The increase in the world population exerts significant pressure on expanding global agricultural production. To achieve this, the use of fertilizers is fundamental. However, highly soluble traditional chemical fertilizers can be easily leached and volatilized, causing environmental damage. Therefore, reducing the use of these fertilizers and developing new and smart fertilizers is crucial. Biochar, a solid and carbon-rich pyrolysis product, has been studied both as a standalone fertilizer and as a raw material for sustainable fertilizers. Recently, a wide variety of materials and techniques have been used in the production of biochar-based fertilizers (BBFs) and need to be grouped and critically evaluated. Thus, this study aimed to conduct a literature review on new biochar-based fertilizers, involving different routes for biochar-based fertilizer synthesis and their effects on various crops. Recent results indicate the growing interest in nanomaterials and microbial processes for producing new fertilizers. Most assessed studies use biochar to produce slow-release fertilizers. The results also indicate that these new biochar-based fertilizers increase crop yields and reduce the leaching and volatilization of nutrients in soil, demonstrating significant potential as an alternative to traditional fertilizers. Therefore, the agricultural use of biochar holds environmental importance by reducing the negative impacts caused by the use of highly soluble traditional fertilizers. However, long-term field experiments and the economic feasibility of BBF production routes must be carefully studied.

Biochar-based fertilizers (BBFs), including formulations enriched with additives, are sustainable alternatives to conventional fertilizers, promoting waste reuse and controlled nutrient release. This study performed a global meta-analysis to evaluate nutrient dynamics (release and leaching in water and soil) and the agronomic performance of additive-enhanced BBFs compared with unfertilized and/or conventionally fertilized controls. Thirty studies were selected, with 264 experimental pairs extracted from the Web of Science and Scopus databases, and analyzed using a random-effects model. The results indicated that BBFs enriched with natural mineral additives promoted an average increase of 204.3% in nutrient release in water (p < 0.001), whereas in soil biotechnological additives showed the greatest increase, with 109.8% (p < 0.001). Leaching was reduced by up to 74.4% with BBFs enhanced with agricultural residue additives and by 46.9% with industrial additives, indicating greater nutrient retention and greater nutrient-use efficiency. In terms of agronomic performance, additive-enhanced BBFs resulted in average increases of 49.3% in plant height, 232.3% in aboveground biomass, 60.8% in root biomass, and 11.2% in grain yield, compared to unfertilized soil. Overall, the effectiveness of BBFs depends on both the type of additive and the application method, with industrial and mineral additives being the most promising for controlled nutrient release and increased crop productivity.