Granulation of wood ash for sustainable soil management: A multidisciplinary assessment of nutrient release and environmental safety

Sustainable soil management requires innovative technologies capable of closing nutrient cycles while ensuring environmental and human safety. Wood ash, a biomass-derived residue, is a valuable source of essential plant nutrients, yet its direct application is limited by poor handling properties, dust emissions, and potential environmental and health concerns. This study proposes granulation as an enabling environmental technology to convert raw wood ash into a safe and effective soil amendment suitable for practical deployment. Using a multidisciplinary approach, the granulated product was characterized for its chemical stability, nutrient release kinetics, and biological safety profile. The results demonstrate that the granules exhibited high potassium bioavailability, enabling rapid nutrient supply, while calcium and phosphorus were released more gradually from less soluble mineral phases, supporting sustained soil enrichment. The granulation process promotes carbonate formation, which provides an effective pH-buffering capacity (Neutralizing Value ∼32%) specifically suited for acidic soils. Environmental assessments confirmed that potentially hazardous elements remain well below regulatory limits, ensuring low leaching risk. Biological assays demonstrated selective antibacterial activity against Gram-negative bacteria and biocompatibility at application-relevant doses supporting safe handling during field application. Overall, this study demonstrates that granulated wood ash functions as a technology-enabled soil amendment that enhances nutrient recycling and reduces environmental and health risks, providing fundamental environmental evidence to support its uptake within circular economy-based soil management strategies.