M. HIRATA

Grassland and Animal Production Division, Faculty of Agriculture, Miyazaki University, Miyazaki, Japan

Abstract

Herbage availability and utilisation at a scale of small patches (approximately a feeding station scale) were investigated in a bahia grass (Paspalum notatum) pasture under cattle grazing. For 11 grazing periods (2–7 days) between May (late spring) and October (autumn) in 2 years, pre- and post-grazing herbage masses and rate of defoliation were non-destructively estimated with an electronic capacitance probe at 182 fixed locations (50 cm × 50 cm) along 2 permanent line transects.
Distribution of herbage mass was spatially heterogeneous both before and after grazing, exhibiting patches with different herbage masses. Spatial variation in herbage mass always increased with grazing, with the increase being greater under higher mean herbage utilisation over the transects, i.e. under higher grazing intensity. Herbage consumption by animals also varied spatially with rates of defoliation differing among patches. Rate of defoliation across the locations became more uniform as the mean herbage utilisation increased, i.e. animals consumed more uniform amounts of herbage from patches under higher grazing intensity. The correlation coefficient between the rate of defoliation and pre-grazing herbage mass increased as mean herbage utilisation increased, i.e. the tendency for animals to consume more herbage from patches with higher herbage mass became stronger under higher grazing intensity. Thus, higher grazing intensity resulted in more uniform utilisation of patches by reducing selectivity by animals, but resulted in more variation in vegetation across the patches.