Abstract:The soluble nitrogen component of soil is the most active part of the nitrogen cycle, and it is the key link between "plants-soil nitrogen components-soil nutrients". Therefore, in order to explore the effects of vegetation types on the accumulation and availability of soil nitrogen in the loess hilly and gully region, this paper took four typical vegetations (barren grassland, Hippophae rhamnoides, Xanthoceras sorbifolium, Picea asperata) as the research objects. We analyzed the difference of soluble organic nitrogen (SON), ammonium nitrogen (NH4+—N), nitrate nitrogen (NO3-—N) contents, density and the proportion of TN in the 0—10, 10—20, 20—40 cm soil layers. The results showed that compared with the barren grassland, the SON content in the 0—40 cm soil layer showed the highest performance in Picea asperata (19.0%), and the SON contents under Xanthoceras sorbifolium and Hippophae rhamnoides were decreased by 7.0% and 13.2% respectively. The NO3-—N content was the highest under Hippophae rhamnoides (20.9%), and the contents under Xanthoceras sorbifolium and Picea asperata were decreased by 5.0% and 48.0% respectively. Compared with barren grassland, the NH4+—N contents under three vegetations were decreased by 19.0%~29.1%. Similarly, the SON density of Picea asperata was increased by 31.17%, and the values under Hippophae rhamnoides and Xanthoceras sorbifolium were decreased by 12.8% and 4.3% respectively. The NO3-—N density of Hippophae rhamnoides was increased by 21.4%, and the NO3-—N densities under Xanthoceras sorbifolium and Picea asperata were decreased by 3.5% and 42.6% respectively. The NH4+—N densities of the other vegetations were decreased by 16.4%~32.8%. In addition, among the proportion of soluble nitrogen in TN, only Hippophae rhamnoides NO3—N accounted for the highest proportion of TN, which was 1.2 times higher than that of wasteland. Correlation analysis showed that the soluble nitrogen component was more affected by TN and MBN than SOC and MBC. In summary, different vegetations had great impact on the soluble nitrogen content, density and the proportion of total nitrogen. Among them, Picea asperata and Hippophae rhamnoides had the better effect on increasing nitrogen availability.