| In calcareous soil,due to the high p H of the soil and it is difficult to passivate cadmium through lime effect,the remediation of cadmium pollution in calcareous soil in northern China has become a difficult point and a research hotspot.In this paper,for calcareous soils,the effects of different carbon sources such as biochar on cadmium in calcareous fluvo-aquicl soil and the absorption and transport of cadmium by crops are first explored through pot experiments.Furthermore,the release of organic acids in rhizosphere soil was simulated by culture experiment,and the release kinetic characteristics of cadmium and the changes of soil enzyme activities in calcareous aquic soil under the combined action of biochar and organic acid were explored.Finally,by equilibrium adsorption and adsorption kinetic(thermal)mechanics,the adsorption-desorption characteristics and long-term effects of cadmium in calcareous soil under the treatment of carbon of graduate matter were obtained.This study aims to reveal the remediation effect and mechanism of biochar on cadmium pollution in calcareous soil,and to provide a basis for rational use of biochar to remediate heavy metal cadmium pollution in calcareous soil and improve the safety of agricultural products.The main findings are as follows.1.Effects of different biomass carbon sources on growth and cadmium uptake of Chinese cabbage in polluted fluvo-aquicl soil.Through the pot experiment,the treatments of glucose,fulvic acid and maize biochar were set,and no carbon source was used as the control(CK).Compared with CK,the biomass of Chinese cabbage(fresh weight)decreased by 36.66%,the biomass of fulvic acid and maize biochar treatment increased by 3.6% and 47.3%,respectively.The cadmium content of Chinese cabbage leaves decreased by 43.5%,39.5% and 25.7%.Malondialdehyde content decreased by 23.6%,28.5% and 27.8%,respectively.The activities of Superoxide dismutase and Peroxidase in leaves were significantly enhanced,the content of non-protein thinning groups such as GSH and PCs was significantly increased,and the resistance of Chinese cabbage was enhanced.Compared with CK,the soil organic matter and available phosphorus content of maize biochar increased by 37.4% and 11.9%,respectively.The available cadmium content of glucose,fulvic acid and maize biochar decreased by 14.2%,9.3% and 14.1%,respectively,and the stability of cadmiumwas enhanced.The activities of soil catalase,urease and alkaline phosphatase were enhanced to promote nitrogen and phosphorus cycling.2.Effects of interaction between biochar and organic acids on the availability and enzyme activity of cadmium in contaminated fluvo-aquicl soil.Through the culture test,six common organic acids were secreted and set to apply and not apply biochar respectively.The results show that maize biochar reduced the activation effect of organic acids on cadmium.Compared with CK,the effective cadmium content of organic acid treatment increased significantly by 13.4%-19.4%,tartaric acid and malonic acid have the strongest ability to activate cadmium.Compared with organic acid treatment,maize biochar reduced the activation effect of organic acid on cadmium,and the maximum reduction rate was 5.3%.The activities of catalase,alkaline phosphatase,urease and dehydrogenase were enhanced by maize biochar and organic acid treatment.The content of available phosphorus in fluvo-aquicl soil treated with organic acid increased by 1.9%-73.2%,and the available phosphorus content increased by 79.9%-117.7% in the treatment of maize biochar and organic acid,which promoted soil nutrient cycling.3.Based on the long-term localization experiment in the field,the adsorption-desorption characteristics of cadmium in calcareous soil after long-term treatment of the graduate material charcoal.The results are as follows.(1)It was found that wheat and maize biochar still maintained cadmium fixation ability after many years of application to the soil.Compared with CK,the adsorption capacity of cadmium in wheat and maize biochar treatment in fluvo-aquicl soil increased by 7.4% and 9.4%,respectively.The adsorption capacity of cadmium in wheat biochar treatment in cinnamon soil increased by 6.7%.The p H of soil solutions with different adjustments also affected the amount of cadmium adsorption in soil,and the cadmium holding amount was significantly greater than that under slightly acidic conditions when the solution was alkaline.(2)It is found that the kinetic adsorption process of cadmium in fluvo-aquicl soil and cinnamon soil can be divided into fast reaction stage,medium reaction and slow reaction stage,the adsorption rate of cadmium in the fast reaction stage is fluvo-aquicl soil > cinnamon soil,biochar treatment > no biochar treatment.A variety of kinetic models were used to fit the kinetic adsorption data of cadmium in soil,and it was found that the fit of Elovich and pseudo-second-order kinetic model was the best.Different temperatures affected the negative free energy(△G)in the cadmium adsorption reaction in fluvoaquicl soil and cinnamon soil,indicating that cadmium adsorption was a spontaneous reaction,mainly chemical reaction,and increasing the temperature helped soil and biochar particles to adsorb cadmium.(3)In the isothermal desorption experiment,the desorption rate of cadmium in fluvoaquicl soil and clay increased with the increase of cadmium addition concentration.When the soil solution was acidic,the cadmium desorption rates of fluvo-aquicl soil and cinnamon soil were9.3%~38.3% and 7.9%~35.6%,respectively.When the soil solution is alkaline,the cadmium desorption rate of fluvo-aquicl soil and cinnamon soil were 2.5% ~ 27.8% and 1.6% ~ 19.2%.The data showed that the cadmium desorption rate of cinnamon soil was lower than that of fluvo-aquicl soil,and the desorption rate of cadmium in soil under acidic conditions was higher than that under alkaline conditions.In the adsorption kinetics test,when the soil solution was alkaline,the desorption rate of cadmium in fluvo-aquicl soil was reduced by 9.5% under the treatment of maize biochar,and the desorption rate of cadmium in cinnamon soil was reduced by 67.6% when the soil solution was treated with wheat biochar,the data showed that the desorption rate of soil cadmium was reduced by biochar in alkaline soil solution.In summary,the application of biochar in calcareous soil can reduce soil cadmium bioavailability,alleviate crop cadmium stress,reduce cadmium uptake of crops,increase soil available phosphorus and organic matter content,and promote the increase of Chinese cabbage biomass. |
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