Theme 1-2: Rangeland/Grassland Ecology--Poster Sessions
Description
High grazing intensity can accelerate the recycling of animal nutrients on savannah rangelands through the deposition of dung and, subsequently, nutrient mineralisation, uptake and concentration in grass tissue. The actual magnitude of this influence can vary depending on the grazing system. This study derived grazing system-dependent magnitudes of the influence of grazing intensity on concentrations of major (N, P, K, Ca, Mg, Na) and trace (B, Co, Cu, Cr, Fe, Mn, Mo, Ni, Se, Zn) animal nutrients in above ground grass tissue. Two grass species were examined: Brachiaria nigropedata, a decreaser, and Eragrostis lehmanniana, an increaser. For the species, leaf, stem and flower samples were collected in close proximity from respective sampling points in wildlife and livestock grazing sites, and a no-grazing control site. Sampling was conducted at the end of the rainy season in the semi-arid savannah rangelands of north-western South Africa. The concentrations of the nutrients were determined in the laboratory using standard methods. B. nigropedata had higher nutrient concentrations than E. lehmanniana. Samples from high grazing intensity sites had higher nutrient concentrations than the control site, an effect more pronounced in B. nigropedata. Such sites also had low grass cover, a characteristic of grazing lawns. They included the open access communal rangelands and the vicinity of artificial water holes. The two species manifested inter-site covariance in nutrient concentrations, indicating that sites under high grazing intensity generally had high nutrient concentrations in grass tissue, and vice versa. The short, nutrient-rich grass in grazing lawns is attractive to grazers, which can widen the lawns by perpetuating high grazing intensity and low grass biomass. However, not all grazers are adapted to grazing short lawn grass, which can have implications on grazer diversity. The study concludes that grazing-induced increase in nutrient concentrations in grass tissue manifests more in inherently high-nutrient species.
Included in
Influence of Grazing Intensity on Nutrient Concentrations in Grass Tissue: Evidence from Two Savannah Grass Species
High grazing intensity can accelerate the recycling of animal nutrients on savannah rangelands through the deposition of dung and, subsequently, nutrient mineralisation, uptake and concentration in grass tissue. The actual magnitude of this influence can vary depending on the grazing system. This study derived grazing system-dependent magnitudes of the influence of grazing intensity on concentrations of major (N, P, K, Ca, Mg, Na) and trace (B, Co, Cu, Cr, Fe, Mn, Mo, Ni, Se, Zn) animal nutrients in above ground grass tissue. Two grass species were examined: Brachiaria nigropedata, a decreaser, and Eragrostis lehmanniana, an increaser. For the species, leaf, stem and flower samples were collected in close proximity from respective sampling points in wildlife and livestock grazing sites, and a no-grazing control site. Sampling was conducted at the end of the rainy season in the semi-arid savannah rangelands of north-western South Africa. The concentrations of the nutrients were determined in the laboratory using standard methods. B. nigropedata had higher nutrient concentrations than E. lehmanniana. Samples from high grazing intensity sites had higher nutrient concentrations than the control site, an effect more pronounced in B. nigropedata. Such sites also had low grass cover, a characteristic of grazing lawns. They included the open access communal rangelands and the vicinity of artificial water holes. The two species manifested inter-site covariance in nutrient concentrations, indicating that sites under high grazing intensity generally had high nutrient concentrations in grass tissue, and vice versa. The short, nutrient-rich grass in grazing lawns is attractive to grazers, which can widen the lawns by perpetuating high grazing intensity and low grass biomass. However, not all grazers are adapted to grazing short lawn grass, which can have implications on grazer diversity. The study concludes that grazing-induced increase in nutrient concentrations in grass tissue manifests more in inherently high-nutrient species.
