Changes in organic carbon to clay ratios in different soils and land uses in England and Wales over time

Summary

This study demonstrates that normalising soil organic carbon by clay concentration provides a more meaningful indicator of soil carbon status across different land uses than SOC alone. Using data from the National Soil Inventory of England and Wales and supporting long-term field experiments, the authors establish that almost half of arable soils had degraded SOC/clay ratios, compared with 5% of permanent grass and woodland soils. The research proposes evidence-based target SOC/clay ratios for arable (1/13), ley grass (1/10), and permanent grass and woodland (>1/8) soils, with applicability across temperate regions.

UK applicability

These findings and proposed target ratios were derived directly from English and Welsh soils and should be directly applicable to UK soil carbon management policy and land use monitoring. The results provide quantitative benchmarks for assessing soil health degradation and guiding carbon sequestration targets in UK arable and grassland systems.

Key measures

Soil organic carbon concentration; clay content; SOC/clay ratio; changes in SOC/clay ratio over time by land use (arable, ley grass, permanent grass, woodland)

Outcomes reported

The study compared changes in soil organic carbon (SOC) to clay ratios across different land uses in England and Wales between two national soil inventory samplings (1978–1983 and 1994–2003), and validated findings using long-term ley-arable rotation experiments. It quantified the prevalence of degraded SOC/clay ratios in arable soils and proposed realistic target ratios for different land use types.

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