Treading (Pugging) and Compaction of Pasture Soils
Nature and effects of treading
The incidence of treading damage is related to factors such as rainfall, soil properties and grazing intensity. It occurs when the soil is so soft that the hooves of grazing animals cannot be supported by the surface and they press into the soil (Figure 8). In some cases, they may leave depressions up to 10 cm deep.
Figure 8: Effect of treading on compaction of the soil. Redrawn from Batey (1988)
Nature of treading effects
Treading by grazing animals can have two main effects on soil physical properties:
- where soils are very wet (i.e. close to saturation), the penetration of animal hooves into the surface soil produces a "puddling effect". This involves the remoulding of surface soil with the loss of large soil pores. During this process there can also be extensive tearing and burying of pasture plants, and
- at lower soil moisture contents (i.e. around field capacity), puddling is less of a problem. However, the soil is still plastic and malleable and can be compacted by the treading of grazing animals. The depth of compaction can vary from 2 to 12 cm below the soil surface.
An important point about the effect of treading is that it tends to be a "self perpetuating" phenomenon. If a soil is partially pugged early in the winter then water will tend to remain on the surface for longer. As a result, the soil will remain softer and wetter and the hooves of grazing animals will do more damage at subsequent grazings than they would on undamaged soil.
Effects on pasture production
The consequences of treading on pasture production occur through direct damage to plants and indirectly through compacted soil conditions limiting subsequent growth.
- Crushing and bruising of leaves and stems, damage to roots and burial of plants in the mud can cause a direct and significant reduction in subsequent pasture yield.
- Compaction reduces the volume of large pores in the soil, thus restricting the movement of water into the subsoil. This increases the soil’s susceptibility to waterlogging and anaerobic conditions, which can restrict plant root growth. In addition, compaction increases mechanical resistance to root growth. As a result of these factors, pasture production can be reduced.
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