Effects Of Biogas Fertilizer/Passivator On Heavy Metal Cd/Cr In Soil And Spinach

Soil heavy metal pollution has threatened human health and life safety,and the harm of heavy metals is closely related to its occurrence form.As an important organic fertilizer,how to apply biogas fertilizer scientifically is very important to improve the quality and yield of agricultural products and reduce heavy metal pollution.The effects of biogas fertilizer and different kinds of passivators（zeolite,red mud,calcium magnesium phosphate fertilizer）on soil heavy metals Cd and Cr were studied by pot experiment.The BCR continuous extraction method was used to analyze the forms of heavy metals,and the changes of the content and distribution rate of heavy metals,the passivation effect and the soil pollution index were analyzed.The bioaccumulation coefficient was calculated by detecting the heavy metal contents in roots,stems and leaves of spinach,and the correlation between the contents of exchangeable and available forms in soil and the contents of heavy metals in spinach were analyzed In order to reduce the bioavailability of Cd and Cr in soil,the interaction between humus and heavy metal speciation in soil was analyzed by the extraction method of KCl、Na₄P₂O₇、Na OH、HNO₃.Fourier transform infrared spectroscopy and two-dimensional correlation spectrum were used to analyze the spectral characteristics of soil before and after the experiment.The binding mechanism of heavy metals Cd,Cr and organic matter in soil was clarified The reasonable utilization of the liquid and the treatment of soil heavy metal pollution provide certain scientific data.The main conclusions are as follows:（1）When biogas fertilizer or biogas fertilizer+passivator was applied to the soil,the exchangeable contents and distribution rates of Cd and Cr decreased,while the residual contents and their distribution rates increased,The results of variance analysis showed that the contents and distribution rates of exchangeable and residual forms of Cd and Cr,as well as the passivation effects of exchangeable and available forms of Cd and Cr were significantly affected by biogas fertilizer or biogas fertilizer+passivator（P<0.05）.（2）Applying biogas fertilizer or biogas fertilizer+passivator,the contents of Cd,Cr and bioconcentration coefficient in spinach and its stems and leaves decreased,and the order of Cd,Cr content and bioconcentration coefficient in roots,stems and leaves was root>stem>leaf.The results of variance analysis showed that the application of biogas fertilizer or biogas fertilizer+passivator had significant effects on Cd,Cr content and bioconcentration coefficient of spinach and its stems and leaves There was a significant positive linear correlation between the contents of Cd and Cr in spinach and the contents of available and exchangeable Cd and Cr in soil.（3）When biogas fertilizer or biogas fertilizer+passivator was applied,the main heavy metal Cd in soil was organic complex and organic bound,Cr was mainly in residual form,followed by organic bound and organic complex.The proportion of water-soluble and exchangeable Cd and Cr in soil decreased after the test,while the proportion of residual Cd and Cr increased.The results of variance analysis showed that the application of biogas fertilizer or biogas fertilizer+passivator had significant effects on the water-soluble,exchangeable and residual forms of Cd and Cr,and the proportion of HA-Cd and HA-Cr in the soil was significantly affected by biogas fertilizer or biogas fertilizer+passivator（P<0.05）.（4）Fourier transform infrared spectroscopy（FTIR）and two-dimensional correlation infrared spectroscopy（2D-IR）were used to analyze the spectral characteristics of soil before and after planting.The contents of amide compounds,carbohydrates,proteins,sugars and other organic matter decreased,while the contents of aromatic humus increased.The results of absorption peak intensity analysis showed that the application of biogas fertilizer and calcium magnesium phosphate fertilizer had the highest degree of soil humification.In the range of 1800cm^-1～900cm^-1,the two-dimensional correlation infrared spectra showed that there were synergistic effects in the process of protein,aromatic ring and polysaccharide in soil,but different treatments showed different synergistic effects.Biogas fertilizer or biogas fertilizer+passivator could enhance the degree of soil humification,and the effect of biogas fertilizer+calcium magnesium phosphate fertilizer was more obvious.