanquet cover-abundance scale. The different stocking rates promoted deep modifications in the grassland community. The low stocking rate (LR) determined a decrease in the frequency and cover of desirable grasses with good nutritive values, and increase in the low quality grasses and undesirable species. In the MR and HR stocking rates, die good quality grasses were dominant, while the low quality ones and tie undesirable species were present at a low frequency and cover. The results show that, for these grassland communities, stocking rates ranging from 0.75 to 1 AU/ha must be used. Stocking rates of 0.5 AU/ha promoted formation of vegetation where low quality grasses and undesirable plants, and frequent cleaning operations for maintenance of the productivity of the area will be required.