Preventing compaction

Compaction occurs when a force compresses the soil and pushes air and water out of it so that it becomes more dense. Platy aggregates form and the soil tends to crack horizontally rather than vertically.  Compaction is more severe when the soil is wet and less able to withstand compression.

The most likely causes of compaction in any situation should be identified and managed carefully. In some situations, damage cannot be avoided completely, but it is important that the risk is noted and the impacts investigated.

In grassland systems the two main causes of compaction are

Naturally soil structure is formed and then maintained through a range of physical processes (e.g. wetting-drying cycles, freeze-thaw) and biological interactions (e.g. plant roots and other ‘ecosystem engineers’). Supporting the biological processes of structure formation and increasing soil organic matter content have been shown to help create resilient soil structures that can increasing bearing capacity and trafficability and allow soils to withstand damage from routine farm practices more effectively.  However, the detailed mechanisms supporting structural resilience in the soil are not yet well understood.

Reducing machinery damage

Between 50 and 80% of damage by machinery is caused by its first pass when on wet ground. 

  • If possible keep off wet fields, especially 48 hours after heavy rainfall, when surface soils are wet. 
  • If you are not sure, dig a hole and see for yourself how plastic the soil is – check the whole topsoil, even if the surface looks fine.  If the soil can make a worm when you roll it between your hands, it is too wet for trafficking.
  • Where possible reduce ground pressure by reducing machine size and total axle loads.
  • Reduce ground pressure with larger tyres and lower inflation pressures
  • Control your trafficking on a field – use established wheelings, especially with heavy loads e.g. silage trailers.

Reducing compaction from livestock

Compaction by livestock is strongly linked to livestock density.

The risk of compaction is much higher with wet soil and low plant density – hence in situ grazing of forage crops is particularly risky.  Vegetation cushions the soil on top, while the plant roots maintain soil structure underneath.

  • The wetter the soil becomes the greater the potential for damage by grazing.  Keep livestock out of wet fields (or fence off wet areas within fields).  If you are not sure, check how big the risk of damage is.
  • In some seasons you may need to create a sacrifice area, accepting poor grass performance next season, but knowing that the most important/productive pastures have been protected.
  • Outwinter only on light, free-draining, well structured soils.
  • Use strip grazing and back fence stock.
  • More frequent grazing rotations reduces potential compaction.
  • Use farm tracks to move animals across fields
  • Move drinking troughs and feeders regularly in wet conditions. Feed using a mobile snacker system rather than fixed troughs It may be more work in the short-term but the long-term benefits are high.
  • Minimise traffic into fields by storing bales close to where they will be fed

Allow at least two weeks before grazing after slitting and sward lifting operations