Summary
This paper validates an index for assessing soil organic matter based on the ratio of soil organic carbon to clay content, using data from the 1978–83 National Soil Inventory of England and Wales covering 3,809 sites. The authors establish threshold SOC/clay ratios (1/8, 1/10, 1/13) that indicate boundaries between 'very good', 'good', 'moderate' and 'degraded' soil structural conditions, demonstrating that land use is the primary driver of variation in this ratio. The index provides a practical, scalable tool for soil evaluation and monitoring at national and regional scales using two routinely measured soil properties.
UK applicability
The study is directly applicable to United Kingdom soil management, having been developed and validated on English and Welsh soils from the National Soil Inventory. The authors suggest the index should apply to other European soils in similar climate zones, making it particularly relevant for UK agricultural policy and soil monitoring programmes.
Key measures
Soil organic carbon (SOC) to clay ratio; SOC/clay threshold values of 1/8, 1/10 and 1/13; percentage of sites in each structural condition category; variance explained by land use, soil type, annual precipitation and soil pH
Outcomes reported
The study tested an index based on soil organic carbon (SOC) to clay ratio thresholds to assess soil structural condition across 3,809 sites in England and Wales under arable, grassland and woodland uses. The thresholds identified boundaries between 'very good', 'good', 'moderate' and 'degraded' structural conditions, with 38.2% of arable sites, 6.6% of grassland sites, and 5.6% of woodland sites classified as degraded.
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