Maize Growth And Heavy Metal Uptake In Mudflat Soil Amended By Sew Age Sludge And Sludge-based Vermicompost

The mudflat in the east coast of China can be used as an important reserve cultivated land resource,but it belongs to saline-alkali land and can only be used as agricultural land after it is fertilized and matured.Sewage sludge is rich in organic matter,nitrogen and phosphorus,which can be used as an important organic fertilizer source for the improvement of saline-alkali land.However,heavy metals contained in sewage sludge may lead to soil heavy metal pollution in the process of mudflat improvement.It is not clear whether earthworm composting can reduce the environmental pollution risk of heavy metals in the process of improving mudflat soil with sewage sludge.In this study,the effects of different earthworm inputs(0,20,40,60 g kg-1)on the character and heavy metal morphology of sewage sludge were investigated.The effects of different application rates(0,0.5%,1.0%,1.5%,2.5%)of sewage sludge and sludge vermicompost on maize growth and heavy metal accumulation were studied by pot experiment.The results showed that:(1)The earthworm composting decreased pH value,EC,content of organic matter,total nitrogen,and increased the content of total phosphorus,alkali-hydrolyzed nitrogen and available phosphorus in sewage sludge.Earthworms showed a biological enrichment effect on heavy metals for Cd,Cr,Cu,Mn,Ni,Pb and Zn in sewage sludge.After composting with earthworms,the content of Cr and Pb in sewage sludge decreased,the content of Cu,Mn and Zn increased,while the Cd content has no significant change.The earthworm composting increased available Cd,Cu,Mn content in sewage sludge,but increased the proportion of residue Cr,Cu,Ni,and Pb.(2)The application of sewage sludge and sludge vermicompost improved significantly the properties of the mudflat soil.With the increasing of the application amount of sewage sludge and sludge vermicompost,the pH value of mudflat soil showed a gradually decreasing trend,and the content of organic matter,total nitrogen and phosphorus,alkali-hydrolyzed nitrogen and available phosphorus showed a gradually increasing trend,while the soil EC showed a increasing trend.Under the condition of equal carbon content,the contents of total nitrogen,alkali-hydrolyzed nitrogen and total phosphorus in soil treated with sludge vermicompost were generally higher than that of sewage sludge treatment.(3)The application of sewage sludge and sludge vermicompost increased the heavy metal contents in the mudflat soil.With the increasing of the application amount of sewage sludge,the total amount of Cd,Cu,Mn,Ni,Pb and Zn in the mudflat soil increased signifi cantly,the contents of available Cd,Cu,Mn,Ni and Zn increased significantly,and the proportion of residue Pb increased.With the increasing of the application amount of sludge vermicompost,the total amount of Cu and Zn increased significantly,the contents of Cd,Cr,Cu,Ni and Zn increased significantly,and the proportions of residue heavy metals decreased.Under the condition of equal carbon content,the contents of Cr,Mn and Pb in the mudflat soil treated with sludge vermicompost were generally lower than those treated with sewage sludge.(4)The application of sewage sludge and sludge vermicompost incerased significantly plant height and dry weight of maize,and increased the content of heavy metals in maize plant.The contents of Cd,Cu,Zn,Cu,Mn in maize root,Cu,Mn in maize stem and Cd,Cu,Mn and Zn in maize leaves increased with increasing of the application amount of sewage sludge.With the increasing of sludge vermicompost,the contents of Cu and Mn in maize root increased significantly,the contents of Cd,Cu,Ni,Pb and Zn in maize stem and Cd,Cu,Mn and Zn in maize leaves showed an increasing trend.The contents and enrichment coefficients of Cd,Cr,Cu,Ni and Pb in maize root treated with sludge vermicompost were generally lower than those treated with sewage sludge,and the transfer coefficients of Cd,Cr,Cu,Ni and Pb were generally higher than those treated with sewage sludge.