Based on the field investigation, combined with collecting soil sample and laboratory analysis, the characteristics of soil organic nitrogen fractions (Bremner) in the different degree desertification grassland (non-desertification, light-desertification, moderate-desertification, heavy-desertification and severe-desertification) of the different soil layers (0-20, 20-40, 40-60, 60-80 and 80-100 cm) in the Northwest of Sichuan were studied. Results show that: during the process of grassland desertification, different layers of soil organic nitrogen group content showed a downward trend, which 0-20 cm soil layer was most obvious, THAN, NAHN, AN, AAN, ASN and HUN were reduced 90.58%, 69.28%, 91.44%, 91.01%, 87.77% and 88.99%; Compared with the non-desertification grassland, the content of the soil organic nitrogen fractions of the severe-desertification grassland showed the different decrease amplitude: AAN> AN> HUN> ASN> NAHN; compared with HUN, ASN and NAHN, the organic nitrogen components changed in AN and AAN were relatively large, and more sensitive to the ecological environment; there were significant differences in the contents of organic nitrogen components in different desertification stages, but the decline of the early stage of grassland desertification was relatively large, and the decrease in the late period of the desertification was relatively small, showed that the loss of the soil organic nitrogen element was more severe during the early stage of grassland desertification. Thus improving the grassland desertification in time is significant for preventing nitrogen loss in soil desertification.
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