Historical soil amendment with charcoal increases sequestration of non‐charcoal carbon: a comparison among methods of black carbon quantification

Summary

This study examined whether historical (>150 year) charcoal soil amendments enhance carbon sequestration in temperate arable systems, comparing three black carbon quantification techniques. Charcoal-amended 'black spot' soils contained 1.6–1.7 times more maize-derived organic carbon and 1.0–1.4 times more non-charcoal organic carbon than adjacent unamended soil, with differences most pronounced in protected silt and clay fractions. The findings suggest that historical charcoal amendment can promote accumulation of recent plant-derived carbon without displacing older soil organic matter stocks.

UK applicability

These findings are relevant to UK temperate arable systems, particularly those exploring biochar or charcoal-based soil amendments for carbon storage. However, the study examined historical rather than contemporary applications; UK farmers considering charcoal amendment would benefit from long-term field trials under current management practices and climatic conditions.

Key measures

Organic carbon content (%), black carbon quantification via three methods (dichromate oxidation, chemo-thermal oxidation, differential scanning calorimetry), maize-derived carbon via δ13C analysis, carbon distribution in soil fractions (particulate organic matter, silt and clay)

Outcomes reported

The study compared methods for quantifying black carbon in historically charcoal-amended soils and measured the effect on recent and older soil organic carbon sequestration using stable carbon isotope analysis and physicochemical fractionation. Results showed differential accumulation of maize-derived carbon in charcoal-amended versus control soils without depletion of older carbon stocks.

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