Advancing Circular Bioeconomy Through Waste Valorisation: Synergistic Roles of Microbial Biofertilizers and Biochar in Climate-smart Agriculture

Despite extensive research on microbial biofertilizers and biochar as individual soil amendments, a critical knowledge gap remains regarding their integrated production from organic waste streams and their synergistic contribution to climate-smart agriculture. This review aims to consolidate current advances in waste valorization pathways that convert agricultural, municipal, and industrial residues into microbial inoculants and biochar, and to elucidate the biochemical and soil-plant mechanisms underpinning their combined functionality. Evidence across studies indicates that waste-derived microbial biofertilizers enhance soil nutrient dynamics through biological nitrogen fixation, phosphorus solubilization, siderophore-mediated micronutrient acquisition, phytohormone synthesis, and pathogen suppression, with liquid formulations offering superior microbial stability and activity. Concurrently, thermochemically produced biochar provides recalcitrant carbon for long-term sequestration, improves soil physicochemical properties, enhances cation exchange capacity, and serves as a protective microhabitat that sustains beneficial microbial communities. Their co-application consistently results in higher nutrient-use efficiency, soil enzymatic activity, plant biomass, and resilience to abiotic and biotic stressors compared to single amendments. Persistent constraints-including variable field performance, limited microbial survivability, quality inconsistencies, economic barriers, and inadequate extension support-limit widespread deployment. Emerging innovations such as omics-guided strain optimization, engineered microbial consortia, biochar functionalization, and regulatory frameworks provide promising avenues for overcoming these limitations. Overall, integrating microbial biofertilizers and biochar within circular bioeconomy strategies offers a robust, scalable pathway for enhancing soil health, reducing chemical fertilizer dependency, and advancing climate-adaptive agricultural systems.