Soils are an essential component of our environment. They not only provide our food but, as they store water, they can filter out potential pollutants and reduce the risk of flooding. Healthy soils are vital to a sustainable environment but human activity is altering their character and quality. Farming can maintain and improve soil quality but some agricultural practices can damage the soil. Of particular concern is damage to soil structure where soils are compacted leading to increased runoff and soil erosion.
Poor soil structure leads to an inability of crops and the soil itself to make best use of manure and fertilisers. Large areas of the region’s soils are vulnerable to being or are already capped and sealed by heavy rain and to being compacted by inappropriate land work, causing water pollution as sediment and pollutants enter rivers, affecting habitats, salmon spawning grounds and other aquatic wildlife.
South West trends
The Environment Agency has carried out research into the degradation of soil structure in the South West at over 2,500 sites in 21 catchments between 2002 and 2008. Of these sites, only 11% of sites had good soil structure throughout the soil profile, whilst almost 50% are degraded and require soil structure remediation. Of the damaged soils:
5% of sites show evidence of field-wide erosion
Over 30% have degradation features such as compaction, capping that will dramatically reduce infiltration and therefore cause runoff especially given intense and prolonged rainfall
Almost 10% of grasslands are degraded by compaction (often from overstocking) to the extent of requiring mechanical intervention to improve infiltration
Picture 5.2 South West Soils map
Soil structural degradation varies greatly between landscapes, with some landscapes being particularly vulnerable and some relatively resilient to land management practices. Soils with the most damage to soil structure are those dominated by light-textured soils (sandy, silty and light loamy soils) with almost 60% of sites showing severe of high levels of degradation enough to cause enhanced runoff. The shallow chalk and limestone soils are the least damaged with less than 14% of sites showing severe or high levels of degradation.
Figure 5.5 Soil degradation within broad soil landscapes in the South West 2002-2008
The South West’s light textured soils are by far the most degraded, with almost 60% of sites showing severe or high levels. The shallow chalk and limestone soils are the least damaged with less than 14% showing severe or high levels of degradation.
Structural improvement in these soils is needed to avoid the environmental implications of enhanced runoff, including the increased incidence of muddy surface floods and reduced water quality.
Waterlogging is one of the key indicators of soil management, as it can show periods during which the soil is best worked. Heavy clay soils, for example, compact easily and are susceptible to degradation when cultivated during wet periods so are best cultivated in autumn and spring. Light sandy soils, on the other hand can be worked more throughout the year, as they tend not to waterlog. However, they are more prone to erosion during heavy rain and if over cultivated, causing capping of the soil which reduces water penetration and crop emergence.
Certain arable crops and grassland practices are particularly damaging to soil structure, for example late harvested crops such as potatoes and maize. For many years it has been known the growing of maize can have serious environmental impact. It is heavily reliant on the herbicide atrazine, a long-lasting potential groundwater contaminant that is harmful to both humans and wildlife.
The Environment Agency is currently conducting research into how maize growing can affect soil condition in the South West. Yet to be published, this research has found that maize growing can be a major environmental problem unless very high soil management standards are maintained at establishment, harvest and during the winter following harvest. However, these risks can be reduced if simple practical measures are taken, including:
Early autumn harvesting
Carrying out a shallow cultivation to break and roughen the soil surface immediately after harvest
Sub-soiling in the autumn when conditions are suitable
Helping farmers and land owners to adapt to a changing climate. See also ‘Climate change’ and ‘Agriculture’.
Promote best practice through Catchment Sensitive Farming and Environmental Stewardship. See also ‘Agriculture’.
Soil management guidance and plans for high risk soils
Key regional strategy / plans:
Soil: a precious resource - our strategy for protecting, managing and restoring soil (Environment Agency)
Environment Agency Corporate Strategy - South West Regional Contribution (Environment Agency)