Advances in Biochar-Based Slow-Release Fertilizers: Production Techniques and Their Applications

The practical application of biochar-based slow-release fertilizers (BSRFs) in sustainable agriculture has been steadily increasing due to their considerable potential to enhance crop yields, promote soil health, and alleviate negative environmental impacts. This review paper explored the methods used to produce BSRFs, including nutrient retention and release mechanisms. It aimed to integrate fragmented research, identify the optimal preparation approaches, and bridge the gap between laboratory findings and field applications. This study provided practical guidance for sustainable agricultural development by outlining key production methods that could enhance the use efficiency of BSRFs, including in situ pyrolysis, copyrolysis, impregnation, encapsulation, and granulation. A critical analysis of the published approaches suggested that an integrated production method was the most effective to provide high-performance BSRFs. The application of BSRFs was found to effectively improve the soil’ physical, chemical, and microbiological properties, while also enhancing the fertilizer consumption rate by up to 45%. The application of BSRFs improved crop growth and productivity, with increases ranging from 26% to 67%. From a mechanistic perspective, BSRFs reduced nutrient losses, particularly nitrogen leaching, by up to 71%, while enabling a controlled release profile that aligned with the dynamic nutritional demands of growing plants. Therefore, BSRFs are a viable strategy for minimizing agricultural pollution and supporting environmentally friendly crop production. Despite these benefits, there are still no standardized protocols for large-scale BSRFs manufacturing. Furthermore, long-term field trials are urgently required in order to evaluate the agronomic effectiveness, environmental safety, and overall sustainability of BSRFs in a variety of different agroecological conditions.