In the world, over 2,300 billion tons of carbon are stored in the first two meters of soil in the form of inorganic substances, in practice a quantity five times higher than that present in all the world's vegetation combined. This enormous 'reserve' of carbon that has so far been ignored, but is fundamental in the fight against climate change, has been identified by a study published in Science by researchers from the Chinese Academy of Sciences.
Usually when we talk about the carbon stored in the soil we refer to the one fixed in the organic matter, the so-called 'Soc' (soil organic carbon), but in reality there is also another important inorganic component called 'Sic' (soil inorganic carbon) which is not considered. Solid Sic tends to accumulate usually as calcium carbonate in unproductive soils in arid regions, which led many to believe that it wasn't that important. Chinese researchers led by Huang Yuanyuan have calculated that globally there are 2,305 billion tonnes of carbon stored as Sic in the top two meters of soil, a hidden reserve that could be key to better understanding the carbon cycle on Earth.
“The bottom line is that this huge carbon pool is vulnerable to environmental changes, particularly soil acidification,” Huang explains. "Acids dissolve calcium carbonate and remove it as carbon dioxide or directly into the water. Many regions in countries such as China and India are affected by soil acidification due to industrial activities and intensive agriculture. Without action corrective measures and best practices for soil, the world is likely to face alterations of Sic in the next thirty years", with a major impact on ecosystems. Researchers estimate that approximately 1.13 billion tons of inorganic carbon is lost from soils into inland waters each year. This loss has profound but often overlooked implications for carbon exchange between soil, atmosphere, freshwater and ocean.