Effects Of Reclaimed Water Irrigation On Pollutant Emission From Paddy Field And Soil Properties

With the global water crisis becoming more and more serious,water recycling has become an important means to alleviate the lack of water resources.Reclaimed water is a kind of unconventional irrigation water,which can effectively alleviate the difficulty of agricultural water use,but it will also bring pollution and other problems.Therefore,taking rural domestic sewage as irrigation water source and rice as the research object,this paper studied the discharge law of pollutants（NH₄⁺-N,NO₃^--N）in paddy field under different irrigation modes of reclaimed water（mainly including surface runoff and leakage）,and studied the soil fertility change under reclaimed water irrigation by soil organic matter and soil nutrient element residues The main conclusions are as follows:1.The concentrations ofNH₄⁺-NandNO₃^--Ndecreased with time,and the nitrogen loss was concentrated at tillering stage,jointing and booting stage.Surface water is the main way of pollutant emission,andNH₄⁺-Nis the main form of nitrogen loss.Water source had significant effect on nitrogen loss in paddy field,but irrigation mode had no significant effect on nitrogen loss in groundwater.2.There was no significant difference in the content of nitrogen and organic matter among different soil layers.Reclaimed water irrigation did not change the content and distribution characteristics of soil nitrogen and organic matter,but high water level irrigation increased the content of soil organic matter.Under the regulation of reclaimed water irrigation,the contents of TN,TP andNH₄⁺-Ndecreased,while the content ofNO₃^--Nincreased.The contents ofNH₄⁺-NandNO₃^--Nin soil were related to water quality,but the contents of TN and TP were not significantly affected by them.The response of irrigation mode to different nutrient elements was also different.Water level regulation had significant effect on soilNO₃^--Ncontent,but had no significant effect on other nutrient elements.3.Soil p H,water-soluble salt content and electrical conductivity did not change significantly with rice growth period.Reclaimed water irrigation did not significantly change soil p H,water-soluble salt content and electrical conductivity during rice growth period.However,compared with the soaking stage,the p H value of soil increased,the soil environment tended to be neutral,the water-soluble salt content decreased and the soil conductivity increased after rice harvest.Reclaimed water had no significant effect on soil salinization risk,but high water level irrigation would increase the water-soluble salt content during rice growth period,increase the risk of soil salinization.4.During the whole growth period of rice,due to the different absorption of heavy metals by rice roots,the contents of Cd and Pb in the whole soil increased,while the contents of Cr,Cu and Zn decreased.The distribution of different heavy metals in soil is also different.