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

Grazing animals exert pressure on the ground comparable to that of agricultural machinery. As a result, soil under pasture can be compacted. In grazing systems based on permanent pastures or rangelands, there is little opportunity to ameliorate poor soil physical conditions through tillage. Hence, it is important to understand the effects of grazing on soil physical properties and the consequent effects of these properties on pasture growth and composition. Most soils under grazed pasture, even those managed to minimise soil physical 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 the soil. Compaction to greater depth, and other changes in soil physical properties, 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 defoliation effects of grazing. Maintenance of a vigorous pasture should be a major aim of grazing management and would also achieve the secondary aim of maintaining acceptable soil physical conditions.