Storages of soil organic carbon and nitrogen and land use changes in China: 1990-2000

The impacts of land use changes on soil organic carbon (SOC) and soil organic nitrogen (SON) storage have been analyzed from 1990 to 2000 in China between forest, grassland and cropland based on 2473 soil profiles and Landsat TM images from the end of 1980s to the end of 1990s. Estimation of the greenhouse gasses inventory approach suggested by IPCC indicated that the losses of SOC and SON pools were 77.6±35.2 TgC (Tg = 10⁶ t) and 5.6±2.6 TgN to a depth of 30 cm in China, in which the mean annul losses of SOC and SON were 7.76 TgC/yr and 0.56 TgN/yr, respectively. SOC and SON pools of cropland increased 79.0±7.7 TgC and 9.0±0.7 TgN, grassland lost 100.7± 25.9 TgC and 9.8±2.2 TgN, and forest lost 55.9±17.0 TgC and 4.9±1.1 TgN, respectively. In order to estimate the uncertainty range of calculated results, this paper adopted the land use conversion approach to compare with IPCC's approach. The calculation of the land use conversion approach showed that the losses of SOC and SON pools were 53.7 TgC and 5.1 TgN to a depth of 30 cm, and 99.5 TgC and 9.4 TgN to a depth of 100 cm respectively, which the calculation procedure was designed according to the conversion area and the changing rate of SOC and SON densities among forest, cropland and grassland during 10 years.