Effects Of Different Cow Dung Treatments On Cadmium Occurrence Forms In Contaminated Yellow Soi

Cattle farming produces a large amount of manure,and new ways of resource utilization of cow manure in Guizhou need to be explored.However,the content of cadmium in the soil seriously restricts the grain production of"strictly controlled"cultivated land.Whether it can be returned to the field through cow dung-based fertilizer to inhibit the bioavailability of cadmium,so as to propose a new way of green production of agricultural resources,which needs to be further developed research.Therefore,in this study,the products obtained from three kinds of cow manure treatment methods(fresh cow manure,aerobic composting,and anaerobic fermentation)were used as the test materials to explore the morphological characteristics of cadmium in soil after the products were returned to the field,and further explore the cadmium-rich products.The key microbial genus that collected or sensitive characteristics were compared,and the optimal treatment methods and application rates of cow dung were obtained.The main conclusions are as follows:(1)The three treatments had different effects on the cadmium species in the two types of soilsIn the safe-utilization soil,returning fresh cow manure to the field promotes the conversion of exchangeable cadmium to the other three forms of cadmium;returning compost to the field promotes the conversion of exchangeable cadmium and residual cadmium to reducible and oxidizable cadmium;biogas fertilizer Returning promotes the conversion of exchangeable and oxidizable cadmium to reducible and residual cadmium.All three treatments of cow dung can promote the transformation of exchangeable cadmium,reducible cadmium,and oxidizable cadmium to residual cadmium in strictly controlled soil.(2)Soil pH is a key factor regulating the speciation characteristics of cadmium in soil after returning to the fieldThe results showed that pH had a stronger influence on soil Cd morphology than organic matter,and there was an extremely significant negative correlation between pH and exchangeable Cd(R~2=0.516)reducible Cd(R~2=0.528)oxidized Cd(R~2=0.744).The increase of pH promoted the transformation of Cd to stable form.(3)The method of returning biogas fertilizer to the field is the best in the safety and control soil,and 500,1500-2000kg/mu is the most suitableThe passivation rate of cadmium by the cow dung biogas fertilizer returning to the field is remarkable,which is 34.40-52.87%24 hours after returning to the field;The passivation effect lasts for more than 120 days;The effect on strictly controlled soil is obviously better than that of safe use soil;When the application rate of 1500-2000kg/mu was treated in the strictly controlled soil,the effect of reducing soil cadmium bioavailability and mobility was the best.In addition,the optimum application rate for safe use of soil is 500kg/mu.(4)Discovery of cadmium-responsive functional bacteria in biofertilizationBBMC-4 and Turicibacter were significantly negatively correlated with oxidizable cadmium(R~2=0.7853),and residual cadmium was extremely significantly positively correlated with R~2 of 0.8128 and 0.9245,respectively,implying the discovery of key functional cadmium emergency bacteria,they specifically expanded or decreased under cadmium stress,indicating their adaptability or sensitivity to cadmium stress.To sum up,the method of returning cow dung and biogas fertilizer to the field has the best passivation effect on cadmium in the soil,and has the advantages of quick effect and persistence.At 2000kg/mu(strictly controlled cultivated land),it can achieve an effective resistance and control effect,which has guiding significance for the production and application of green base fertilizer for karst cultivated land in Guizhou.