Effects of soil aggregate stability on soil N following land use changes under erodible environment

Soil nitrogen (N) dynamics have considerable effects on the terrestrial carbon cycle, and land use changes could affect soil N through impacts on soil aggregate stability. This study selected nine sites including apple orchards of different ages and restored sites to explore the effects of soil aggregate stability on soil total N (STN), ammonium N (AN), and nitrate N (NN) following different stages of apple orchard on the Loess Plateau of China. The results showed that when compared with apple orchard sites, the restored sites had higher contents of STN and lower contents of AN and NN, but when compared with restored sites, inorganic-N storage played a more important role in the apple orchards. Following different stages of apple orchards, the STN, AN and NN contents and mean weight diameter (MWD) of soil aggregates were all improved. MWD had a negative effect on inorganic-N content at 10-30 cm soil depths but had a positive relationship with soil N at 0-10 cm soil depth. In addition, planting apple orchards destroyed soil aggregate stability in this erodible environment, but it could be restored soon after abandonment. Therefore, considering soil N and soil aggregate stability, it is feasible to plant apple trees in this area and we propose that the effects of trade-offs between soil aggregate stability and soil erosion on soil N in terraced agroecosystems should be a focus of future research.