Soil & Water Management Centre

Developing & improving your soils

A guide to cutting soil compaction

Traffic from farm machinery is one of the main causes of compaction, which occurs whenever the ground pressure on the soil is greater than its ability to resist.

Compressing soil particles together too tightly seriously reduces the spaces between them, restricting the movement of water, nutrients, roots and earthworms as well as excluding the air vital for healthy soil micro-flora and fauna (See figure alongside)

Soil compaction is estimated to cost UK farming around £400-500 million every year:

  • Cutting crop yields by 10-15%;
  • Increasing tillage energy, time and costs by up to 300%;
  • Reducing soil water infiltration to almost zero; and,
  • Exacerbating problems of run-off and flooding.
More compaction problems are hardly surprising given the very much greater soil pressures being exerted on soils by modern farming operations (see illustration below) not to mention the need to work soils more rapidly, often under less-than-ideal conditions.

The risk of compaction depends on soil conditions 

  • Clayey and sandy soils are the most vulnerable to damage.
  • Wet conditions invariably increase the likelihood of compaction.
  • Hard, dry soils are also at risk because too much energy is required to work them.
  • Higher levels of organic matter make soils more resistant to damage.
  • Well-structured soils are also more resilient, especially under no till regimes.
 Compaction problems are often most acute on headlands given the additional load placed on the soil by heavy equipment turning, with tyres and tracks scrubbing the soil surface.

While compaction creates serious problems, soils that are too loose can also be highly problematic because they are especially vulnerable to re-compaction.

Minimising Compaction

Most compaction problems stem from a lack of understanding of soils together with insufficient care and attention during trafficking and with soil working in particular.
Reductions in soil porosity caused by traffic have been found to substantially reduce water infiltration rate, as illustrated below (Chyba, 2012).

The first pass, particularly on deeply cultivated soils, causes the greatest reduction in infiltration rate.

Work Soils with Care

Wherever possible, soils should not be worked with heavy equipment when they are at particular risk of compaction.

The soil’s load bearing capacity can be assessed prior to operations with a simple screwdriver test as shown here.

Figures showing how water movement and root growth can be restricted

Soil structure can vary from one point in a field to the next, as illustrated below

Compact and dense (above) and more favourable (below)

The most frequent causes of damaging compaction in modern arable practice are:

  • Excessive axle loads and tyre pressures
  • Excessive wheel slip
  • Travelling on soils that are too wet
  • Cultivating under extremes of wetness and dryness
  • Too many passes in the same tracks (unless using CTF)
  • Too much trafficking across the field