Field Effect And Soil Safety Analysis Of Reuse Of Domestic Sewage Tail Rice Field

As a big agricultural country,China is currently facing a serious water shortage problem.The amount of domestic sewage in rural areas is huge.Although the sewage treatment technology has been greatly improved,the sewage treatment rate is still low.While developing agriculture in my country,there are also environmental problems and irrigation water problems.Among them,the nitrogen,phosphorus and other nutrients in agricultural wastewater are higher.Discharging it directly into the river will cause eutrophication and environmental pollution of the water body.Therefore,in the water network area of the southern plains of China,there was a good application prospect for using low-polluting water such as domestic sewage tailwater as an alternative water source for rice field irrigation.However,the rational application method of tailwater and the impact on rice growth and environmental safety are not sufficiently studied.In this study,a field experiment was used,with pond water without fertilization and conventional fertilization as the control group,pond water coupled with nitrogen fertilizer and domestic sewage tail water coupled with nitrogen fertilizer as the experimental group,to study the effect of rural domestic sewage tail water reuse on soil nutrients and physicochemical properties,rice growth and the impact on yield and soil safety of paddy fields.By measuring soil total nitrogen,total phosphorus,organic matter,microbial biomass carbon,microbial biomass nitrogen,soil enzyme activity,heavy metals,salinity,and rice aboveground biomass,yield and composition factors and so on.The comprehensive effect evaluation is carried out to obtain the optimal tail water reuse mode,which provides a scientific theoretical basis for ensuring soil health,preventing and controlling groundwater pollution,and effectively utilizing nutrients in urban sewage tail water.The main findings are as follows:(1)Soil organic matter,microbial biomass carbon,microbial biomass nitrogen and urease activity can be significantly increased after tailwater reuse and return to the field.Soil organic matter tailwater tiller-only fertilizer(STN),tailwater conventional fertilizer(SN),and tailwater reduced nitrogen fertilizer(SRN)increased by 1.04%,2.44%,and 11.19%,respectively,in 2019,2020,and 6.38%,6.62%,and 11.4%,respectively,compared to conventional fertilizer(CN)treatment in 2019;STN,SN,and SRN treatments increased by12.16%,10.59%,and 7.67%,respectively,in 2020,and increased by 12.16%,10.59%,and7.67%,and 6.38%,6.62%,and 11.4%,respectively,in 2021;STN,SN,and SRN treatments increased carbon by 27.85%,33.5%,and 34.75%,respectively,compared to CN treatment in 2019,and 23.3%,23.4%,and 14.43%;7.1%,10.46%,and 16.04% increase in microbial load of nitrogen in 2019 treatment STN,SN,and SRN,respectively,compared to CN treatment,The tailwater irrigation STN,SN,and SRN treatments increased by 15.9%,36.8%,and 46.88%,respectively,in 2021 compared to the CN treatment;the annual urease activity STN,SN,and SRN increased by 46.03%,34.92%,51.61%,and 2.01%,0.98%,and 2.94%,respectively,in 2019 and 2021 compared to the CN.The correlation analysis of soil physicochemical properties with microbial biomass and enzyme activity in 2021 showed that the correlation coefficients of organic matter with microbial biomass carbon and urease were 0.885 and 0.939,respectively,with significant positive correlation.Therefore,tailwater irrigation can improve soil nutrients and was conducive to the reproduction of soil microorganisms,and tailwater reuse will increase soil fertility to a certain extent,but in the reuse process,the tailwater should be used in an appropriate amount and in an appropriate manner according to the variability of tailwater quality.(2)Through field experiments,the effect of the combined nitrogen fertilizer application of rural domestic sewage tail water and pond water on rice biomass and material distribution,yield and treatment components was studied,tiller number,vegetation coverage rate(NDVI),plant height,total dry mass,number of ears,number of grains per ear,and yield and so on,all have promoting effects.In 2019,conventional tailwater fertilization(SN)and tailwater nitrogen reduction(SRN)compared with conventional irrigation and fertilization(CN),the yield increased by 8.54% and 6.28%.In 2021,STN,SN,and SRN increased by 13.99%,32.55%,and 17.7%,respectively,compared with CN treatment.The effect of tailwater irrigation is comparable to that of pond water coupled with nitrogen fertilizer.This shows that rural domestic sewage in the agricultural use of tail water has large potential,the dosage of the tail water irrigation farmland can not only save water resources,effectively reduce the environmental risk,also can ensure the normal order of the rice growth and yield,and indirectly,to save fertilizer input,to save water resources,improve the economic benefit has an important significance.(3)In this study,the detection results of the heavy metal content in the soil after harvest in the tailwater treatment group met the limit requirements of the "Soil Environmental Quality"(GB 15618-2018)standard,and under the tailwater irrigation,the soil heavy metal content and the concentration of medium and trace elements accumulated with the increase of the year,and the short-term impact was not significant,but long-term irrigation may have the risk of heavy metal accumulation.Soil salinity increased with the increase of depth,and the soil salinity SN increased by 7.92% compared with CN treatment in 2019,SN and SRN increased by 66.67 and 63.68% compared with CN treatment in 2020,SN in 10～20 cm soil layer increased by 37.66% compared with CN treatment in 2021,and the increase in tailwater irrigation treatment was higher than that of pond water irrigation,and it increased at 0～30cm.Therefore,long-term field tests should be conducted to determine the risk of heavy metal and salt accumulation in tailwater irrigation to ensure the soil safety of tailwater reuse.In summary,domestic sewage tailwater irrigation paddy fields can not only have a certain yield increase effect,but also improve soil nutrients,reduce the amount of chemical fertilizer applied,significantly improve the agronomic efficiency of nitrogen fertilizer,shortterm tailwater irrigation will not cause soil heavy metal pollution and salt accumulation,but its long-term effect needs to be paid close attention to.The benefits of tailwater reuse farmland outweigh the disadvantages and were worth applying to irrigation of rice fields or farmland.