Abstract: This paper studied the distribution patterns of organic carbon (OC), total nitrogen (TN), NH₄⁺-N, and NO₃^--N in the profiles of brown calcic soil, grey cinnamon soil, chestnut soil, and alpine meadow soil in the middle of Qilian Mountains. In all test soils, the contents of OC, TN, NH₄⁺-N, and NO₃^--N decreased with increasing soil depth, and the accumulation and decomposition of OC and various N forms differed with soil types. The average content of OC in different soil profiles changed from 14.01 to 41.17 g·kg^-1, and was in the order of grey cinnamon soil > alpine meadow soil > chestnut soil > brown calcic soil; the average content of TN changed from 1.28 to 2.73 g·kg^-1, with a sequence of alpine meadow soil > grey cinnamon soil > chestnut soil > brown calcic soil. The C/N ratio was from 11.33 to 19.22, with the order of grey cinnamon soil > chestnut soil > alpine meadow soil > brown calcic soil. NH₄⁺-N content changed from 5.80 to 8.40 mg·kg^-1, and was in the order of brown calcic soil > alpine meadow soil > chestnut soil > grey cinnamon soil; NO₃^--N content changed from 6.57 to 15.11 mg·kg^-1, being in the order of chestnut soil > alpine meadow soil > brown calcic soil > grey cinnamon soil. The ratio of NO₃^--N to NH₄⁺-N was 1.00-2.69, with the sequence of grey cinnamon soil > chestnut soil > alpine meadow soil > brown calcic soil. The OC and N contents in the same soil types differed significantly with the conditions of climate, vegetation, and topography (e.g., slope aspect and slope position). Correlation analysis showed that there were highly significant positive correlations between OC, TN, and NH₄⁺-N, but these three items had no significant positive correlations with NO₃^--N. Furthermore, there were highly significant positive correlations between available K, NH₄⁺-N, and NO₃^--N and between available P and OC, significant positive correlations between available P, TN, and NH₄⁺-N, but no significant correlations between pH, total K, and total P and OC and N.

Key words: Qilian Mountains, soil profile, organic carbon, nitrogen