The six‑year field experiment reported in [1] directly compares the long‑term carbon sequestration potential of mineral fertilizer, compost, and a walnut‑shell biochar amendment. Results show that biochar markedly enhances stable carbon storage relative to mineral fertilizer, with biochar‑treated plots retaining higher amounts of recalcitrant carbon and exhibiting slower mineralization rates. The study attributes this to biochar’s aromatic, condensed structure, which resists microbial decomposition, and its capacity to improve soil aggregation, thereby physically protecting organic matter from mineralization.

In contrast, mineral fertilizer supplies readily available inorganic nutrients but contributes little to persistent soil carbon; any associated organic carbon is quickly mineralized, leading to modest or transient increases in soil carbon pools. Compost, while providing more labile organic carbon than mineral fertilizer, still undergoes relatively rapid mineralization compared with biochar, though it does improve microbial biomass and short‑term carbon turnover.

Overall, for long‑term carbon storage, biochar outperforms both mineral fertilizer and compost by reducing mineralization rates and promoting the formation of stable carbon fractions. The findings suggest that incorporating biochar into agricultural soils is a more effective strategy for durable carbon sequestration than relying on mineral nutrient inputs alone.