Title : Production and characterization of hemp fiber-derived biochar for agricultural applications
Abstract:
Industrial hemp (Cannabis sativa L.) is increasingly recognized as a multipurpose crop due to its high biomass productivity and its suitability for fiber, seed, and bio-based material production. However, hemp fiber processing generates considerable amounts of lignocellulosic residues, mainly hurds, whose sustainable valorization remains a relevant challenge within circular bioeconomy strategies. Among the available conversion pathways, pyrolysis represents a promising approach, allowing the production of biochar, a carbon-rich material with potential applications as soil amendment. This study investigates the production and characterization of biochar derived from hemp fiber processing residues, with the aim of evaluating its suitability for agricultural applications. Raw hemp hurds were directly converted through a fixed-bed pyrolysis process performed at 550 °C under nitrogen atmosphere, without preliminary grinding or pelletization. The resulting biochar was characterized through proximate and ultimate analysis, pH determination, elemental and metal content analysis, thermogravimetric analysis, scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, and phytotoxicity assessment through germination tests on corn (Zea mays L.) seeds. The pyrolysis process produced a solid fraction of approximately 40.3%, together with gaseous and liquid by-products. The hemp-derived biochar showed a high carbon content, above 75%, an alkaline pH of 9.63, and low H/C and O/C molar ratios, indicating a stable and highly carbonized material. The presence of relevant macro- and micronutrients, particularly potassium, calcium, magnesium, iron, manganese, zinc, and boron, suggests potential agronomic value. Moreover, heavy metal concentrations were below regulatory limits, supporting the environmental compatibility of the material. SEM-EDS analysis revealed a compact but porous structure, with micropores comparable to those observed in woody biomass-derived biochars, potentially favorable for nutrient retention, water holding capacity, and interaction with soil microorganisms. Germination tests showed that low biochar concentrations did not exert phytotoxic effects, with germination index values above 90% at 0.5–1% biochar concentration. Conversely, higher concentrations resulted in reduced germination performance, indicating the need to optimize application rates and further evaluate possible pre-treatments. Overall, the results highlight the potential of hemp fiber-derived biochar as a sustainable soil amendment and demonstrate the feasibility of directly valorizing hemp processing residues through thermochemical conversion. These findings provide a useful basis for future agronomic trials focused on soil fertility, water retention, and crop response.
