FROM BULK TO NANO: BIOCHAR-BASED SEED COATINGS AND THE EMERGING POTENTIAL OF NANOBIOCHAR

Abstract

Growing demand for sustainable crop production has increased  interest in seed coating methods that enhances nutrient-use efficiency, support microbial growth, and promote early seedling establishment while reducing dependence on chemical inputs. Nanobiochar, produced by reducing the size of biochar particles and functionally modifying their surfaces, combines biochar’s porous structure and surface functionality with enhanced reactivity and loading capacity. Together, these characteristics makes nanobiochar as a potentially multifunctional material for seed coatings. This review critically evaluates nanobiochar-based seed coatings, with particular emphasis on feedstock- and pyrolysis-dependent properties, nanosynthesis and functionalization strategies, characterization techniques, coating technologies, and the mechanisms governing nutrient and microbial delivery. It also examines the potential of nanobiochar to enhance germination and seedling establishment, improves nutrient availability, reduces drought, salinity, and heavy-metal stress, and suppress soil-borne pathogens. Evidence derived directly from seed-coating studies is distinguished from mechanisms inferred from bulk-biochar applications and other nanoparticle-based seed treatments. In addition, the review considers the environmental and agronomic implications of nanobiochar, including its potential contributions to carbon management, reduction of agrochemical use, and economic feasibility. Particular attention is given to material variability, coating stability, nanoparticle aggregation, environmental fate, non-target effects, food-safety concerns, and the limited availability of field-scale and multi-season evidence. Overall, nanobiochar-based seed coatings represent a mechanistically promising but empirically emerging technology. Their agronomic, environmental, and economic benefits require systematic validation under standardized, field-relevant conditions.