Abstract: A study was conducted to analyze the distribution of soil organic carbon of terraced fields and the effects of topographic factors and human activities in Aohan, Chifeng, Inner Mongolia. The results showed that the soil organic carbon content was the range of 0.87-10.25 g·kg^-1 within 1 m depth of terraced area and averaged at 5.91 g·kg^-1. There were significant differences in soil organic carbon content among different layers; the organic carbon content decreased with increasing the soil depth. The average content of soil organic carbon was 7.54 g·kg^-1 in surface layer (0-20 cm), being 1.32 times and 1.67 times of that in the middle (20-60 cm) and bottom (60-100 cm) layers, respectively. The effects of slope position on soil organic carbon were in order of upper slope < middle slope < lower slope, and the effects of slope direction were in order of shady slope > semi-shady slope > semi-sunny slope > sunny slope.  Effects of human activities on soil organic carbon content of terraced fields were mainly embodied in the different cultivation and management measures; straw returning and no-till methods helped improve soil organic carbon content.

Key words: mixed crop-livestock system, nitrogen flow characteristic, nitrogen use efficiency, North China Plain, farm level