Spatial variations in plant nutrient concentrations in tissue of a grass species as influenced by grazing intensity in a confined savannah rangeland

Abstract

Grazing can influence spatial variations in grass tissue concentrations of plant nutrients by promoting nutrient recycling through grazer dung. This study demonstrates the acuteness of the spatial variations, in a confined semiarid savannah rangeland where grazer migration has been curtailed. Eragrostis lehmanniana, a commonly grazed grass species, was selected for the study due to its abundance. Grass tissue and soil samples were collected at widely distributed sampling sites. The sample concentrations of macronutrients (N, P, K, Ca, Mg) and the micronutrients Fe, Zn, Mn, Cu, Ni, B, Mo were determined in the laboratory. Geostatistical analysis, spatial interpolation, factor analysis and Normalised Difference Vegetation Index values from a satellite image enabled assessment of spatial patterns in relation to grazing intensity. A grazing intensity induced zone of high nutrient concentrations in E. lehmanniana tissue was evident, in the vicinity of artificial water holes. Wide zones (1–2.8 km) of spatial autocorrelation in the grass tissue concentrations of all nutrients suggested grazing-induced homogeneity. Since heterogeneity is the more desirable ecosystem attribute on savannah rangelands, proactive rangeland management to promote heterogeneity is recommended. Artificial water holes need to be rotated and be more than 2.6 kilometres apart on the rangeland landscape.