Changes in Soil Properties, Content of Cd, and Cd-Resistant Bacterial Community with Biochar After One-Time Addition Under Soybean Continuous Cropping and Crop Rotation Patterns

In recent years, Cadmium (Cd) pollution in soybean farmland is severe. Therefore, this study focused on whether biochar influences soil physiochemical properties, the Cd content in soil and soybean grains, and the abundance and community structure of the czcA gene. Four doses of rice husk biochar (0, 5, 15, and 25 t·ha−1) were applied under continuous cropping and crop rotation systems, and soil samples were collected after four years of one-time addition. The results indicated that biochar addition significantly increased soil available nitrogen, phosphorus, and soil organic carbon contents under continuous cropping and rotation. Biochar application significantly reduced the total Cd content of soil samples and soybean grains. Additionally, biochar application reduced czcA gene abundance in soybean soils by 14.26–37.88% and 35.96–48.71%, respectively. Correlation analysis revealed that Cd content and the abundance of the czcA gene significantly correlated with soil nutrients and pH. High-throughput sequencing revealed that the relative abundances of several Cd-resistant microorganisms were decreased by biochar addition. In addition, adding biochar significantly affected the Cd-resistant microbial community structure and diversity by influencing soil properties and Cd content. Therefore, this study has important practical significance for improving the soil environment and ensuring the quality and safety of agricultural products.