Valorization of agro-industrial and forestry biomass ashes as soil amendments: integrating chemical screening, leaching dynamics, and Beta vulgaris L. response

Abstract Sustainable management of biomass combustion ash is critical for circular economy transitions. This study provides a comprehensive evaluation of six biomass ashes (wood chips, forest residues, maize cobs, plum pits, sugar beet pulp, and distillery decoction) as potential soil amendments. Chemical characterization and leaching tests revealed high concentrations of Ca, K, Mg, and P, confirming significant agronomic potential. However, ashes from beet pulp and distillery decoction exceeded EU arsenic limits by up to 5.5-fold, with distillery decoction ash releasing 69% of its As during leaching. A pot experiment with Beta vulgaris L. demonstrated that ash application at 2–8 Mg ha⁻¹ consistently increased soil pH and enhanced fresh biomass by up to 59%, particularly when combining nutrient-rich and Ca-rich ashes. Nevertheless, high application rates of specific blended variants increased Pb and Cd uptake in roots, likely driven by dissolved organic carbon (DOC) mobilization. These findings indicate that while biomass ashes effectively correct soil acidity and improve crop yields, their valorization requires rigorous feedstock screening and dose control to ensure regulatory compliance and food safety.