Biogeochemistry characteristics of nitrogen in unsaturated soils of Jinghuiqu irrigation district

Biogeochemistry characteristics of an unsaturated zone in Jinghuiqu irrigation district of China was studied to analyze the predominant interacting factors of nitrogen concentration and transformation in the vadose zone under long term flood irrigation using river water and groundwater sources alternatively. The site was instrumented for soil sampling at various depths above the groundwater table at 4 meters below the soil surface. The measured concentrations of the biogeochemicals (TN, N-NO₃^-, N-NH₄⁺, and several microorganisms) showed that there exist “active” and “inactive” layers in the profile, which were distinguished by the combined amount of clay and silt particles in the soil. Most parameter values increase sharply in the “active” layers and decrease sharply in the “inactive” layers. In the active zone, the N-NO₃^- was concentrated and more transformed by microorganisms. All the N concentrations, in NNO₃^-, N-NH₄⁺ and TN, were mainly affected by the amounts of organic matter and microorganisms.