Estimation of N loss loading by runoff from paddy field during submersed period in Hangjiahu area
杭嘉湖地区淹水稻田氮素径流流失负荷估算

As the largest bread basket in Zhejiang Province, Hangjiahu area is facing more and more serious water pollution, while the N loss loading by runoff from the paddy field during its submersed period is the main cause of the pollution. Through field experiment and fixed spot observation, the model of precipitation - runoff in Yangtze delta was testified, and the results showed that the precipitation - runoff model from HE Baogen was basically accorded with the fact after considering the impact of field overflow mouth, and the error was between - 19. 9% and + 18. 0%. The model of N concentration with precipitation - runoff in paddy field during submersed period was brought forward, with the R value being 0. 948. These two models consisted of the model of N loss loading by runoff from paddy field during submersed period. Based on this model as well as the past 30 years data of fertilization and precipitation, 1: 250,000 topography map, land use map, and water system map, the N loss loading and its distribution were estimated by using GIS method, and the results showed that the N loss loading was different from place to place, with an average of 35.26 kg N x hm(-2), and accounting for 12. 69% of the applied N. The N loss loading in Anji and Yuhang with obviously more precipitation was higher than that in other places, while Haining also had a serious N loss problem because of the huge amount of applied N.