Distribution of soil inorganic carbon storage and its changes due to agricultural land use activity in China

The accurate estimation of soil carbon (C) stocks is a necessary component for understanding the global C budget. Although the importance of soil organic C (SOC) within the C cycle is well established, the quantity of soil inorganic C (SIC, including lithogenic and pedogenic inorganic C) pool, another important soil C pool component, has been poorly studied to date. In this study, soil profile data compiled by China's second national soil survey conducted in the 1980s was used to investigate the spatial distribution of SIC for the entire country under present day conditions as well as changes in SIC under historical land use. Results showed that the total SIC storage in China was approximately 55.3 ± 10.7 Pg C with a current average content of 6.3 ± 1.2 kg C m−2, representing 5.8% of the global SIC pool. Land use has significantly affected SIC levels in cultivated soils. Approximately 51% of total cultivated soil surfaces in China have experienced C loss where the most significant loss has been observed in the eastern part of northern China in dry farmlands as well as irrigated soils and paddy soils. On the contrary, SIC has increased (∼10%) in irrigated soils in northwestern China. No significant change (∼39%) has been observed in soils in southern and the eastern part of northeast China. The total loss of SIC in China was approximately 1.6 Pg C due to extensive human activity. Results of this study indicate that human activity may have had a great impact on SIC as well as SOC pools.