Abstract: This study investigated the changes of soil organic carbon and nitrogen in a desert steppe ecosystem in Ningxia under grazing (CK) and different vegetation restoration regimes, which included deep ploughed (S), shallow ploughed (Q), no-tillage (M) and enclosed (F). Soil samples were collected from 0-10 cm, 10-20 cm, 20-30 cm, and 30-40 cm soil depths. The results showed that the soil organic carbon contents were significantly greater (P<0.05) in the shallow ploughed treatment (14.90 and 14.50 g·kg^-1 in the 0-10 cm and 10-20 cm soil layers, respectively) than those in deep ploughed, enclosed and grazing treatments. For the 20-30 cm soil layer, the organic carbon content in the different treatments ranged from 5.03 to 9.93 g·kg^-1, and was highest in the shallow tillage treatment and lowest in the enclosed treatment (P<0.05). The total nitrogen (TN) contents for the 0-10 cm and 10-20 cm soil layers were both highest in the shallow ploughed treatment (0.17 and 0.22 g·kg^-1, respectively), and they were significantly higher (P<0.05) than those in the enclosed and grazing treatments. For the deeper soil layers, the total nitrogen contents were highest in the deep ploughed treatment (0.14 and 0.13 g·kg^-1, respectively, for 20-30 cm and 30-40 cm soil depths), while those in the enclosed treatment were significantly lower (P<0.05). Expressed on an area basis, the soil organic carbon densities in different soil layers of the various treatments ranged between 0.49 and 1.58 kg·m^-2, while the total nitrogen densities ranged from 0.013 to 0.039 kg·m^-2. The soil organic carbon densities at each depth of 0-40 cm layer and the total nitrogen densities at 0-10 cm and 10-20 cm were higher in the shallow ploughed and lower in the enclosed treatment. The total nitrogen densities for the 20-40 cm soil depth were highest in the deep ploughed and lowest in the enclosed treatment. For the 0-40 cm soil depth, the soil organic carbon and total nitrogen reserves in the shallow ploughed treatment were 47.72 and 1.09 t·ha^-1, respectively, and were significantly higher than those in the enclosed treatment (P<0.05). Thus, the shallow ploughed treatment is the most conducive among the tested treatments for accumulation of soil organic carbon and nitrogen reserves in desert steppe grassland of this region.

Key words: desert steppe, restoration measure, soil organic carbon, total nitrogen