Study and experiment effect on the mitegating the pollution of drainage water form paddy field with Four Defense Lines System—Take Zhanghe irrigation system, Hubei province as an example

A large amount of nitrogen and phosphorus in discharged water form paddy field cause serious agricultural non-point source pollution in rice-based irrigation area. A “Four Defense Lines” system of water-saving irrigation, field grass ditches, pond wetlands and ecological trunk ditches to purify the water discharged form paddy field is proposed in this paper. Experiment on the effect of reducing the pollution of drainage water form paddy field with this system has been conducted in Zhanghe irrigation system, Hubei province, China. According to the result of the experiment, each subsystem under the “Four Defense Lines” mode is effective in reducing contamination, and the comprehensive system also has satisfactory effect on improving the water environment in paddy irrigation. The effects of reducing of total nitrogen, total phosphorus, ammonia nitrogen and nitrite nitrogen by comprehensive system are 92.3%, 82.8%, 94.4% and 64.6% respectively.