Study on the Effect of Modified Biochar on the Available State of Heavy Metals in Soil

Heavy metal pollution in agricultural soil is a global issue that seriously threatens agricultural production and human health. Biochar has attracted significant attention as an efficient and environmentally friendly material for remediating heavy metal pollution in soil. In this study, biochar (BC) was prepared from tobacco straw and then modified with polyethyleneimine (PEI) using a mixed co-impregnation method to create polyethyleneimine-modified biochar (PBC). The structure and surface properties of BC and PBC were analyzed, and their effects on the physiological characteristics of Chinese cabbage, as well as the accumulation of cadmium and copper in Cd and Cu-contaminated soil, were studied. The results indicated an increase in the pore volume and pore size of the modified BC, with successful impregnation of PEI on the BC surface. The introduction of functional groups, such as amine groups, enhanced the adsorption of biochar. After 70 days of cultivating young plants, the growth status of Chinese cabbage and the soil’s physical and chemical properties were determined. Compared with the control ( CK), when the addition amount of PBC was 3%, the data were analyzed by one-way ANOVA. The indicators with significant changes were as follows: the content of available Cd and Cu in soil decreased by 54.68% and 43.76%, respectively. The plant height and root length of Chinese cabbage increased by 3.1 cm and 3.5 cm, respectively. The fresh and dry weights of leaves increased by 138.07% and 98.3%, respectively. The fresh and dry weights of the roots increased by 107.3% and 140.5%, respectively. The chlorophyll content of the leaves increased by 57.68%. The absorption and accumulation of Cd in roots and leaves decreased by 48.80% and 55.88%, respectively. The absorption and enrichment of Cu in roots and leaves decreased by 33.04% and 43.41%, respectively. The enrichment coefficients of Cd and Cu in Chinese cabbage leaves decreased by 47.45% and 40.92%, respectively, and in roots by 48.80% and 33.04%. In summary, PBC serves as an effective soil heavy metal stabilizer, significantly enhancing the physiological and biochemical indexes of crops in contaminated soil and reducing heavy metal accumulation in crops. This provides a scientific basis and technical support for researching and developing efficient soil heavy metal stabilization materials.