Land use effects on the dynamics of soil carbon, nitrogen and microbes in the water-wind erosion crisscross region of the northern Loess Plateau

The water-wind erosion crisscross region of the northern Loess Plateau is under constant pressure from severe erosion due to its windy and dry climate and intensive human activities. Identifying sustainable land use patterns is key to maintaining ecosystem sustainability in the area. Our aim is to appraise the impacts of different land use regimes on the dynamics of soil organic C, total N and microbes in a typical watershed in the northern Loess Plateau to identify suitable land use types that sustain soil fertility and sustainability. A field experiment was performed in Liudaogou, where the dynamics of soil organic C and total N, microbial biomass carbon and nitrogen, microbial respiration and net N mineralization in six typical land use types, dam land, rainfed slope land, broadleaf deciduous forestland, conifer evergreen forestland, shrubland and grassland, were measured in three different growing seasons. Land use type and season significantly affected the soil organic C, total N, and dynamics of microbial biomass and activities. As the most anthropogenically disturbed land use pattern, dam land is an optimal land use pattern for organic C sequestration due to its higher soil organic C (13.13 ± 0.31 g kg-1) and total N (0.76 ± 0.03 g kg-1) but lower soil microbial activity (28.90 ± 2.48 mg CO2 kg-1 d-1). Soil organic C, total N and microbial properties demonstrated a decreasing trend after the natural grassland was converted to shrubland, forestland and rainfed slope land. Shrubland with exotic N-fixing Korshinsk peashrub (Caragana korshinskii Kom) can maintain soil organic C, total N and microbial properties similar to grassland. Soil total organic C, ammonium nitrogen, total N, soil moisture and extractable C were the principal indexes for the soil microbial biomass and activity and explained 88.90% of the total variance. Consequently, grassland is the optimal land use pattern in the water-wind erosion crisscross region of the northern Loess Plateau to maintain ecosystem stability and sustainability.