Oxalate-extractable aluminum alongside carbon inputs may be a major determinant for organic carbon content in agricultural topsoils in humid continental climate

Summary

This study investigates the role of soil mineral constituents, particularly aluminium-bearing reactive phases, in protecting soil organic carbon from decomposition in arable soils under humid continental conditions. Using field samples from south-west Sweden combined with published literature data, the authors demonstrate that oxalate-extractable aluminium is a stronger determinant of topsoil SOC than clay content or iron-bearing minerals, explaining up to 48% of SOC spatial variation. The findings suggest that Al-bearing mineral phases are critical for organic-mineral associations and clay aggregation, with carbon inputs from crop yield improving predictive models of SOC variation.

UK applicability

The findings are potentially applicable to UK arable systems in similar humid temperate climates, particularly where soils are formed from quaternary deposits. However, the study's focus on a single Swedish field site means the results should be validated across diverse UK soil types and management systems before informing national soil carbon management guidance.

Key measures

Oxalate-extractable aluminium (Alox); oxalate-extractable iron (Feox); clay-sized particles (<2 µm); grain yield; total SOC; SOC in different soil fractions (silt- and clay-sized); spatial variation coefficients (R² values)

Outcomes reported

The study quantified relationships between oxalate-extractable aluminium (Alox), clay content, iron-bearing minerals, crop yield and total soil organic carbon (SOC) in arable topsoil. It demonstrated that Alox explained approximately 48% of spatial variation in SOC and that approximately 80% of SOC was stored in silt- and clay-sized fractions.

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