Biochar from agricultural and forestry residues: research trends, technical evidence, and scale-up challenges

Biochar production from agricultural and forestry residues has expanded rapidly, but integration among research trends, production conditions, material properties, and large-scale implementation remains limited. This review combined bibliometric analysis with a critical synthesis of studies published between 2015 and 2025 and indexed in Scopus and Web of Science. After screening, 1,904 articles were included in the bibliometric analysis; 1,130 provided technical information on biochar production and properties, and 119 addressed implementation and scale-up. Scientific output increased 6.6-fold over the study period, accompanied by thematic diversification around thermochemical conversion, biochar properties, and environmental and agronomic applications. Agricultural and agro-industrial residues predominated, and pyrolysis was the most frequently reported conversion route. Under comparable within-study conditions, increasing temperature tended to reduce biochar yield and volatile matter while increasing fixed carbon and ash contents, and was also associated with carbon enrichment, lower H/C and O/C ratios, and higher pH and specific surface area. However, residence time, heating rate, atmosphere, reactor configuration, and operating mode were reported less frequently, limiting comparability among studies. Evidence related to implementation remained fragmented: 75.6% of the studies addressed only one analytical dimension, whereas 5.9% integrated three or more. This contrast highlights a gap between experimental knowledge of biochar production and properties and its translation into technically viable and scalable systems. Progress toward scale-up requires integrated assessments of process conditions, product characteristics, logistics, environmental performance, economic feasibility, standardization, and operational safety.