CHANGES IN ORGANIC CARBON OF CULTIVATED SOILS IN CHINA FROM 1980 TO 2000

Based on measured data of soil organic carbon from 75 plots and 205 regions in China,changes in organic carbon density from 1980 to 2000 in cultivated soils in China, causes of the changes and future trends were addressed. The results show that the average organic carbon density in cultivated soils has experienced a carbon gain during the period. The significant carbon gains are in fluvo-aquic soils in North China,brown earths in lower reaches of the Liaohe River and paddy soils in South China, and the increases are 19%(0.24 kg/m²),14%(0.29 kg/m²) and 16%(0.29 kg/m²) respectively.On the contrary, SOC have decreased by 27%(1.01 kg/m²) in the Latosols in Southwest China and by 3%(0.11 kg/m²) in Phaeozems and Chernozems in Northeast China. There are no changes in dark loessial soils and loessial soils in the Loess Plateau, Cinnamon soils in Shanxi Province and irrigated silting soils in northeastern Xinjiang. The distribution of soil organic carbon density is consistent with the climatic zone from 1980 to 2000, but a significant negative relationship between the carbon change and its original content in early 1980s was revealed, and 4~5 kg/m² is the critical value for increasing and decreasing. The SOC increase in lower soil carbon content regions is mainly driven by improved human management practice such as the expansion of irrigation and fertilization in recent years, while the decrease in higher content regions could be due to the short-time intensified tillage and its high original content. In the coming 30~50 years the cultivated soil would increase by 51%,26%,7%,17%,and 30% respectively in North, Northwest, Southeast, Southwest and Northeast China by improving land management, based on comparing with their noncultivated counterpart and assuming a restoration of~50% of the lost SOC. It would provide a considerable potential to sequestrate carbon from the atmosphere in China.