Effects Of Different Inorganic Fertilizer On Immobilization Remediation Of Cd Polluted Paddy Soil Using Sepiolite

Relevant statistics have showed that the total area of farmland polluted in our country is as high as2.3×107 hm².Among the heavy metal pollution,the Cd pollution in soil is particularly prominent.In China,Cd pollution in farmland soil poses a great threat to food security.How to safely and effectively restore and use these contaminated farmland soils has become an urgent environmental and social issue.The in-situ passivation repair technology is a kind of remediation method based on the purpose of reducing the risk of heavy metal pollution.Because it has the advantages of low repair cost,convenient operation,and good effect,it can be obtained in a wide range of applications at the treatment of medium and mild heavy metal Cd pollution farmland soil in China.Fertilization is an important means of increasing production and securing production in agricultural production.In the existing research on the rehabilitation of heavy metal pollution in the soil,the effects of applying fertilizers on the passivation and repair are often neglected.Different kinds of chemical fertilizers have a synergistic or antagonistic inhibitory effect on the passivation repair effect.In this study,rice/rape pot experiment was used to explore the application of different fertilizers on the recovery of Cd-contaminated farmland soil by the passivation of sepiolite.The aim is to provide reasonable theoretical basis for rational fertilization in the process of immobilization remediation,The main findings and conclusions are as follows:1.The rice pot experimental results showed,compared with flooded management and non-flooded water management,the exchangeable Cd concentration diethylenetriaminepentaacetic?DTPA?acid leaching was decreased significantly under the immobilization remediation of sepiolite.Compared with the immobilization remediation of sepiolite,the Fe concentration of dithionite-citrate-bicarbonate?DCB?leach liquor was decreased after adding urea by 39.61%⁵5.59%and 22.51%⁵3.63%under flooded and non-flooded management,respectively.Urea have a positive effect on soil Cd adsorption by root iron plaque under flooded management,but have negative effect under non-flooded management.The Cd concentration of root were increased by 36.11%⁷1.30%and 58.20%⁸9.42%under two water management.Compared with the immobilization remediation of sepiolite,under flooded management,the Cd concentration of brown rice have increased by 28.89%and 8.89%,after add low or medium dose urea.But the Cd concentration of brown rice have decreased 22.22%after added high dose urea.The brown rice Cd concentration have no significantly change after adding different dosage urea under non-flooded water management.The results showed that immobilization remediation had no obvious influence on soil microbial structure and distribution under different experimental conditions.2.The rice pot experimental results showed,adding sepiolite,calcium magnesium phosphate,sepiolite combined with calcium magnesium phosphate,and sepiolite combined with calcium superphosphate significantly decreased the Cd uptake of plants.The Cd concentration of brown rice was reduced by 32.66%,36.53%⁶0.32%,30.62%⁶1.86%,and 26.45%³6.67%,respectively,using the additives listed above.The Cd concentration of shoots was reduced by 38.89%,49.77%⁶5.75%,49.36%⁷4.23%,and 35.81%⁶0.68%,respectively.Compared with the control,applying sepiolite,the two phosphate fertilizers,and sepiolite combined with the two phosphate fertilizers all significantly decreased the and DTPA-extractable Cd concentrations.The superoxide dismutase,peroxidase,and catalase activities in the roots of the control samples were higher than those for other treatments;the same was true for the malondialdehyde concentration and metabolites such as glutathione and non-protein thiol.Microbial community diversity and structure analysis showed that the fifteen most abundant microbial phyla in different treatments were roughly similar.3.The rape pot experimental results showed,the biomass of rape was significantly increased after the application of KCl and K₂SO₄,compared with alone sepiolite treatment.The Cd concentrations in shoot were increased by 16.38%⁶0.73%and 15.62%²5.19%,respectively.KCl and K₂SO₄ had limited effects of soil pH values,but increased the exchangeable Cd concentration significantly by25.51%³4.65%and 18.5%²4.96%,respectively.Sepiolite could make the Zeta potential of soil samples shift to the negative direction,but the addition of KCl and K₂SO₄ could make the Zeta potential of soil samples increase.KCl and K₂SO₄ could reduce the sorption amounts of Cd on sepiolite,and the maximum sorption amounts were reduced to 2.87 mg·g^-11 and 4.92 mg·g^-1 respectively.The bioavailable fractions of K,Mn,Cu and Zn were enhanced significantly by KCl and K₂SO₄.4.The results showed that the Cd content in brown rice/rape is the main inspection index,and in the process of repairing Cd-contaminated soil by sepiolite passivation,the effect of applying urea,calcium magnesium phosphate,calcium superphosphate and K₂SO₄ on the passivation will not be significantly effective.KCl has obvious adverse effects,which has reduced the immobilization remediation effect of sepiolite.