Nitrogen Balance On Typical Watershed Of Purple Soil In Rainy Area Of West China

With the social economy developing, people increased the input of nitrogen, which include fertilizer nitrogen and the gas from burning industry fossil fuel, to the global ecosystem for high crop yield and quick development rate of economy, moreover the agricultural non-point pollution was more and more tempestuous, as a consequence leading to enough nitrogen exist in the ecosystem, and caused a lot of eco-environmental problems. Therefore, systematic study on the nitrogen balance budget and scientific management of nitrogen had a significant impact on region sustainable development, biodiversity and ecological environment protection.Through field survey and located monitoring, this research studied at Zancun watershed, which was on the central region of rainy zone of west China, systematically analyzed the ways of N input and output, and recognized the process mechanism of atmospheric deposition, ammonia volatilization, denitrification and surface runoff, etc, and quantified nitrogen surplus of the watershed. The main conclusions are as followed:(1)The wet deposition of atmospheric nitrogen (34.27kg N·hm-2·a-1) was predominant on atmospheric nitrogen deposition, and it had a percentage69.1%of total deposition nitrogen. Moreover, NH4+-N was the dominant nitrogen fraction, and rainfall was significantly negative correlation with the concentrations of NH4+-N, NO3--N, DON and TON. In addition, there was "dry and rainy seasons" characteristic on wet deposition of atmospheric nitrogen, that was to say, the nitrogen amount of atmospheric wet deposition in rainy season (May to October) was higher than dry season.(2)The dry deposition of atmospheric nitrogen was15.34kg N·hm-2·a-1, of which NH4+-N, NO3--N, DON and TON were37.0%、25.7%and37.3%, and it was30.9%of the total deposition of atmospheric nitrogen.(3)The amount of nitrogen in runoff was6893kg N-a-1, which mainly occurred during May to October, and the amount of August was the highest. Moreover, the amount of nitrogen in runoff presented that summer> autumn> spring> winter, and the amount in summer accounted for65.5%of the total, and the amount of different nitrogen fractions was observed in the following order:NO3-N>DON>NH4+-N. As a consequence, we found that the NO3--N, which was77.1%of the total nitrogen, was the main nitrogen fraction in runoff.(4)The amount of fertilizer nitrogen and ammonia volatilization in Zancun watershed were13494.6kg N·a-1and8199.0kg N·a-1. In addition, the amount of ammonia volatilization after fertilizing chemical nitrogen and organic fertilizer were1387.3kg N-a"1and8199.0kg N·a-1, which were14.5%and85.5%of the total ammonia volatilization respectively.Nitrogen surplus of Zancun watershed was12861.3kg N·a-1, which was equal to54.4kg N hm-2·a-1. In addition, atmospheric N deposition and chemical fertilizer nitrogen were the most important input processes, while the ammonia volatilization and surface runoff losses were the main forms of output. Both the atmospheric deposition and chemical fertilizer nitrogen were dominant factors to nitrogen surplus in Zancun watershed. Therefore, it is necessary to recognize the mechanism of nitrogen sources and exports in Zancun watershed through establishing the long term monitoring mechanism, moreover combine scientific application of nitrogen fertilizer and consummate fertilization technology, etc, to increase the utilization ratio of fertilizer, and reduce agricultural non-point source pollution, eventually maintain the landscape pattern of watershed ecosystem, protect the biological diversity and realize the region sustainable development.