The use of co-composted biochar (COMBI) made by the addition of biochar at the beginning of the composting process has greatly increased in agriculture during the last decade. There are more benefits of using the co-composting end product COMBI than using compost and biochar separately or the mixture of the two products. We conducted an extensive review of the production of several COMBIs and their contribution to the composting process and biochar properties as well as the further use of COMBIs in agricultural lands to improve soil health and increase crop yields, and to remediate areas severely contaminated with potentially toxic metals (PTMs). Although the number of researches focused on COMBI production and its application is so far limited, there is enough evidence to elucidate the importance of creating such products to promote sustainable agriculture and environmental safety. Even if a few drawbacks or side effects are found, they are outweighed by the many benefits achieved with COMBIs production and application in comparison to other amendments. The quality of both biochar and compost is largely improved in so many ways during the co-composting process, which in turn improved soil health and crop yields of up to 300% in some particular cases. This work improved the overall understanding of COMBI production and application in agriculture. Based on the review, we suggested future researches to better understand the mechanisms of COMBI long-term application to promote awareness on its role over time through alterations in its surface chemistry, ionic nutrient adsorption, supply (aging effect), and environmental implications.

Biochar produced from pyrolysis of biomass such as wood, canopy, animal manure, and agricultural waste is recognized for its stability and for being a benefactor of soil health and plant growth. Its application in forestry is an area with growing research interest due to its ability to enhance soil physicochemical properties, including structure, water retention, and nutrient availability, thereby boosting plant growth, drought tolerance, and resistance to pests and diseases. However, the effectiveness of biochar varies based on factors like biochar type, application rate, soil type, and tree species. Potential risks associated with biochar use include nutrient immobilization, increased pH in alkaline soils, and enhanced leaching of toxic elements. Despite its promise, challenges such as knowledge gaps, lack of site-specific studies, and concerns of economic viability hinder widespread adoption of biochar in forestry. This qualitative review compiles over 150 published works from the past two decades on biochar application in forestry. It assesses the impacts of biochar on soil health and tree crops, highlighting its potential to improve soil fertility and promote tree growth. The review identifies significant findings, such as the positive influence of biochar on soil and plant health and outlines existing knowledge gaps that need addressing. By synthesizing current research, the review proposes future directions to optimize biochar use in sustainable forestry management, emphasizing the need for tailored approaches and economic assessments to facilitate broader adoption. The findings underscore the potential role of biochar in enhancing forestry practices while calling for further studies to resolve uncertainties and improve its practical implementation. Graphical Abstract