Soil organic carbon change in UK mineral and organo-mineral soils since 2000: a systematic evidence map and critical narrative synthesis

Licida M Giuliani, Laura Bentley, Ryan McGuire, Paul N Williams, Bridget Emmett, Ellen Fay, Tilly Kimble-Wilde, Pete Smith

Soil organic carbon is increasingly embedded in United Kingdom climate and land-use policy, yet the empirical basis for estimating its long-term change in mineral and organo-mineral soils remains uncertain. We conducted a systematic evidence map and critical narrative synthesis of peer-reviewed and grey literature published between 2000 and 2025 to evaluate soil organic carbon stocks and changes associated with land-use transitions and management practices. Seventy-five studies met predefined eligibility criteria. Evidence was unevenly distributed across land uses, depths and study designs, with most measurements restricted to topsoil layers and few long-term, full-profile assessments. Reporting of contextual variables, including soil type, soil properties and management history, was often limited or inconsistent, restricting assessment of how SOC responses vary across environmental settings. Frequently studied cropland-to-grassland and cropland-to-woodland transitions showed predominantly positive SOC stock outcomes, whereas management responses were generally mixed. Only two of 75 studies provided empirical evidence relevant to reversibility, while evidence on the development and persistence of stable SOC states was very limited. Heterogeneity in metrics, depth coverage, study duration and contextual reporting limited comparability and precluded quantitative meta-analysis. As a result, inconsistent signals across the recent UK literature appear to reflect limitations in study design, reporting and evidence availability more than clear evidence that land-use or management interventions lack sequestration potential. The post-2000 UK evidence base has strengthened confidence in qualitative conclusions, particularly for major land-use transitions, but has not substantially reduced uncertainty regarding the magnitude, persistence, reversibility or whole-profile extent of soil organic carbon change. The evidence map supports qualitative interpretation of recurring patterns, including plausible SOC gains under certain land-use changes and management practices, but does not provide robust UK-specific sequestration rates. Soil organic carbon sequestration should therefore be treated as a context-dependent and bounded mitigation option that may deliver important soil-health and ecosystem co-benefits alongside potential climate benefits.