Summary
This peer-reviewed study demonstrates that normalising soil organic carbon by clay concentration provides a more meaningful indicator of soil degradation and land-use differentiation than SOC alone. Drawing on 25 years of data from the National Soil Inventory of England and Wales plus long-term field experiments, the authors propose soil- and land-use-specific SOC/clay targets (1/13 for arable, 1/10 for ley grass, >1/8 for permanent grass and woodland) applicable across temperate regions, offering a practical framework for setting realistic carbon management objectives at national to sub-regional scales.
Regional applicability
The findings are directly applicable to United Kingdom soil management policy and practice, as they are based entirely on English and Welsh soils and land uses. The proposed SOC/clay targets can inform agri-environment schemes, soil carbon auditing, and land management guidance tailored to UK soil types and farming systems.
Key measures
Soil organic carbon to clay ratio (SOC/clay); absolute SOC concentration; changes in SOC/clay between two National Soil Inventory samplings (1978–1983 and 1994–2003); long-term field experiment data from ley-arable rotations; SOC/clay targets for arable (1/13), ley grass (1/10), permanent grass and woodland (>1/8)
Outcomes reported
The study compared changes in soil organic carbon (SOC) to clay ratios across different land uses in England and Wales between 1978–2003, and evaluated these ratios as meaningful indicators of soil degradation relative to SOC alone. It established soil-specific and land-use-specific targets for SOC/clay ratios that could guide realistic soil management goals, validated through long-term ley-arable rotation experiments on contrasting soils in the East of England.
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