| Confronted the severe environmental problem caused by traditional manage modes to water and fertilizer of farmland in the south of China, studying and formulating scientific and effective water and fertilizer management measures to control agricultural area pollution is a very urgent issue, which is great significance for improving agricultural production level and protecting the environment. Without the premise of reducing rice yield, how to use the appropriate fertilization technology, formulate reasonable times and amount of application, take reasonable irrigation and drainage measures to avoid excessive application of nitrogen fertilizer to reduce agricultural source pollution on the water environment, require take measures suitable for the local situation.The dynamic change characteristic of nitrogen on surface water of paddy field and the rice yield and output inscape and the nitrogen utilization efficiency and nitrogen balance under different nitrogen fertilizer application rates in experimental plots which in Yuyao, Zhejiang Province was studied in 2010.The target of this research is to provide technical indexes to control nitrogen loss in the paddy field and to protect water ecology and environment.The research results through the experiment indicated:(1) After urea application, there are more NH4+ than NO3- in the water surface of paddy field. The variation of NH4+ and TN is that it attained the biggest values in the first day after urea application, then gradually decreased influenced by the ammonia volatilization. The concentration of NH4+ and TN declined to as same as the plot without nitrogen fertilizer about a week after fertilizer was applied. The time which the peak of NO3- took place lagged behind NH4+ when N was applied for the reason of nitrification. The NO3- concentration reached the biggest ones in the third day after application, then went down. Taking into account a large area of paddy field were applied urea fertilizer in China, NH4+ and TN were the mostly important nitrogen indexes to monitor the water pollution in the paddy-field, NO3- may be the assistant nitrogen index. The dynamic change of three kinds of nitrogen in the surface water indicated that the concentration of three kinds of nitrogen was higher in the first 7days after urea application, and the water layer was deeper. If the heavy rain took place, the ground flow easily produced and brought the nitrogen away from the field. So these seven days after application was the critical time to prevent the nitrogen loss. There was an positive relationship between the concentration of nitrogen in the surface water and N application amount. Therefore, it is useful to decrease nitrogen application amount or even with N application in split time so as to decrease the N loss and leaching in the paddy-field.(2) Data analysis through the experiment show that the increase in a certain range of nitrogen fertilizer can increase plant height, tiuxsui length and grain numbers per tiuxsui, and promote tiller number, increase tiuxsui numbers per acre, However, when the excess N fertilizer reaches its limit, the blighted grain rate increased, The panicle seed setting rate and 1000-grain weight decreased, the quality of rice degrade. In a certain range of nitrogen fertilization can increase rice yield, but more nitrogen will lead to production decline. The quadratic trinomial function y =-0.03x2 +11.63 x +6168.29 fitted the relationship of rice yield and nitrogen fertilizer quite well, the correlation coefficient was 0.9487. According to Fertilizer Effect Function Method, when the yield obtained highest , the amount of fertilizer application are 194 kg/hm2. It can reduce fertilizer than farmers more than 10%, but not decreased the yield of rice. The paper applied the principle of marginal cost and income in agricultural technology economics, the results show that when the nitrogen application rate was 167 kg/hm2, economic benefits is best, the corresponding yield was 7274 kg/hm2.Less than 167 kg/hm2, fertilizer cost is lower, but the fertilization rate of profit by a certain rate reduction. From lower costs, improve efficiency and reduce nitrogen loss risk considerations, the study area optimum amount of nitrogen should be 167 kg/hm2.(3) The analyses to the nitrogen-fertilizer use efficiency index show that a highly significant negative correlations between nitrogen efficiency for grain production and the amount of N uptake, the correlation coefficient was -0.970. The plant absorb too much nitrogen will decrease the nitrogen efficiency for grain production, so proper control of nitrogen uptake is a prerequisite for increasing the nitrogen efficiency for grain production.The rice recovery efficiency decreased with the amount of nitrogen increased, the change ranges between 21.12% and 45.75%. The nitrogen recovery efficiency showed a highly significant negative correlation with the amount applied fertilizer, the correlation coefficient was -0.751, while a significant positive correlation with the amount N uptake, the correlation coefficient was 0.914. Therefore, to improvefertilizer-nitrogen use efficiency , it is necessary to reduce the amount of nitrogenous fertilizer applied. The partial factor productivity of applied N also reduction with the amount of nitrogen increasing, changes in the range of 35.33 ~ 50.76 kg .kg-1. The partial factor productivity of applied N was significantly negative with the amount of N fertilizer applied, the correlation coefficient was -0.975. Physiological efficiency increased with the N fertilizer increasing, from 17.46 kg .kg-1 increased to 42.36 kg .kg-1, but decreased 20.51 kg .kg-1 when N fertilizer applied more than 195 kg/hm2. The physiological efficiency showed a highly significant negative correlation with the amount N uptake, the correlation coefficient was -0.897, while a significant positive correlation with the yield, the correlation coefficient was 0.699. The agronomic efficiency are very low in every plot, ranges from 5.3 kg .kg-1 to 8.2 kg .kg-1, because of high soil background value of nitrogen .(4) The paper calculated soil-plant nitrogen balance under different nitrogen fertilizer application rates by monitoring the soil, plant and irrigation water. The result shows that soil residual nitrogen in applied N plots are higher than without N applied plot, with the increasing amount of N fertilizer, residual nitrogen in the soil also increase. Nitrogen surplus is not absorbed by crops and residues in the soil and losses in the environment, With the increasing of nitrogen, nitrogen surplus increased significantly, and the surplus of nitrogen in applied N fertilizer plots were significantly higher than without nitrogen treatment. Therefore, in order to reduce the apparent residue and nitrogen loss, taking into account the capacity of nitrogen supply by the soil, reducing the amount of N application is necessary.
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