High organic carbon content constricts the potential for stable organic carbon accrual in mineral agricultural soils in Finland

Summary

This analysis of agronomic soil test data covering approximately 95% of Finland's farmed land reveals that most mineral agricultural soils currently hold organic carbon stocks exceeding their mineral matter's capacity for stable protection. Whilst 32–40% of soils retain potential for further mineral-associated organic carbon accumulation, particularly in southern high-clay areas, the nationwide climate mitigation potential of additional sequestration in the top 15 cm is modest at less than 2% of annual greenhouse gas emissions. The findings suggest that maintaining existing high organic carbon stocks through farming practices that maximise carbon input is a more critical priority than expanding sequestration, particularly in high-organic-carbon soils facing carbon loss risks under climate change.

UK applicability

The UK's more temperate maritime climate and different soil mineralogy compared to Finland may yield different saturation dynamics for organic carbon protection; however, the methodological approach of assessing mineral-matter-limited sequestration potential is directly transferable. UK arable soils, particularly those with lower clay contents, may show higher sequestration potential than Finland's mineral soils, but the underlying principle—that preservation of existing stocks often outweighs net sequestration gains—is likely broadly applicable to UK farming policy.

Key measures

Organic carbon (OC) content, mineral-associated organic carbon (MOC) capacity, clay and fines (clay + silt) content, clay/OC and fines/OC ratios, soil organic carbon stock (0–15 cm depth), potential for additional organic carbon sequestration (Tg annually)

Outcomes reported

The study estimated the organic carbon sequestration potential of the top 15 cm of mineral agricultural soils across Finland, finding that 32–40% of soils have capacity for further mineral-associated organic carbon accumulation, whilst the majority exceed their mineral matter's protective capacity. The nationwide sequestration potential was quantified at 0.21–0.26 Tg annually, representing less than 2% of Finland's annual greenhouse gas emissions.

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