The roles of co-composted biochar (COMBI) in improving soil quality, crop productivity, and toxic metal amelioration

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. [Display omitted] •Production of co-composted biochar (COMBI) is an effective waste management method.•Composting with biochar improves physicochemical/biological properties of product.•COMBI better performs in soil than biochar, compost, or their simple combination.•COMBI improves soil health, crop productivity and reduces potentially toxic metals.