| Due to the sedimentation of polluted air,sewage irrigation,unreasonable disposal of high heavy metal waste,and the extensive use of fertilizers and pesticides,farmland soil in the northern region has been severely polluted by heavy metal cadmium.The North China Plain is the main grain producing area in China.The main grain crops are wheat,corn,etc.Therefore,the quality of grain production such as wheat and corn has received widespread attention,and the remediation of cadmium contaminated soil is crucial.Previous studies have shown that in-situ fixation method is suitable for the remediation of mild or moderate cadmium contaminated soil.By applying fixatives to change the chemical form of cadmium or reduce the bioavailability and distribution of cadmium ions in soil and plants,it has the characteristics of high efficiency,time saving,strong operability,and low cost;Spraying foliar conditioners can inhibit the absorption of cadmium content in wheat grains by reducing the transport of cadmium ions to the edible parts.At present,a single remediation method has been proven effective,but there is still a lack of integrated comprehensive application research to form a feasible remediation plan that considers various factors such as cost,yield,actual investment,and soil remediation.This paper verified that sepiolite and iron oxide have the ability to adsorb and fix cadmium through isothermal adsorption experiments,and that leaf inhibitor rich in manganese,zinc and other elements can reduce the transport capacity of cadmium ions from wheat roots to stems and leaves through hydroponic wheat experiments;Sepiolite,iron oxide and foliar inhibitor were applied to the field experiment of two rotation patterns of Maiyu and Maiju to study their effects on soil cadmium fixation and remediation and food safety production;At the same time,based on the "Compilation of National Agricultural Product Cost Benefit Data 2021",the economic benefits generated by the two planting modes were calculated to identify the most suitable planting mode for promotion,providing theoretical basis and technical support for largescale promotion of field soil remediation.The adsorption mechanism of sepiolite and iron oxide in water was investigated by SEM-EDS characterization based on the investigation of isothermal adsorption.The results show that:(1)Isothermal adsorption shows that the adsorption of sepiolite and iron oxide corresponds to the Langmuir model,and the adsorption of sepiolite and iron oxide is mainly based on the single molecular layer adsorption on the uniform surface.The adsorption capacity of sepiolite and iron oxide increases with the increase in Cd concentration and tends to be flat after reaching the highest value.(2)The maximum adsorption capacity of sepiolite and iron oxide is 26.455 mg/g or 40.984 mg/g.The adsorption effect is good,and the adsorption process is gradually irreversible after the increase in the initial concentration.(3)SEM-EDS shows that the surface of the mineral adsorbed with cadmium ions is uneven,with a small amount of protrusions,and Cd crystals appear as granules on its surface.Further EDS analyses showed that the surface of mineral particles after adsorption contained not only elements such as Ca,Si,C,Fe,but also Cd.The field plot experiment was carried out in Dabizhuang Village,Dongli District,Tianjin City,where the cadmium pollution concentration in the farmland was moderate and even,to explore the inhibition and control effect of spraying leaf conditioners on the absorption and accumulation of cadmium in wheat,as well as the growth and production effect.By applying two passivating agents,sepiolite and iron oxide,the inhibition and control effect of two passivating agents on the absorption and accumulation of cadmium in wheat and the bioavailability of cadmium in soil were explored.At the same time,the safe production model of wheat maize and wheat chrysanthemum rotation was explored.The results showed that:(1)Under the wheat jade rotation mode,the blank treatment of wheat Jinqiang 9 and Jimai 22 had low Cd content in their grains,making them suitable for planting as low accumulation varieties;Spraying foliar conditioners can reduce the cadmium transport coefficient of wheat,thereby reducing the cadmium content in wheat grains and meeting safety standards.At the same time,it helps to improve the yield and thousand grain weight of some wheat varieties;Applying two passivators,sepiolite and iron oxide,can effectively reduce the content of available cadmium in soil,increase soil p H,affect the distribution of cadmium forms in soil,thus preventing and controlling the transport of cadmium from wheat stem and leaf to grain,and from corn leaf to grain,reducing the content of heavy metal cadmium in wheat and corn grain,and ensuring that the content of cadmium in grain is lower than the national limit.Therefore,considering the reduction of cadmium content in grains and the purpose of grain production,restoration schemes such as planting low cadmium accumulation wheat or spraying foliar conditioners or wheat jade rotation can be adopted.(2)Under the wheat chrysanthemum rotation mode,spraying leaf conditioner and applying passivation agent can reduce the cadmium content in wheat grains and marigold flowers,reaching the product safety standards.At the same time,marigold rhizome tissue can remove a small amount of effective cadmium in the soil through phytoremediation,so as to achieve the purpose of soil repair.Based on the planting of wheat,corn and marigold in the early stage,the income and cost profit rate per mu are calculated according to the market price sales and actual planting expenditure,and the economic benefits of the two models of wheat maize rotation and wheat marigold rotation are analyzed to find a planting model with high economic benefits.The results show that:(1)Both planting modes can generate profits,with a safe production mode of wheat and corn rotation earning 456.2 yuan per mu,and a safe production mode of wheat and marigold rotation earning 2732.2 yuan per mu.(2)The cost of passivation agents is high,and wheat+passivation agent treatment can lead to economic losses,so it is necessary to rotate with corn or marigold to increase profits;The profit from the safe production mode of wheat and marigold rotation is much higher than that of the wheat and corn rotation mode.Through integrated application and comprehensive analysis,low-cost needs can be considered,and repair solutions such as low cadmium accumulation wheat or spraying leaf surface conditioners can be adopted;Considering the demand for producing a large amount of grain and feeding poultry,a wheat jade rotation restoration plan can be adopted;Considering high economic benefits and the long-term goal of soil cadmium pollution remediation,a wheat chrysanthemum rotation remediation plan can be adopted. |
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