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 years) charcoal amendments to soil continue to enhance carbon sequestration in a temperate maize-growing system. Using isotopic tracing and three independent black carbon quantification methods, the authors found that charcoal-amended soils ('black spots') contained significantly more recent maize-derived carbon and non-charcoal organic carbon than adjacent unamended soils, with carbon preferentially accumulating in physically protected silt and clay fractions. The findings demonstrate that historical charcoal amendment increases carbon accumulation without displacing pre-existing soil organic matter, though black carbon content estimates varied substantially by detection method.

UK applicability

These findings are potentially relevant to UK arable systems and soil carbon management practices, though the study was conducted in a temperate climate context (likely continental Europe based on journal and author affiliations). The results support investigation of biochar or charcoal amendment as a soil carbon sequestration strategy in UK cereal production, though localised trials would be needed to validate applicability under UK soil and climatic conditions.

Key measures

Organic carbon percentage; black carbon content by three quantification techniques (Cr₂O₇, CTO-285, DSC); δ¹³C isotopic analysis; maize-derived (C₄) and pre-existing (C₃) carbon pools; physicochemical fractionation (particulate organic matter, silt and clay fractions)

Outcomes reported

The study compared three black carbon quantification methods (dichromate oxidation, chemo-thermal oxidation, differential scanning calorimetry) to assess effects of historical charcoal amendments on recent and older soil organic carbon sequestration in maize-cropped topsoils. It measured organic carbon content, black carbon content, and physically fractionated carbon stocks in soils with versus without historical charcoal application.

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