Soil inorganic carbon, the other and equally important soil carbon pool: distribution, controlling factors, and the impact of climate change

Soil inorganic carbon (SIC) contributes to up to half of the terrestrial C stock and is especially significant in arid and semi-arid environments, yet has not been explored as much as soil organic carbon (SOC). SIC plays an important role in agriculture, CO2 sequestration and emission and climate regulation. To address this, a comprehensive review is presented on the digital mapping of soil inorganic carbon including a discussion of SIC vertical variation, its controlling factors, and sequestration/emission capability. We surveyed SIC distribution and mapping efforts in Australia, South Africa, Chile, the Mediterranean basin, Iran, China, France, and the United States. We found that current detailed spatial information on SIC distribution and stock is relatively scarce and digital soil mapping (DSM) efforts to address this are modest. Furthermore, we do not have a complete soil C model that explicitly accounts for all sources and sinks of soil carbon. This review showed that many aspects of SIC in DSM and soil C studies have been so far ignored and that SIC has a crucial role in climate regulation. This review provides some insights into the importance and unknown aspects of SIC.