Biochar, known as “Black Gold”, has become a novel approach with potential benefits for soil amendment, such as improving soil physicochemical properties, reducing greenhouse gas emissions, and enhancing soil fertility. The previous research studies mainly focus on exploring different methods for the improvement of biochar enriched nutrients as fertilizers; however, the migration and transformation mechanisms of these nutrients induced by biochar are yet to be extensively investigated. This paper provides an overview of recent advances in the application and mechanisms of biochar for soil amendment focusing on soil properties and nutrients improvement. Biochar positively alters microbial-mediated reactions in the soil C and N cycles, i.e., mineralization of C and N, and N₂ fixation, thus enhancing maximizing C and N use efficiency and reducing the potential losses. Moreover, biochar provides reactive surfaces where P and K ions are retained in soil microbial biomass and in exchange sites, leading to increasing the availability of P and K to plants uptake. In addition, the toxic substances and potential ecological risks of biochar were also reviewed and discussed, thereby providing a baseline reference and guiding significance for future biochar applications as promising soil amendments.

Biochar, as an emerging biotechnology, has been widely used in the remediation of soil organic pollution, mainly by promoting the abundance of related degrading bacteria in soil. In this study, we explored the influence of sewage sludge biochars pyrolyzed at different temperatures of 300–700 °C (SSB₃₀₀-SSB₇₀₀) and addition rates (1% and 5%) on the atrazine biodegradation in soils. After a 21-day incubation, the application of 5% SSB₃₀₀ significantly increased soil catalase (CAT), urease activity, dissolved organic carbon (DOC), and electrical conductivity (EC). However, biochar amendment exhibited inhibitory effects on atrazine degradation in soils. The atrazine degradation ratio decreased with decreasing pyrolysis temperature and increasing addition rates. Further analysis found that there were two possible reasons for the significant decline of atrazine biodegradation in SSB₃₀₀ groups: (1) SSB₃₀₀ demonstrated higher adsorption capacity for atrazine compared to SSB₅₀₀ and SSB₇₀₀ and reduced atrazine bioavailability due to its stronger hydrophobic nature and more abundant surface functional groups; and (2) the SSB₃₀₀ significantly decreased the abundances of dominant atrazine-degraders (Arthrobacter and Pseudomonas) and atrazine-degrading genes (atzA, atzB, and trzN).