Effect Of Nitrogen Application Levels On Ammonia Volatilization And Its Mechanisms In Typical Double Cropping Paddy Field Of Southern Hills Region

We studied on response of ammonia volatilization to nitrogen (N) application levels using closed continuous airflow method in typical double cropping paddy field in Southern Hills region, and effecting factors of ammonia volatilization and threshold value of N fertilizer application were then analyzed. The results were showed:(1) Ammonia volatilization is one of the most important approaches of N losing in paddy field. The amount of ammonia volatilization was65.67±1.56kg·hm-2by optimized N application (150kg·h-2) in early rice field, accounted for39.8%of N application, and was94.42±2.32kg·hm-2by optimized N application (180kg·hm-2) in late rice field, accounted for46.9%of N application. There was a significant exponential relationship between ammonia volatilization and amount of N application; Ammonia volatilization dynamic under different N levels were exhibited the similar regular:the ammonia volatilization flux reached peak within1-3days after fertilization in double paddy field, then declined and approached the level of CK treatment. The ammonia volatilization rate was showed:late rice> early rice; dressing> basal in early rice, and reverse in late rice.(2) There is a significant effect of NH4+-N concentration and pH in surface water on ammonia volatilization, both of them can improved significantly by nitrogen fertilizer application. The ammonia volatilization fluxes were significant positively correlated with NH4+-N concentration and pH value in surface water; Temperature and thickness of the surface water was an important factor affecting ammonia volatilization. The raise of surface water temperature and reduce of the water thickness has a direct result of NH4+-N concentration in surface water, promoted the occurrence of ammonia volatilization. The affect is mainly concentrated in the period of high NH4+-N concentration;Air temperature, rainfall and other climatic factors has a great impact on the ammonia volatilization, Low temperature and heavy rainfall will inhibit ammonia volatilization and its transfer. (3) The rice yield has a significantly response to N application to fitting quadratic parabolic equation in Hunan double-crop rice area; Volatilization rate of ammonia was increased and use efficiency of N fertilizer was decreased corresponding with increasing of N application level.(4) Based on the considerations of the both of the food security and environmental safety, we recommend the ecological threshold of N fertilizer application in Hunan province were93.18-177.63kg·hm-2in early rice and166.95-218.03kg·hm-2in late rice, respectively.