Grazing effects on soil physical properties and the consequences for pastures: a review

Grazing animals exert pressure on the ground comparable to that of agricult ural machinery. As a result, soil under pasture can be compacted. In grazin g systems based on permanent pastures or rangelands, there is little opport unity to ameliorate poor soil physical conditions through tillage. Hence, i t is important to understand the effects of grazing on soil physical proper ties and the consequent effects of these properties on pasture growth and c omposition. Most soils under grazed pasture, even those managed to minimise soil physic al degradation, will be compacted to some extent. However, the magnitude of this compaction is usually small, and limited to the upper 50-150 mm of th e soil. Compaction to greater depth, and other changes in soil physical pro perties, are more likely in recently tilled or wet soils. The response of pasture to the poorer soil conditions caused by grazing is difficult to determine, but it is likely to be small compared with the defo liation effects of grazing. Maintenance of a vigorous pasture should be a m ajor aim of grazing management and would also achieve the secondary aim of maintaining acceptable soil physical conditions.