| In recent years,due to the continuous increase in industrial production,transportation and solid waste emissions,the problem of cadmium?Cd?pollution in China's farmland has become increasingly serious.Cd pollution in farmland soil has caused widespread concern about food safety.In order to make full use of farmland and control the health risks,this thesis screens out safe and low Cd accumulating crops and varieties on mild to medium Cd-contaminated soil(0.28 to 0.58 mg·kg-1).Furthermore,6 kinds of passivation agents,6kinds of rice and 3 rapeseeds with low Cd accumulation were selected,and the passivation agent with the best passivation effect was screened.The influence of the passivation agent on the physical and chemical properties of the soil was discussed.The objective of this thesis was to propose a method for ensuring the safe production of rice and rapeseed on mild to medium Cd-polluted farmland soils in Zhejiang Province,and to achieve the purpose of production while repairing.The main research contents and results are as follows:?1?Varieties of 42 rice,26 pakchoi and 171 rapeseed were selected to be planted infield plots.After the crops were harvested,Cd concentrations in different parts of the crops were determined.The results showed that Cd concentrations in the rice varieties of Zheliangyou274,Shaonuo 9714 and Jia 58 and the Chinese cabbage variety Degaoxia Green and Black Leaf Short Green were lower than the national food pollutant limit GB 2762-2017(?0.2mg·kg-1).These crop varieties could be selected as the low-Cd accumulating crops.The Cd accumulation in the stems and leaves of vegetables are higher than those in fruits and roots.Cd concentration in rapeseed is stem and leaf>root>rapeseed pod>rapeseed seeds.The rate of Cd content exceeding the standard was only 27.49%.It indicated that it was safe to plant rape on the soil with low Cd pollution.Planting rape and vegetables in farmland polluted can reduce Cd content in soil by 5‰every year.Therefore,the continuous cropping model of rice-rape or rice-vegetable with low Cd accumulatiing varieties can be adopted to enable the production while repairing.?2?In order to ensure the safety of crop production,the field plot experiment was carried out on the medium and light Cd polluted soil(0.28?0.58 mg·kg-1)with low Cd-accumulating crop and passivators.Six rice varieties with high yield?Xiushui 134,Jiahe 218,Jiahe 58 of conventional rice varieties,and Yongyou 9,Yongyou 12,Chunyou 84 of hybrid rice varieties?,three rape varieties?Zheyou 50,Zheshuang 72 and Zheyouza 1?and passivators?calcium magnesium phosphate fertilizer,straw,diatomite,silkworm organic fertilizer,organic carbon fertilizer and animal bone meal?were choosed in this study.After the application of different passivators,the Cd concentrations in the seeds of different varieties of rice and rape were detected.The results showed that the treatments of fertilizer containing Ca,Mg and P and silkworm sand organic fertilizer had good passivation effects on Cd in the soil planted with conventional rice.The passivation effect of Cd was as high as 43.75%-75%.The concentrations of Cd in rice met to the national standard?GB 2762-2012?safety limit value(0.2 mg·kg-1).Application of fertilizer containing Ca,Mg and P and silkworm organic fertilizer had the best effect on soil Cd passivation,the passivation effect was 76.27%and61.02%respectively.The concentration of Cd in rape seeds was within the safety limit(0.2mg·kg-1),and it was the lowest among all treatments.Therefore,the combination of conventional rice?Jiahe 58,Jiahe 218 and Xiushui 134?,or rape variety Zhesheng 72 with passivator?silkworm organic fertilizer or calcium magnesium phosphate fertilizer?could ensure the safety of rice and rape production.?3?In order to further explore the effect of passivator on soil p H,CEC,organic matter and forms of Cd in soil,a control group without any passivator and five treatment groups:Ca Mg P fertilizer,straw,silkworm sand organic fertilizer and organic carbon fertilizer were applied in pot experiment.to The results showed that the application of four kinds of passivators could increase the content of organic matter and the cation exchange capacity of the soil,thus promoting the transformation of soil Cd ditto the oxidizable form and residueform.The correlation coefficient of soil p H and organic matter with the available Cd?weak acid extraction?concentration was-0.879 and-0.725 respectively.There was no significant correlation between the available Cd concentration and CEC.The results showed that the p H and organic matter content of soil could be increased by adding passivator,and thus the availability of soil Cd was reduced.Application of Ca,Mg,P fertilizer and silkworm organic fertilizer were the most effectiveon passivating Cd.Soil p H was increased to 7.47 and6.06 respectively by the application of Ca,Mg,P fertilizer and silkworm organic fertilizer,and the organic matter content was increased by 10.45%and 8.35%respectively,meanwhile,the passivation rate of Cd reached 66.7% and 133.3% respectively. |
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