Quantification of the soil-water balance under different veld condition classes in a semi-arid climate

Abstract

The monthly herbage production, water-use efficiency (WUE: above-ground phytomass production per unit of evapotranspiration), surface runoff and soil loss were determined on grassland in three different ecological conditions, viz. poor, moderate and good, over a four year (1995/1996 to 1998/1999) period. In addition the same measurements were also made on an undisturbed bare soil surface and a soil cultivated twice per annum, only for the last four years. Herbage production and water-use efficiency decreased (P<0.01) when plant cover was reduced or grassland and soil condition declined. The effect of rainfall on productivity is enhanced as plant composition improves from poor through moderate to good. The highest seasonal WUE of 4.76 kg ha⁻¹ mm⁻¹ occurred in grassland in good condition. The dense plant cover of grassland in good condition provides a situation in which surface runoff and soil loss are lower (P<0.01) than that from grassland in poor condition. Direct evaporation from the bare uncultivated soil surface was on average 69% of the rainfall. These monthly production and water-use efficiency results are of the few, if not the only, data available for the semi-arid climates of southern Africa and can be used with great success in future fodder flow planning.