Soil carbon usually refers only to the organic matter component of soil, known as soil organic carbon (SOC). However, soil carbon also has an inorganic component, known as soil inorganic carbon (SIC). Solid SIC, often calcium carbonate, tends to accumulate more in dry areas with poor soil, leading many to believe that it is not important.

In a study published in in the journal Science  Researchers led by Prof. Huang Yuanyuan from the Institute of Geographical Sciences and Natural Resources Research of the Chinese Academy of Sciences (CAS) and Prof. Zhang Ganlin from the Institute of Soil Science of the CAS, along with collaborators, have quantified the global trade of SIC, challenging this long-held view.

Scientists have found a whopping 2.305 billion tons of carbon stored as SIC in the top two meters of soil worldwide, more than five times the carbon found in all the world's vegetation combined. This hidden reservoir of soil carbon could be the key to understanding how carbon moves around the world. (Chinese Academy of Sciences, more at phys.org)