7.9.1 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, and can even help to store carbon which can contribute to climate change mitigation, but human activity is altering their character and quality. Farming can maintain and improve soil quality but certain practises are particularly damaging to soil structure, for example late harvested crops such as potatoes and maize. Of particular concern is damage to soil structure where soils are compacted leading to increased runoff and soil erosion.
7.9.2 Poor soil structure leads to an inability of crops and soil to make best use of manure and fertilisers. Large areas of the South West’s soils are vulnerable to becoming capped and sealed by heavy rain and to becoming compacted by inappropriate land work. This can cause flooding or water pollution as sediment and pollutants enter rivers, affecting habitats, salmon spawning grounds and other aquatic wildlife.
7.9.3 Soil wetness 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, are wet for long periods and are susceptible to compaction and run-off. Light sandy soils though more freely draining, are more prone to erosion during heavy rain and if over cultivated, cause capping of the soil which reduces water penetration and crop emergence.
Figure 7.9.1 Broad soil landscapes and their inherent risk of enhanced run-off due to agriculture
7.9.4 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% 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
7.9.5 Soil structural degradation varies greatly between landscapes, with some landscapes being particularly vulnerable and some relatively resilient to land management practises. Those with the most damage 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 7.9.2 Soil degradation within broad soil landscapes in the South West, 2002 - 2008