Soil organic carbon in cropland across different terrains on the Qinghai-Tibet Plateau

Northwest alpinecold region is an important part of China's agricultural production. Understanding soil organic carbon (SOC) storage and its influencing factors in northwest alpinecold region contributes to accurately evaluate change of national soil organic carbon storage, and also may provide early warning information on response of SOC to climate and management measures in croplands with same latitude or lowaltitude. Based on two landform types (slope and bottom) and three soil types (chernozem, kastanozem and sierozem), soil samples from seventyfive sites were collected for investigating distribution characteristics of cropland SOC contents and the relationship with terrains in Ledu county of Qinghai province. The cropland surface (0 -20 cm) SOC contents range from 4.38 g/kg to 20.81 g/kg with the average of 11.29 g/kg in Ledu county, and the SOC contents in the three soil types follow the decreasing order as: chernozem＞kastanozem＞sierozem. There are no significant differences of surface SOC contents (0-20 cm) in different terrains, however, there are significant differences in the subsoil SOC contents (20-100 cm). Compared with the three soil types in bottom, the subsoil SOC contents of the same soil type in the slope are increased by 111.5%、 62.5% and 66.3%. The SOC contents in the vertical layers have differences in different terrains. The surface SOC contents (0-20 cm) are higher than those of the subsoil (20-100 cm) in the bottom in the same soil type, and the SOC contents in the subsoil (20-100 cm) are higher than those of the surface soil in the slope in the same soil type. Compared with the subsoil (20-100 cm) SOC contents of the three soil types in the bottom, the surface (0-20 cm) SOC contents are increased by 18.7%, 24.3% and 153.5%. Compared with the surface (0-20 cm) SOC contents of the three soil types in the slope, the subsoil (20-100 cm) SOC contents are increased by 46.9%, 8.0% and 1.0%. These results are contribution to the study of accurately estimating the cropland SOC in the Qinghai Tibet Plateau.