Study On The Combined Control Of Exogenous Iron And Organic Materials On The Accumulation Of Heavy Metal Cadmium In Rice

Cadmium(Cd)is a highly toxic heavy metal elements,which is easy to be absorbed and enriched by plants and cause harm.As the largest basic food crop in China,rice is easy to accumulate Cd.How to treat farmland soil Cd pollution and reduce the accumulation of heavy metal Cd in rice is an important issue related to Chinese food safety production.Iron(Fe)is an essential trace element for plant growth and it is closely related to the migration and transport of Cd in the soil-plant system.The application of organic materials is an important measure to improve soil fertility and one of the effective measures to remediate heavy metal pollution.After organic materials are applied to the soil,the basic physical and chemical properties of the soil will be changed,which will inevitably affect the role of Fe in the soil.Therefore,in this study,through pot experiments,on the basis of exploring the effects of different exogenous iron on the accumulation of Cd in rice in contaminated soil,the combined effect of exogenous iron and organic materials on the accumulation of heavy metal Cd in rice was further studied.Below are key research findings The main findings are as follows:(1)Compared with the control,the addition of two kinds of exogenous iron can significantly reduce the Cd content of rice brown rice.Under the same addition,the Cd content of rice brown rice in the ferrous sulfate treatment group was lower than that in the ferrous chloride treatment group.In this study,the Cd content of brown rice in the ferrous sulfate treatment group was lower than the national standard Cd content limit of 0.2 mg/kg,among them,240 mg/kg soil(calculated as Fe)had the lowest Cd content in rice brown rice under ferrous sulfate treatment(S3),which was 0.14 mg/kg.The addition of two kinds of exogenous iron increased the Fe content in each part of the rice,and under the same addition amount,the Fe content in each part of the ferrous sulfate treatment group was higher than that of the ferrous chloride treatment group.There is a very significant negative correlation between Fe content and Cd content in various parts of rice.The increase of Fe content in rice plants inhibits the accumulation of Cd in rice.(2)Compared with the control,the addition of two kinds of exogenous iron significantly reduced the soil pH value and Eh value,and the addition of ferrous sulfate reduced it more significantly than ferrous chloride.The addition of two kinds of exogenous iron significantly increased the soil Fe2+content and the soil available Fe content,and the ferrous sulfate treatment group was higher than the ferrous chloride treatment group at the same addition amount.The addition of the two kinds of exogenous iron significantly reduced the soil available Cd content.Under the same addition,the soil available Cd content of the ferrous sulfate treatment group was significantly lower than that of the ferrous chloride treatment group.The addition of two kinds of exogenous iron significantly increased the content of Fe and Cd in the iron plaque of rice roots,and at the same amount of addition,the addition of ferrous sulfate increased the Fe and Cd content in the iron membrane of rice root surface more significantly than ferrous chloride.(3)Compared with the control group,the single application of organic materials significantly reduced the Cd content of rice brown rice,and the treatment of exogenous iron combined with organic material further reduced the Cd content of rice brown rice.When the addition amount of exogenous iron is the same,the Cd content of rice brown rice in each treatment group of exogenous iron combined with soybean cake is lower than that in the combined vermicompost treatment group.The Cd content of rice brown rice combined with soybean cake treatment(SGB)under 240 mg/kg soil with exogenous iron addition was the lowest,which was 0.13 mg/kg.Regardless of whether the organic materials were combined with exogenous iron,the Fe content in each part of the rice was significantly higher than that of the control,and the exogenous iron combined with soybean cake treatment increased the most.(4)Compared with the control,organic materials can reduce soil pH and Eh to varying degrees,regardless of whether they are combined with exogenous iron.Compared with the control,single application of organic materials significantly increased the soil Fe2+content and soil available Fe content at each growth stage of rice,and the combination of exogenous iron and organic materials further increased the soil Fe2+ content and available Fe content.When the addition amount of exogenous iron is the same,the soil available Fe content in the combined soybean cake treatment group is higher than that in the combined vermicompost treatment group.Single application of organic materials significantly reduced the soil available Cd content at each growth stage of rice,and the combination of exogenous iron and bean cake treatment further reduced the soil available Cd content at each growth stage of rice.The content of DTPA-Cd in soil in the treatment group of exogenous iron combined with soybean cake was lower than that in the treatment group of vermicompost during each growth period.(5)Compared with the control,no matter whether the organic materials are combined with exogenous iron or not,the aboveground biomass of rice increased.The biomass of the above-ground part of rice treated with exogenous iron combined with organic materials is generally higher than the treatment with vermicompost alone.However,only under 240 mg/kg of soil with external iron addition(calculated as Fe)combined soybean cake treatment(SGB)the aboveground biomass of rice was higher than that of single application of soybean cake treatment,and the increase was the largest compared with the control,which was 68.24%.Compared with the control,single application of organic materials significantly increased the content of Fe and Cd in the iron plaque of rice roots,and the treatment of exogenous iron combined with organic materials further increased the content of Fe and Cd in the iron plaque of rice roots,and with the increase of the amount of exogenous iron added.When the amount of exogenous iron is the same,the Fe and Cd contents in root membrane of the combined soybean cake treatment group are higher than those of the combined vermicompost treatment group.