The Characteristic And Parametric Estimation Of Soil Nitrogen Mineralization, Nitrification And Denitrification Kinetic For Various Land Uses In Subtropical Central China

Soil nitrogen mineralization, nitrification and denitrification are important processes in nitrogen cycle. Soil nitrogen mineralization is crucial to understand soil potential nitrogen. Greenhouse gases (N2O) are produced by soil nitrification and denitrification, which are the major ways of soil nitrogen loss in ecosystem. Soil physical and chemical properties, along with land uses, will affect soil mineralization, nitrification and denitrification process. Therefore, the comparative analysis of soil nitrogen mineralization, nitrification and denitrification for different land uses, and effect factors, as well as predictive models, are helpful to know soil nitrogen transformation efficiency and predict soil greenhouse gas emissions.In this study, five kinds of different land uses (vegetable soil, paddy soil, forest soil, wasteland soil and tea garden soil) were selected and sampled in Jinjing town, Hunan Province. We analysized the difference between soil nitrogen mineralization, nitrification and denitrification and the influence mechanisms, and described the soil mineralization, nitrification and denitrification characteristics and obtained the optimum curve fitting function, as well as stable incubation time for different land uses. Finally, the fitted parameters of the model using physico-chemical properties were predicted. The main results were listed as follows:(1) The study found that, for different land uses, soil accumulated mineralized nitrogen had large difference (paddy soil>vegetable soil>wasteland soil>forest soil>tea garden soil) within 28 days incubation experiment. The accumulated mineralized nitrogen of paddy soil was the highest (219.27 mg/kg). Rapid nitrogen mineralization rate mainly appeared within 7 days, and finally stable in the 28th day. Both single nitrogen pool model and two nitrogen pool model fitted the soil nitrogen mineralization well. Potential mineralized nitrogen calculated from the two kinds of model related significantly to soil total nitrogen, soil microbial biomass carbon, soil microbial biomass nitrogen, pH and alkaline hydrolysis nitrogen. Then, the functions for the parameters (potential mineralized nitrogen and mineralization rate constant) were established well using soil microbial biomass carbon and pH. Meanwhile, MBC played a more significant role in estimation of soil nitrogen mineralization dynamics parameters.(2) The study found that, for different land uses, soil accumulated nitrification nitrogen had large difference in 28 days incubation (vegetable soil> tea garden soil> wasteland soil >paddy soil> forest soil), and the accumulated nitrogen concentration of vegetable soil nitrification was the highest, and lowest in forest soil. The nitrification rate was slow within the initial five day, and then rapidly increased, which was perhaps due to the lower soil pH value. The 28-day incubation for soil nitrification tended to be unstable. The nitrogen nitrification rate related significantly to soil microbial biomass phosphorus and pH. Then, the predictive model for nitrification rate was established well using soil microbial biomass phosphorus and pH.(3) The study found that, soil accumulated denitrification nitrogen had large difference in 28 days incubation (paddy soil>vegetable soil>wasteland soil>forest soil>tea garden soil), the accumulated nitrogen content in paddy soil was the highest (330.83 mg/kg). Rapid nitrogen denitrification rate mainly emerged within 7 days incubation, and stable in 28th day. First-order kinetic model fitted the soil nitrogen denitrification curve well. The potential denitrification nitrogen showed significant correlation with soil total nitrogen, soil microbial biomass carbon, soil microbial biomass nitrogen and alkaline hydrolysis nitrogen. Eventually, the model was developed well just only from soil microbial biomass carbon.