Soil-water utilisation and sustainability in a semi-arid grassland

Soil water balance, water use efficiency (WUE: crude protein produced per unit evapotranspiration), productivity, and soil temperature were assessed for semiarid grasslands in Bloemfontein, South Africa, during four growing seasons. Grasslands were classified as being in poor, moderate, or good condition, based on the grazing value and ecological status of their plant species composition. Good grassland had a lower percentage crude protein content than poor grassland, but a higher total crude protein content, due to the greater plant biomass produced by good grassland. Grassland degradation was accompanied by a significant decline in WUE. Soil water content was much lower in poor than in good grassland, because surface runoff was greater in the former due to sparser vegetation cover. During most months, soil temperatures measured at a 50-mm depth increased with the level of grassland degradation.