The importance of biochar quality and pyrolysis yield for soil carbon sequestration in practice

Summary

This meta-analysis evaluated biochar's carbon sequestration potential by synthesising published data meeting international quality standards. The authors demonstrate that carbon sequestration efficiency from stable biochar ranges from 25–50% of feedstock carbon and varies non-linearly with the hydrogen-to-organic carbon ratio, a key quality criterion in emerging EU regulations. The analysis suggests that pyrolysis at 500–550°C, producing biochar with H/Corg of 0.38–0.44, optimises soil carbon sequestration efficiency at approximately 41% over a 100-year timeframe.

UK applicability

These findings are directly applicable to UK policy and practice, as the EU Biochar Certificate and International Biochar Initiative standards referenced are used for quality assurance in UK biochar markets. The optimal pyrolysis temperature and H/Corg ranges identified could inform UK agricultural guidance on biochar selection for climate mitigation projects.

Key measures

Carbon sequestration efficiency (% of feedstock carbon); fraction of biochar carbon remaining after 100 years (Fperm); hydrogen-to-organic carbon ratio (H/Corg); pyrolysis yield; pyrolysis temperature

Outcomes reported

The study evaluated biochar carbon sequestration efficiency by calculating the fraction of biochar carbon remaining in soil after 100 years as a function of feedstock type and pyrolysis temperature, expressed via the hydrogen-to-organic carbon ratio. It identified optimal pyrolysis conditions for maximising carbon sequestration from plant-based feedstocks.

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