Effects of different cropping systems on soil inorganic nitrogen accumulation —A case study in Tongzhou District, Beijing

The effects of different cropping systems on soil inorganic nitrogen accumulation was analyzed using survey and experiments date. The results showed that the ability to recover nitrogen fertilizer under different cropping systems was as the followings: continuous sunflower﹥wheat–corn rotation (field covered with corps) ﹥wheat–corn rotation (without covering)﹥wheat–soybean rotation﹥continuous corn. Reasonable rotation, (i.e. rotation with N2-fixing legumes, rotation with deep-rooted crops) and stubble–mulch, were recommended because they could utilize NO3--N from the subsoil, prevent losses of nutrients from leaching. The amount of NO3--N accumulation and NH4+-N accumulation in vegetable field in 0–2 m soil layer was 1935.03 kg/ha and 201.8 kg/ha respectively. The high concentration of residue NO3--N indicated that the rate of N input should be reduced, and cropping sequence should be adopted to enhance the utilization efficiency of NO3--N from the soil at depths blow the rooting zone.