Inorganic Carbon Should Be Considered for Carbon Sequestration in Agricultural Soils

Improved agricultural practices that restore soil organic carbon (SOC) are recognized as climate solutions, whereas soil inorganic carbon (SIC) is ignored nearly in all practices. Here, we meta-analyzed the joint response of SOC and SIC to six common agricultural practices, i.e., reduced tillage, irrigation, fertilization, residue utilization, reclamation, and restoration. The results demonstrated that the most agricultural practices strongly increased SOC, whereas SIC was less sensitive. SOC and SIC increased synergistically by following practices: Irrigation, biochar application, and improved reclamation. However, "trade-offs" between SOC and SIC due to mineral fertilizer application and restoration to forestland may partly offset soil carbon sequestration. The magnitude of SOC changes decreased with increasing depth, and deep SOC was still responsive to agricultural practices. In contrast, SIC loss occurred mainly in the topsoil, while increases were mainly in the deep soil. By optimizing agricultural practices, we estimated the global potential of carbon sequestration in soil at 1.5 Gt yr.^-1 (95% confidence interval: 0.3-2.8), with SOC contributing 1.4 Gt yr.^-1, while SIC contributed less (0.1 Gt yr.^-1) due to its losses under some practices. This potential is equivalent to 16% of global fossil fuel emissions. Concluding, this study highlights the potential contribution of SIC in enhancing the integrity of soil-based climate solutions, broadening the scope of carbon management in mitigating climate change.