Migration And Transformation Mechanisms Of Chemical Nitrogen In The Soil Of Rainfed Study

We chose the spring maize-soil system in Yanqing county as our study object, studied the transformation, the dynamic variation and the source and sink of the nitrogen fertilizer in the soil, meanwhile measured the dynamics and the leaching losses of all the soil nitrogen pools, analyzed the recovery, residual and the losing pathway of nitrogen fertilizer, furthermore indicated the nitrogen losses and residual in the high nitrogen application rate. It will be helpful to effectively control the non-point pollution in the rural area, and it also can figure out a feasible nitrogen application rate and method for the constitutors and executors concerning the nitrogen management in the economic and environmental areas.The main conclusions obtained from our field experiment and the indoor experimental analysis showed as below:(1) The NH₄⁺-N concentrations were low and varied little between the different nitrogen application rates and the different soil layers in the whole spring maize growing period, and so it didn't need to consider the NH₄⁺-N concentration when dressing the nitrogen fertilizer in the future. The NO₃^-N concentration of soil in the growing period was easily lost by leaching. The transformation and flow of nitrogen fertilizer in the crop-soil system were measured by ¹⁵N tracer method, and the results showed that the losing part of nitrogen fertilizer in the experimental field were great, which would increase with the increase of the nitrogen application rate, and the leaching nitrogen would even arrive at 200cm soil layer. The fertilizer nitrogen was an important source for the soil NO₃^- -N, this indicated that, most of the NO₃^- -N presented in the soil was resided by the traditional dressing fertilizer method, and the groundwater maybe was primarily polluted by the NO₃^- -N.The soil microbial nitrogen varied evidently with the season, and the concentration of soil microbial nitrogen increased with the increment of nitrogen application rate, which indicated that the microbial nitrogen could modulate the process of soil nitrogen supply.(2) The yields, biomasses and the nitrogen accumulations of spring maize were all increased compared between the dressing nitrogen fertilizer treatment and the non-dressing nitrogen treatments, which were also increased with the increment of the nitrogen fertilizer application rate, and it would come to a static state. This indicated that the nitrogen fertilizer applied to the soil only partly absorbed by the spring maize,...