Structural condition of agricultural soils in the UK

The maintenance of good soil structure is central to the delivery of resilient and economically productive cropping systems, due to its influence on crop root proliferation (and hence water and nutrient use efficiency) and the movement of air and water through soils. Indeed, poorly structured and compacted soils are often associated with lower crop yields, higher inputs (nutrients, energy) and an increased risk of flooding, run-off and erosion, leading to soil and nutrient losses to watercourses.

Regular monitoring of soil structural condition is vital at the field level to inform soil management decisions. The most effective and practical method for determining soil structure is the direct visual and physical examination of the soil profile. There has been considerable development of semi-quantitative visual soil evaluation techniques (e.g. Visual Soil Assessment – VSA or Visual Evaluation of Soil Structure – VESS) as low cost, but effective field methods to assess soil condition. Rather than measuring one specific property, these methods provide an overall, three dimensional assessment of soil structural condition and are useful for detecting the nature and extent of any soil structural damage.

A number of recent surveys of arable, horticultural and grassland soils have used visual soil evaluation methodologies. These surveys not only give a snapshot of the current condition of soils in the UK but also enable the identification of those soil types, regions and practices that are most vulnerable or at risk to degradation, and to which efforts to protect or improve soils can be targeted. Although there was some variance between surveys (most probably due to where and when they were conducted and hence soil wetness), the results suggest an estimated 40-60% of agricultural soils in the UK are in moderate condition (i.e. show evidence of some structural degradation due to the presence of coarse, angular aggregates with low porosity); and up to 30% in poor condition (or severely degraded; i.e. soils dominated by coarse, firm angular or platy aggregates, with low porosity and roots confined to cracks) depending on the year, sector and region. Furthermore, it is clear that traffic and tillage pans (compacted layers) are widespread within arable and horticultural systems.

Soil management should include methods to improve soil resilience (e.g. by improving soil organic matter levels), avoid or limit damage (e.g. using low ground pressure tyres or controlling traffic) and to alleviate severe compaction where it occurs (typically by cultivation using subsoilers/sward lifters). However, a recent survey indicated that cultivations are often not matched to soil conditions and the depth and nature of compacted layers. Effective soil structural assessments that quantify the impact of recent cultivation operations and link findings to management options will help improve soil structure, crop productivity and business profitability.