Review of soil nitrate formation, leaching transport and their control measures in upland farming systems

Figuring out how to improve nitrogen use efficiency and reduce nitrogen loss to abate its impact on environment in order to ensuring high crop yield production are of leading global research interest today. The leaching of nitrate is the main pathway of nitrogen loss and the main mode of regional groundwater nitrate pollution. It has become a severe agricultural and ecological environmental problem in intensive agricultural regions around the world. Thus it is important to understand nitrate formation, leaching process, influencing factors and to put forward effective control measures. A great number of studies have been carried out by both local and foreign scholars in this area that has led to the generation of abundant information over the years. In this paper, soil nitrification process driven by micro-organisms was briefly reviewed. The advantages and disadvantages of in situ nitrate leaching monitoring methods were compared. The factors that affected nitrate accumulation and leaching were also analyzed. On the basis of the above parameters, effective control measures were summed up and future research directions were suggested strengthening researches on key micro-organism processes, mechanisms and functions of relevant driving factors of nitrification of upland soils. These clear understanding on soil nitrogen would contribute to the critical basis for the optimization of nitrogen management and the development of technologies to control nitrate leaching in upland farming systems. The exploration and establishment of methods of reducing soil disturbance, simple maintenance, less sample pollution and suitable long-term in situ field monitoring was particularly crucial to accurately reveal the soil nitrate leaching and real-time flux. The systematic development of comprehensive studies on nitrate leaching in different upland farming systems, the clarification of various factors that affected nitrate accumulation and leaching, and then the putting forward of effective control measures based on actual field conditions were required to reduce the risk of nitrate leaching at regional scale.