Study On Reducing Cd Pollution In Vegetable Fields By Mixing Soil Conditioner And Leaf Surface Inhibitor Under Rotation System

Chinese soil heavy metal pollution is serious,and cadmium is the first heavy metal pollutant in soil.At present,phytoremediation is the mainstream direction for remediation of heavy metal contaminated soil at home and abroad.However,the simple use of phytoremediation not only has low remediation efficiency and long remediation cycle but also requires the soil to stop farming.Therefore,it is necessary to use the model of super-accumulated plants and cash crop rotation restoration to improve the phytoremediation,so as to achieve the win-win goal of remediating Cd polluted farmland and obtaining economic income.This strategy can be widely used in the soil contaminated with low concentration of heavy metal pollution.Through the diversity of plant planting,the safety of agricultural products can be guaranteed,and the purpose of gradually repairing heavy metal contaminated soil can be realized.In this experiment,Amaranth,a Cd super-accumulation plant,and lettuce as cash crop were selected as rotation plants by taking soil with different Cd pollution concentrations as the research objects.Different concentrations of citric acid,and different concentrations of water-soluble fertilizers containing humic-acids were sprayed to the soil of amaranth in the rotation system,and different concentrations of water-soluble fertilizers containing humic-acids were sprayed on the foliar surface of lettuce,in order to explore the optimal concentration of citric acid for the remediation of different Cd contaminated soils and the optimal spraying concentration of water-soluble fertilizers containing humic-acids for foliar spraying.The effects of crop rotation system on lettuce growth and Cd contaminated soil remediation were observed,in order to ensure farmers’income and soil remediation efficiency,improve the acceptance of local farmers to phytoremediation,and also provide a theoretical and practical basis for promoting the application of amaranth rotation to restore Cd contaminated cultivated land.The results are as follows:（1）The application of citric acid could increase the p H,OM content and CEC of amaranth soil,with the maximum increases of 0.2、1.43mg·kg^-1、1.46cmol·kg^-1,which would also promote the conversion of soil Cd from reducible and residual state to acid extractable and oxidizable state.（2）The application of citric acid could increase the chlorophyll content of amaranth plants,thereby increasing its biomass.The maximum increase in chlorophyll is0.27mmol·kg^-1.As a soil activator,citric acid can also increased the accumulation of Cd in the aboveground and underground parts of amaranth,with the maximum increases of6.01mg·kg^-1and 3.59mg·kg^-1.（3）The application of citric acid increased the accumulation of Cd in polluted soil by amaranth,thereby increasing the enrichment coefficient and remediation rate of polluted soil,with the maximum enrichment coefficient being 25.59 and the highest remediation rate being 30.46%.（4）The spraying of water-soluble fertilizers containing humic-acids can increase the p H,OM content and CEC of lettuce soil,with the maximum increase of 0.12,0.86g·kg^-1and 3.87cmol·kg^-1,which will also reduce the DTPA-Cd content in the soil after planting lettuce,and promote the transformation of soil Cd from acid extractable and oxidizable state to reducible state and residue state.（5）The spraying of water-soluble fertilizers containing humic-acids could increase chlorophyll content of lettuce,protect photosynthesis from damage,and thus increase the biomass of lettuce plants.The maximum increase of 0.21mg·g^-1,which could inhibit the transfer of Cd in soil to the upper ground and also reduced the accumulation of aboveground Cd of lettuce,the maximum decrease was 0.089mg·kg^-1,and the accumulation of underground Cd of lettuce was 0.133mg·kg^-1.（6）In the amaranth-lettuce rotation system,applying citric acid to amaranth soil will promote the accumulation of Cd in contaminated soil by amaranth,and spraying water-soluble fertilizers containing humic-acids to lettuce leaves will inhibit the transfer of Cd in contaminated soil to the upper ground,ultimately achieving a win-win situation of"efficient remediation and safe production".the optimal application amount of citric acid in Cd0.5 treatment is 5mmol·kg^-1,the optimal spraying amount of water-soluble fertilizers containing humic-acids is 0.1g·kg^-1,the optimal application amount of citric acid in Cd3treatment is 10mmol·kg^-1,the optimal spraying amount of water-soluble fertilizers containing humic-acids is 0.15g·kg^-1,the optimal spraying amount of citric acid in Cd5treatment is 15mmol·kg^-1,and the optimal spraying amount of water-soluble fertilizers containing humic-acids is 0.2g·kg^-1.