Abstract: This study provided a basis for the prevention and control of agricultural non-point source pollution in paddy fields by studying the characteristics of nitrogen loss from drainage and drying of paddy fields and runoff in rainy seasons. For the test field with separate irrigation and drainage, the designed fertilization amount is 0, 90, 150, and 270 kg/hm² in turn. By monitoring the field surface water level during rice growth, daily rainfall, and the three nitrogen concentrations in the field surface water of each test plot before drainage and after rainfall, the law of nitrogen loss in different rainfall periods after drainage and drying and fertilization is proved, and the amount of nitrogen loss is estimated. The results showed that the nitrogen concentration in the runoff of paddy field was mainly related to the amount of fertilizer applied and the time interval between rainfall and fertilization date. The highest concentrations of NH₄⁺-N and TN in the three rainfall runoff were 12.000 mg/L and 13.520 mg/L respectively, of which NH₄⁺-N and NO₃-N were the main forms of TN loss; the total amount of TN loss generated by drainage and drying fields and rainfall runoff in the four test plots was 24.380 kg/hm², of which rainfall runoff was the main loss way. The amount of fertilization, rainfall runoff and the time interval between rainfall runoff and fertilization date are the main factors affecting nitrogen runoff loss.

Key words: paddy drainage, rainfall runoff, nitrogen, loss