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

Summary

This field study examined whether historical charcoal amendments to temperate agricultural soils enhance carbon sequestration in maize cropping systems. Soils from former charcoal production sites contained 1.6–1.7 times more recent maize-derived organic carbon and 1.0–1.4 times more non-charcoal organic carbon than adjacent unamended soils, with additional carbon concentrated in physically protected silt and clay fractions. The findings suggest that long-term charcoal amendment promotes accumulation of recent organic carbon without depleting older soil carbon stocks, though the magnitude of effect varies by black carbon quantification method.

UK applicability

These findings are relevant to UK arable farming, particularly under temperate climates comparable to the study conditions. Charcoal soil amendments could potentially enhance carbon sequestration in cereal cropping systems, though site-specific factors and current UK soil carbon baseline conditions would require consideration before wider adoption.

Key measures

Percentage of soil organic carbon (OC); black carbon (BC) content quantified by three methods (dichromate oxidation, chemo-thermal oxidation CTO-285, differential scanning calorimetry DSC); δ13C isotopic analysis; maize-derived carbon content; soil physicochemical fractionation (particulate organic matter, silt and clay fractions)

Outcomes reported

The study compared soil organic carbon (SOC) sequestration in maize-cropped soils with historical (>150 years) charcoal amendments versus adjacent unamended soils, using multiple black carbon quantification methods and stable isotope analysis. It measured both recent maize-derived and older soil organic carbon pools to assess whether historical charcoal application enhanced carbon accumulation without depleting existing stocks.

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