Study Of Biochar On Remediation Of Cd Pollution In Acidic Paddy Soils

At present,China's farmland soil heavy metal pollution is increasingly serious,excessive cadmium content of rice,food safety has aroused our concern.Passivated repair technology has the advantages of low cost,quick effect and simple operation,and has wide applicability.In this paper,the effects of biochar on Cd available and Cd distribution,soil pH,four enzymes(catalase,alkaline phosphatase,invertase and urease activity)and the content of Cd in various parts of rice were studied by rhizosphere box experiment.The field experiment was conducted to study the effect of microbial fertilizer,organic fertilizer and peptide bio-organic fertilizer,bio-carbon,montmorillonite,coarse whiting and calcium magnesium phosphate treated with biochar respectively to soil physical and chemical properties(available phosphorus,available potassium,alkaline hydrolyzable nitrogen,pH value,organic matter and CEC),soil available Cd content,Cd content of rice parts(roots,stems,leaves,rice husk and soil)and rice yield.The main findings are as follows:The rhizosphere box experimental results showed that soil pH value has a rising trend with the increasing proportion of biochar.The available forms of Cd were declined under different dosages of biochar in rhizosphere and non rhizosphere soil,with the maximum reduction of 13.9%under the treatment of 50 g kg-1 biochar in rhizosphere soil.Cd concentrations in the first and second layer in non-rhizosphere soil were significant decreased under the dosage of 100 g·kg-1 biochar,resulting in27.4%and 22.9%reduction,respectively in contrast to the control,but for available Cd concentration in the third layer of non rhizosphere soil,it was significantly declined under the middle dosage of 50 g·kg-1 biochar,and decreased by 29.2 compared with CK.The application of biochar reduced Cd accumulation in different parts of rice.There was a significant difference(P<0.05)in root and rice under the content of 50 g·kg-1biochar compared with control treatments,and dropped by 49.8%and 81.2%respectively.The maximum reduction of 28.2%and 47.1%in Cd concentrations in the leaf and rice husk was got under the dosage of 100 g·kg-1 and 50 g·kg-1 respectively.The changes of Cd forms in rhizosphere and non rhizosphere soil are basically same after applying biochar.The contents of exchangeable fraction decreased significantly,the contents of carbonate-bound Cd and Fe-Mn oxides-bound Cd reduced slightly,while the contents of organic-bound Cd and residual Cd were increased,and residual Cd was notablly increased.The content of exchangeable fraction in rhizosphere soil was significantly higher than that of the non rhizosphere soil.Four kinds of enzymes activities(catalase,alkaline phosphatase,invertase,urease)in rhizosphere and non rhizosphere soil were all enhanced after applying biochar,and four kinds of enzymes activities all reached the maximum under dosage(50 g·kg-1)of biochar.And four kinds of enzymes activities of rhizosphere were generally higher than that of non rhizosphere.The field experience results showed that different passivating agents can reduce the available Cd content in the soil,and the decrease increases with the increase of the amount of passivation agent.The application of five passivating agents could increase the pH value of the soil.The content of CEC in the soil decreased with the addition of organic manure combined with bio-organic fertilizer and bio-carbon treatment,and the contents of CEC in soil treated with different amount of passivating agent were increased in different degree.The contents of available N and available P in soil were increased after adding five groups of passivating agents,respectively.In addition to the reduction of soil organic matter and available potassium content from montmorillonite and biochar treatment,the treatments of soil organic matter and available potassium were improved in different degrees.Different passivation materials have a certain effect on rice production.The content of Cd in different parts of rice could be reduced by different passivants,and the content of Cd was root>stem>rice husk>fine rice.The content of rice in edible parts decreased to 0.2 mg/kg(safe food standards).