Hydrologic response to cattle grazing in the Ethiopian highlands

Abstract

The effect of grazing pressure on infiltration, runoff, and soil loss was studied on a natural pasture during the 1995 rainy season in the Ethiopian highlands. The study was conducted on 0.01 ha plots established on sites with 0–4% and 4–8% slopes at the International Livestock Research Institute (ILRI) Debre Zeit research station, 50 km south of Addis Ababa. The grazing regimes were: light grazing stocked at 0.6 animal-unit-months (AUM) ha −1; moderate grazing stocked at 1.8 AUM ha −1; heavy grazing stocked at 3.0 AUM ha −1; very heavy grazing stocked at 4.2 AUM ha −1; very heavy grazing on ploughed soil stocked at 4.2 AUM ha −1; and a control with no grazing. Heavy to very heavy grazing pressure significantly increased surface runoff and soil loss and reduced infiltrability of the soil. It was observed that fine textured soils were more susceptible to trampling effects than coarse textured soils, and that reduction in infiltration rates was greater on soils which had been tilled and exposed to very heavy trampling. The problems of high runoff and erosion rates on the upper slopes is likely to be exacerbated by the fact that during the rainy season higher grazing pressure is exerted on the upper than lower slopes. Sediments produced from the highlands, which form headwaters of major rivers in the region, are likely to pollute streams and lakes and pile up on bottom-lands, in stream channels, and in reservoirs. With some modifications, the plot design presented here can be used for assessing livestock impacts on natural resources on different landforms at large scales such as watersheds. How the same amount of livestock mass dispersed by different livestock species impacts on the grazing lands needs to be studied further.