Compaction is where soil has been squashed into a solid impermeable layer, either at the surface or within the topsoil and subsoil. Compacted layers restrict the movement of air, water and nutrients down the soil profile.
It leads to poor root growth, which stresses the plant and reduces its response to nitrogen and other nutrients. These videos give useful guidance:
What to look for
Soil can be compacted at many different levels throughout the soil profile and can be damaging at any level. Poor and shallow rooting of crops is an obvious effect of compaction. Gateways and tracks through fields are particularly vulnerable areas to compaction and care should be taken to minimise this where possible.
Measuring compaction
Dig a hole 50cm deep when the soil is not excessively wet or dry. Look how far the roots and moisture extend down the profile and look for any obvious change in the soil structure. Where the spade meets resistance is where compaction starts – this will also help identify what the cause is and whether action is required.
Using the table below as a guide, assess the compaction score of your soil. An average of the two scores gives an overall figure.
|
Indicator |
Poor (0) |
Medium (1) |
Good (2) |
|
Physical |
|||
|
Topsoil compaction (d) |
Obvious hardpan, poor rooting |
Some restrictions to penetration and root growth |
Easy penetration and good root growth |
|
Subsoil compaction (e) |
Hardpan and/or soil occurs in large compresses pieces, roots absent |
Soil occurs in medium pieces, root penetration with some difficulty |
Soil occurs in small pieces, roots penetrate without difficulty |
Soil type can have a large influence on compaction, with heavy clay soils being particularly vulnerable, while coarse, sandy soils rarely suffer from compaction.
Improving compaction
Despite variations in soil type, there are a number of measures that will minimise compaction on all soil types. Adjusting soil management practices can have a large influence on the soil quality and can particularly influence the long-term sustainability of your soil. Linking Environment And Farming (Leaf) carried out on farm soil interviews with a wide variety of farmers across the UK. Despite a large variety of soil types and farm types, many had adjusted their soil techniques in the same way to improve their soil quality. The following measures were used particularly to minimise compaction. Further information on the farm-specific implication of these changes can be found in farm case studies.
Importance of timeliness
Allowing soil conditions to dictate cultivations timing will help minimise compaction. Working wet soil is the most common cause of problems. It is sometimes impossible to avoid working wet soil while continuing to crop, but sometimes not cropping and allowing the soil to recover can be more economic over a whole rotation.
Traffic
Low-profile floatation tyres are a straightforward and often necessary precaution to minimise compaction. Using tracks on machinery further minimises compaction and can increase the cropped area. Crab wheels are often used on particularly heavy harvesting equipment. Fertiliser spreading techniques can be manipulated to minimise machinery passes and alleviate compaction.
Tramlines
Minimising the compacted areas by adhering to tramlines is another technique to help keep overall compaction to a minimum. Control traffic farming or GPS steering could be a farm-wide technique that would help keep tramlined areas to a minimum. Alternatively, adjusting tramlines every year and subsoiling them out could help spread the compaction.
Minimum tillage
Minimum tillage techniques can help minimise compaction. The reduced number of passes necessary in minimum tillage is a large contributor to this. The build-up in earthworms and in particular their casts, as a result of minimal soil disturbance, can further alleviate compaction.
Hardcore gateways
Gateways, especially in livestock fields, are liable for compaction. Hardcoreing the area is a relatively straightforward and long-term solution. Be aware of the effects of tracks through fields for feeding and the impact these can have on the soil. Minimise where possible.
Poaching
Poaching via livestock is a common cause of compaction and is difficult to alleviate in grassland. Ensure necessary movement of stock in wet conditions and consider bringing stock inside where appropriate. Consider the advantages of permanent pasture for winter grazing. One famer valued the deeper roots and denser swards in preventing the land from getting as wet.
Rolling
Rolling grassland often leads to unnecessary compaction. Consider relying on natural fissure drainage instead where possible. Using ballast rollers is another way to avoid unnecessary compaction.