Effects Of Spent Mushroom Substrate Biochar On Cadmium Contaminated Soil Properties And The Yield And Quality Of Cabbage

Cadmium is a heavy metal that is very toxic to the human body.According to China’s official data,cadmium pollution is in a high proportion of inorganic pollutants.At the same time,biochar has been widely used in the adsorption of heavy metals,soil improvement and the increase of the crop production due to its special physicochemical characteristics,including a large specific surface area,an abundance of pores and surface functional groups,and a high surface negative charge and charge density.With the rapid development of edible fungus industry,it is urgent to provide a new way for the utilization of spent mushroom substrate.Thus,spent mushroom substrate was used to make biochar to research the adsorption of Cd in aqueous solutions under the effects of different factors.On this basis,a pot experiment were designed to research the effects of spent mushroom substrate derived biochar on physicochemical characteristics of cadmium contaminated soil,soil enzyme activity,changes of soil heavy metal speciation and so on,analyzing the relationship between physicochemical properties of the soil,soil enzyme activity and soil exchangeable heavy metal content.At the same time,we study the effects of spent mushroom substrate biochars on the yield and quality of cabbage,and these results are as follows:（1）With the increase of pyrolysis temperature,the yield,value of CEC of biochar decreased,while the ash content,pH value,specific surface area and surface functional group increased.The adsorption of Cd²⁺on the spent mushroom substrate biochar can be better fitted by the pseudo-second-order kinetic model and Langmuir model,which indicates that the adsorption of Cd²⁺on the spent mushroom substrate biochar is mainly chemical adsorption and monolayer adsorption.At the same time,the maximum adsorption capacity of PC、SC for Cd²⁺was 71.49 and46.87mg/g,respectively.（2）Biochar application can increase soil water content,pH,the content of organic matter and available nutrients,while the value of CEC decreased.When compared with the control,the content of soil organic matter increased 61.2%（PC-C）and 80.6%（SC-C）,the content of soil available phosphorus increased to 104.88%（PC-C）and 59.02%（SC-C）,and the content of soil available potassium increased to 486.8%（PC-C）,503.09%（SC-C）.The content of soil alkali hydrolysable nitrogen has the best effect on the amount of biochar added to 0.5%.（3）The activity of catalase,urease and sucrase in soil could be significantly increased by the biochar application.The soil catalase increased by 22.37%when the amount of PC was 1%,and the soil catalase increased by 18.39%when the amount of SC was 2%.And the content of soil sucrase increased to 33.28%（PC-C）,29.81%（SC-C）,respectively.（4）Biochar application can significantly reduce the exchangeable Cd content that can be absorbed and utilized by plants,increase the content of residual Cd,and the migration of cadmium in soil reduced.At the same time,the result of correlation showed that soil pH value,organic matter content and exchangeable cadmium content in soil had a negative correlation,the correlation coefficient are-0.709,-0.706,respectively.The content of cadmium in cabbage could be reduced effectively by the addition of biochar to soil.The cadmium content could be significantly reduced by 57.5%（SC）and 54.1%（PC）when the application amount is 2%.And the cadmium content in cabbage is significantly positively correlated with the exchangeable cadmium content in the soil,and the correlation coefficient is 0.759.（5）When the application amount is 0.5%,the yield of cabbage can be increased by 37%（PC）and 45%（SC）,and the chlorophyll content have similar result.The length,weight of root and leaf area of cabbage all increased with the increase of application amount of spent mushroom substrate biochars,and the optimal performance appeared when the application amount is 2%.The content of soluble sugar and vitamin C of cabbage showed the optimal performance when the application amount of spent mushroom substrate biochars is 1%,but the nitrate nitrogen content increased with the increase of the increase of application amount of spent mushroom substrate biochars,but it is lower than the national safety standard（3000 mg/kg）.（6）Grey relational analysis for evaluating the effects of different rates of spent mushroom substrate biochar application on a plant-soil system with cadmium contamination,and compared with the control,the application of biochar can effectively optimize the soil plant system.And the optimal performance appeared when the application amount is 2%.In conclusion,spent mushroom substrate biochars can effectively remove cadmium from water.Suitable spent mushroom substrate biochars application to cadmium contaminated soil can effectively improve soil physico-chemical characteristics,increase the activity of soil enzymes,improve the transformation of exchangeable soil cadmium to residual speciation,and reduce the content of cadmium in cabbage.The cadmium content in cabbage can reach the national food safety standards（GB 2762-2012）when the application amount is 2%.