Spatial variability of soil mineral nitrogen in a small catchment in the wind-water erosion crisscross zone of Loess Plateau

Objective of this study was to understand the spatial pattern of soil nutrient properties and their relationships with environmental factors in a small catchment. Spatial pattern and variability of surface (0-10, 10-20, 20-40 cm) soil ammonium and nitrate in a small catchment were analyzed combining with classical statistical and geo-statistics with data measured by non-uniform sampling method in the wind-water erosion of the Loess Plateau. Results showed that mixed land uses patterns developed by the spatial arrangement of different land uses could trap the runoff and sediments, which ultimately formed the plaque mosaic patterns of soil mineral nitrogen on the slope. Soil ammonium and nitrate presented moderate variability, and had moderate spatial autocorrelation. The spatial variability could be controlled by intrinsic variations in soil characteristics (texture, mineralogy, soil genesis processes and terrain) and extrinsic variations (soil fertilization and cultivation practices). The study built the spatial multiple regression-prediction models of soil mineral nitrogen under different soil layers. There were different variables entered to these models, which meant that at different soil depths, there were different environmental factors controlled the spatial variability of soil ammonium and nitrate. The results suggested that creating a mosaic pattern by land use arrangement and more nutrient matter input would improve the soil quality effectively on the hilly area of the Plateau.