Study On The Effect Of Three Kinds Of Straw Remediation Materials On The Remediation Of Light And Moderate Cd Contaminated Soil In Farmland

The remediation of light to moderate Cd-contaminated farmland soil and the disposal of straw waste off-site is currently a long-standing and difficult problem in China’s agricultural development.The perfect combination of the utilization of straw resources and the ecological remediation of farmland soil with light and moderate Cd pollution is becoming an important research direction for the development of green agriculture in China.In this study,common vegetables were selected as the test crops.Based on pot experiment and field experiment in greenhouses,we investigated the remediation effects and influencing factors of three remediation materials:organic fertilizer with straw digest,biochar with straw and crushed straw on acidulous and alkalescent Cd-contaminated farmland soils.Combined with material electron microscope characterization and adsorption experiments,the remediation mechanism of three straw-based remediation materials on Cd contaminated soil was discussed,and a feasible pathway for ecological remediation of light to moderate Cd contaminated farmland soil was proposed.The main research conclusions are as follows:（1）The results of potting experiments on remediation of weakly acidic and moderately Cd contaminated soil showed that the Cd content in leafy agricultural products did not exceed the standard after straw materials were combined with lime.Soil organic matter content and p H value increased significantly（P<0.05）,15 t·ha^-1 applied amount of straw and biogas residue organic fertilizer and 20 t·ha^-1 applied amount of straw biochar significantly reduced（P<0.05）the available state in the soil Cd content.The soil available Cd content has a very significant positive correlation with the leaf vegetable Cd content（P<0.01）,and a significant negative correlation with the soil organic matter content and p H value（P<0.05）.From the perspective of economics and agricultural product safety,7.5 t·ha^-1 applied amount of straw and biogas residue organic fertilizer combined with lime and weakly acidic moderately Cd contaminated soil is a suitable remediation method.（2）The potted experiment results of remediation of weakly acidic mildly Cd contaminated soil showed that three kinds of straw remediation materials can increase crop biomass and significantly reduce（P<0.05）crop enrichment coefficient and available Cd content in the soil.When the Cd content of the soil is≤0.5 mg·kg^-1,crushed straw is a suitable restoration material.When the Cd content of the soil is 0.5-0.7 mg·kg^-1,for leafy vegetables,the organic fertilizer of straw and biogas residue is Suitable repair materials.For nightshade vegetables,crushed straw is a suitable repair material.（3）The experimental remediation study of weakly alkaline mildly Cd contaminated soil in greenhouses showed that the three kinds of straw remediation materials can significantly（P<0.05）increase the biomass and soil fertility of leafy agricultural products,but have an effect on the content of soil available Cd and leafy vegetables.The effect of Cd enrichment in agricultural products is not significant.Pearson correlation analysis showed that soil bulk density was extremely negatively correlated with leaf vegetable biomass（P<0.01）.In weakly alkaline Cd contaminated soil,straw materials have little effect on the total amount of Cd and available Cd,but they can improve the soil aggregate structure,soil fertility and organic matter and increase the yield of agricultural products.From the perspective of agricultural product safety risk control,the organic fertilizer of straw and biogas residue is a suitable material for remediation of weakly alkaline Cd contaminated soil,and the suitable application amount is 7.5t·ha^-1.（4）Combining the electron microscope scanning and Cd adsorption experiments of three straw materials,the results show that the three straw repair materials have a large number of pores and have good adsorption;the adsorption capacity of the three straw repair materials for Cd is:straw biochar>Straw and biogas residue organic fertilizer>Straw.Redundancy analysis results show that soil available Cd and p H are the main factors for crops to absorb and accumulate Cd and affect the food safety of agricultural products.For farmland soils with mild to moderate Cd pollution,p H should be adjusted first to control the effective Cd content of the soil below 0.3mg·kg^-1,and then green remediation agents should be used to further stabilize the passivated soil Cd,and improve the soil aggregate structure and Soil fertility can achieve the effect of safe utilization of mild to moderate Cd polluted soil.