Summary
This meta-analytic appraisal by Chaplot and Smith critically examines 37 field studies on cover crop carbon sequestration globally, finding that all were limited to soil sampling depths of 30 cm or less and lacked proper equivalent soil mass comparisons. After excluding studies with substantial methodological shortcomings, the authors identified only six rigorous trials, of which four showed non-significant trends, one showed negative impacts, and one positive—yielding a mean carbon storage estimate of 0.03 ton ha⁻¹ year⁻¹, roughly 90% lower than prior meta-analytical claims of 0.32 ± 0.08 ton C ha⁻¹ year⁻¹. The authors call for urgent revision of models and policies, alongside improved experimental design and deeper investigation of why cover crops remain inefficient for soil carbon sequestration.
UK applicability
The findings have direct relevance to UK agriculture and climate policy, where cover crops are increasingly promoted as a carbon sequestration tool under schemes such as the Environmental Land Management programme. The substantial downward revision of carbon storage estimates should inform UK policy targets and farm incentive structures, whilst the identified methodological gaps highlight the need for improved long-term field trials under UK soil and climatic conditions.
Key measures
Soil organic carbon stocks (ton C ha⁻¹ year⁻¹), sampling depth, soil mass equivalence, study duration, and methodological quality indicators
Outcomes reported
The study critically reviewed 37 published field trials on cover crop soil organic carbon sequestration, assessing methodological quality and reported carbon storage rates. It found that most existing studies had significant design limitations and reported substantially lower carbon sequestration than previously claimed in meta-analyses.
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