Biochar and engineered biochar as slow- and controlled-release fertilizers

Biochar, characterized by high specific surface area and porosity as well as by the presence of various functional groups, can be an excellent matrix for creating fertilizers that slowly release nutrients (slow-release fertilizers and controlled-release fertilizers). Co-composting, co-pyrolysis or co-application biochar with synthetic fertilizers allow for biomass utilization and provide resources for environmental protection. This review aimed to collect existing knowledge on possible applications of biochar in order to obtain controlled-release fertilizers. The methods for the production of biochar fertilizers have been described, and at the same time, attention is paid to potential risks associated with the use of this type of materials in the context of their toxic effects on plants and soil organisms.