Agronomic impacts on soil inorganic carbon: A meta-analysis of the mediating roles of soil properties and climate factors.

Soil inorganic carbon (SIC) constitutes a substantial proportion of the global soil carbon pool and plays a critical role in long-term carbon sequestration, and its sequestration is influenced by agronomic practices and climatic factors. However, the interactive effects between agronomic practices, climatic factors, and SIC remain poorly understood. Hence, a global meta-analysis was conducted to quantify the effects of different agronomic activities on SIC content, elucidate their underlying mechanisms, and evaluate the mediating roles of soil properties and climatic factors in shaping these responses. The study showed that straw return, biochar, and mineral additions increased SIC content by 20.79%, 12.48%, and 72.15%, respectively, whereas no-tillage and fertilization reduced it by 10.34% and 7.53%, respectively, compared with the control. However, the 72.15% increase under mineral addition stems mainly from the direct input of carbonate-containing rock powders rather than net removal of atmospheric CO2. This distinction must be considered when evaluating the climate mitigation potential of this practice. Straw return and biochar addition accelerated carbon mineralization by increasing soil pH and enhancing soil microbial activity; mineral addition directly introduced carbonates into the soil. This had the most significant effect on increasing SIC content. In semi-humid and humid regions, no-tillage reduced mineralization efficiency by reducing topsoil disturbance and restricting microbial activity. Fertilization led to soil acidification, which was unfavorable for the formation of inorganic soil carbon. In addition, SIC content was positively correlated with soil pH and depth and negatively correlated with mean annual temperature and mean annual precipitation. This study suggests that in arid and semi-arid regions, practices such as straw incorporation, biochar application, and mineral amendments can effectively enhance SIC sequestration by promoting carbonate formation and stabilization.