New Insights into the Enhancement Effect of Exogenous Calcium on Biochar Stability during Its Aging in Farmland Soil

Converting biowaste into biochar and incorporating it soil is recognized as an effective method for carbon (C) sequestration. However, inevitably undergoes aging process in soil, which influences its stability, ultimately threatens sequestration ability. This study selected CaCl2 exogenous additive of sewage sludge bone dreg producing Ca-rich biochars, both surface C bulk stability them were investigated under three processes (dry–wet aging, freeze–thaw natural farmland soil). The results showed that the above resulted oxidized decreasing by 10~23%, 28~41%, 0~74%, respectively, compared with pristine biochar, while decreased 6~10%, 0~1%, 0~35%, respectively. was attributed to “protective effect” Ca-containing crystals on surface, including CaO, Ca5(PO4)3Cl, Ca5(PO4)3(OH), Ca8H2(PO4)6·H2O, Ca10(PO4)6(OH)2, intervened oxidation C–C/C=C but also reduced generation a fragmented structure. By comprehensively assessing processes, final increased 27~80%, (23~74%). Therefore, more dominant than considering potential during long-term soil.