Review of selecting suitable biochar for biochar-based fertilizer application in sustainable agriculture

Global agriculture faces the critical challenge of feeding nearly 10 billion people by 2050, while minimizing environmental harm and preserving the socioeconomic stability of the world. Biochar, a carbon-rich material with unique physicochemical properties like surface area and pore space, has been proven to be go for soil amendment by improving nutrient retention, water-holding capacity, and microbial activity while mitigating greenhouse gas emissions. However, its inherent nutrient deficiency limits its use as a standalone fertilizer. Integrating biochar with nutrient-rich organic and inorganic materials to produce biochar-based fertilizers (BBFs) offers a promising path toward sustainable crop production. Evidence from recent studies indicates that BBFs can increase crop yield by up to 94%, reduce nitrate leaching by 68%, and enhance soil phosphorus availability by 45%, supporting soil health and nutrient efficiency. However, BBFs performance depends strongly on biochar type used, enrichment materials, production methods, and soil conditions. Despite these benefits, high production costs, scalability constraints, and a lack of standardization hinder widespread adoption. Beyond these facts, this review identified trends in the types of biochar used for BBF production and a gap in studies that critically evaluate biochar choice in the overall performance of BBFs for sustainable crop production, considering agronomic, environmental, and economic indices. The analysis highlights critical gaps, including inconsistent yield responses in fertile soils and the uncertain long-term behavior of heavy metals in manure-derived biochar. To address these, we propose that future studies should focus on direct performance comparisons of different biochars when utilized for BBF production, a framework for standardized evaluation of biochar feedstocks, regional field validation, and life-cycle economic assessment to accelerate BBFs adoption as a nutrient-efficient, climate-resilient alternative to conventional fertilizers.