The Soil Compaction Danger Level is HIGH
Posted: March 31, 2015
As soils thaw out after a snowy winter, soil moisture conditions are ideal to cause compaction.
Compaction experts use the term ‘plastic’ limit to determine when the soil is most sensitive to compaction. You can determine the plastic limit by using the ‘ball test’ – take a handful of soil, knead it in your hand – if you can make a ball out of it, the soil is in the ‘plastic state’ and wetter than the plastic limit and highly sensitive to compaction. Soil texture (sand/silt/clay composition of the soil) is important: You will notice that soil with high clay content tends to be in the plastic state more often than a sandy soil. Soil structure (the organization of soil particles in aggregates of different sizes with a network of pores of different dimensions) is also important – a soil with a stable soil structure is not in the plastic state as often as a soil with a weak structure. By increasing organic matter content you promote more stable soil structure. By using no-tillage the soil becomes more resistant to compaction because the stable matrix is interspersed by continuous and permanent pores. Yet it is important not to create ruts in no-till soil to avoid detrimental effects on soil function. Living roots are critical to make soil resist compaction better and bounce back from its effects. In fact, by combining no-tillage and vigorous cover crops you can make the soil more resilient to the effects of compaction. Feeding soil life is probably one of those unrecognized principles in compaction management –earthworms, for example, will bore many holes into soil and alleviate compaction. Tire configurations determine to a large extent how much surface compaction is caused – by using tires with low inflation pressures or tracks that have a large foot print, you reduce surface stress and therefore surface compaction. But it is also important to monitor axle load – once you exceed 10 tons per axle there is a great likelihood of causing subsoil compaction when the soil is in the plastic state. In this time of the year you can also take advantage of frost – when the soil is frozen is it not compactible. However, you need to determine if you do not cause compaction below the frozen layer. By taking into account the plasticity of your soil before going on it you can avoid causing problems that you will regret the rest of the year.