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 basis for setting realistic SOC targets across different land uses and soil types than SOC concentration alone. Using two decades of data from the National Soil Inventory of England and Wales plus long-term field experiments, the authors propose differentiated SOC/clay targets for arable (1/13), ley grass (1/10) and permanent grass and woodland soils (>1/8). The findings suggest these targets are broadly applicable across similar temperate regions globally and at national to sub-regional scales.

UK applicability

These findings derive directly from UK National Soil Inventory data and long-term field experiments conducted in England, making them directly applicable to UK soil management policy and practice. The proposed SOC/clay targets can inform national and devolved soil health targets and land management guidance, particularly for arable and grassland systems across England and Wales.

Key measures

Soil organic carbon (SOC) concentration; SOC/clay ratio; changes in SOC and SOC/clay between two National Soil Inventory samplings (1978–1983 and 1994–2003); long-term field experiments under ley-arable rotations

Outcomes reported

The study compared changes in soil organic carbon (SOC) and SOC/clay ratios over time (1978–2003) across arable, grassland and woodland soils in England and Wales, and evaluated the use of SOC/clay ratio normalisation as a more meaningful metric than SOC alone for setting realistic targets by land use. The research identified that nearly half of arable soils had degraded SOC/clay ratios whilst soils with initially high ratios experienced greater SOC losses, and proposed differentiated long-term targets for arable, ley grass, permanent grass and woodland soils.

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