Effects Of Different Irrigation Levels Of Reclaimed Water On Soil Quality And Distribution Of Soil Pathogens

As the increasing contradiction between supply and demand of water resources,agricultural utilization of reclaimed water as an alternative to water resources has attracted more and more attention.This paper mainly studied the effects of different irrigation levels of reclaimed water on soil quality and distribution of pathogenic bacteria,in order to provide theoretical basis for rational utilization of reclaimed water and achieving soil environmental quality and safety of reclaimed water irrigation.In this study,soil physical and chemical properties,enzyme activities,heavy metals,microbial community structure and pathogenic bacteria contents in 0-60 cm soil layer under different treatments were measured and analyzed through indoor soil column irrigation experiments.The main results are outlined as follow:(1)The analysis of physical and chemical properties in soil showed that,irrigation with reclaimed water increased the content of soluble salt,total phosphorus and total nitrogen,but had no significant effect on soil pH.Compared with deficient irrigation,full irrigation with reclaimed water significantly increased soil total phosphorus content and deep soil salinity content,the difference of soil nitrogen content under two irrigation levels of reclaimed water was greatly affected by irrigation time limit,and the total nitrogen content of each treatment increased first and then decreased with the increase of irrigation time.There was no significant difference between two irrigation levels of reclaimed water in soil pH.(2)The analysis of enzyme activity in soil showed that,under the same irrigation level,reclaimed water irrigation increased urease and invertase activities in some soil layers compared with tap water irrigation.In the early stage,reclaimed water irrigation had no significant effect on soil catalase activity.After 300 d,full irrigation of reclaimed water significantly increased catalase activity in deep soil.The comparative analysis of two irrigation levels of reclaimed water showed that,there was no significant difference in soil urease activity between the two irrigation levels in the early stage,and urease activity in some soil layers of full irrigation treatment was significantly increased after 300 days compared with that of inadequate irrigation treatment.Compared with inadequate irrigation,early full irrigation of reclaimed water significantly increased catalase activity in deep soil.After 300 days,there was no significant difference in catalase activity between two irrigation levels.(3)The analysis of heavy metals in soil under different treatments showed that,reclaimed water irrigation increased the content of heavy metals in some soil layers,and the content of Cd in surface soil increased significantly at higher irrigation level.Although the contents of heavy metals(Cd,Pb,Cu,Zn)in soil under reclaimed water irrigation have been increased to some extent,according to the soil environmental quality standard risk control standard for soil contamination of agriculture land[GB15618-2018],soli after irrigated by reclaimed water did not exceed the standard.Therefore,reclaimed water irrigation could not cause soil heavy metals pollution.The results of comparative analysis of different irrigation levels of reclaimed water showed that,the contents of Cd in surface soil was increased by full irrigation compared with inadequate irrigation.The two irrigation levels of reclaimed water had little effect on the contents of Pb and Zn.(4)Compared with tap water,reclaimed water irrigation reduced soil microbial community diversity and OUT number at 97% similar level,full irrigation of reclaimed water reduced deep soil microbial community diversity and microbial species number compared with deficient irrigation.The main bacterial groups in different treatments were actinomycetes and metamorphic bacteria.Reclaimed water irrigation promoted the growth of soil actinomycetes and inhibited the growth of proteus under both full and deficient irrigation.Compared with deficient irrigation,full irrigation of reclaimed water promoted soil actinomycetes and Proteus,and inhibited soil curvularia,acidobacteria and phytoplasma.The higher the irrigation level of reclaimed water,the more favorable the growth of dominant bacteria in soil.Principal component analysis showed that the metabolic functions of soil microbial communities were different under different treatments,and the aggregation forms of soil microbial communities were different under different principal components.The functional composition of COG in soil samples under different treatments was similar.The major functional abundances were amino acid transport and metabolism,general functional prediction,energy production and conversion,unknown functional species.KEGG metabolic pathway abundance analysis showed that membrane transport,carbohydrate metabolism and amino acid metabolism accounted for the largest proportion of microbial metabolic pathways in all treatments.Full irrigation with reclaimed water can significantly promote membrane transport,carbohydrate metabolism and amino acid metabolism of microorganisms in surface soil.(5)Distribution of soil pathogenic bacteria in different treatments showed that,short-term reclaimed water irrigation significantly increased the number of soil thermotolerant coliforms at the same irrigation level,but there was no significant difference in deep soil after long-term irrigation.In early stage,the number of thermotolerant coliforms in surface soil under two irrigation levels of reclaimed water was significantly different.The difference of the number of thermotolerant coliforms in surface soil between full irrigation and deficient irrigation decreased gradually after long-term irrigation,and there was no significant difference in most soil layers.The number of thermotolerant coliforms in surface soil decreased gradually with the increase of time,and the number of thermotolerant coliforms in deep soil first decreased and then increased.