Quantitative estimation on carbon sequestration potential of agricultural by-products biochar using chemical oxidation

To accurately evaluate biochar’s carbon sequestration potential, it is essential to quantify the unstable carbon in biochar that soil microbes can mineralize. Chemical oxidation has been used in most studies as a rapid method to estimate the unstable carbon in biochar. However, it remains unclear whether the unstable carbon fraction obtained by chemical oxidation corresponds to the mineralized carbon in soil. This study aimed to establish a chemical oxidation method that matches the chemically oxidized carbon to the fraction mineralized in soil, thereby enabling an accurate assessment of the carbon sequestration potential of biochar. By comparing oxidants and doses, the chemical oxidation method was optimized, and a condition of 30 mmol K₂Cr₂O₇/30 mmol H₂SO₄/g biochar was proposed. This condition showed a strong correlation with mineralized carbon (R² = 0.87, p = 0.01). Based on the proposed chemical oxidation method, hanwoo manure and swine manure-derived biochar exhibited the highest carbon sequestration potential. These findings suggest that chemical oxidation is an effective strategy for assessing biochar carbon stability without long-term incubation.