Circular utilization of Miscanthus×giganteus biomass ash to enhance soil quality and support its regrowth

Abstract The increasing production of biomass ash (BA) from the thermal treatment of energy crop residues necessitates sustainable strategies to reduce environmental burdens while enhancing soil fertility. Despite its potential value, significant amounts of BA are still disposed of in landfills or remain underutilized, indicating a lost opportunity for resource recovery. This study explores a circular economy approach for the valorization of Miscanthus × giganteus ( M × g ) BA, originating from the energy conversion of M × g biomass produced on trace element-contaminated soil, through its reintegration into the next M × g plantation cycle. Under controlled conditions, BA was applied at 1%, 3%, and 7% (mass fraction) to the soil during M × g plantation to evaluate changes in soil properties, nutrient dynamics, and plant physiological responses. BA incorporation significantly increased soil pH and electrical conductivity in line with increasing doses, while total organic carbon rose from 0.81 to 0.96 mg/kg (7% BA with M × g ). However, carbon mineralization declined by 64% at the highest dose of BA. Nutrient availability was notably altered: phosphorus increased from 77 to 2167 mg/kg, and potassium increased from 6 to 460 mg/kg, while calcium decreased by 73% at 7% BA. M × g biomass production improved at 1% BA but declined at higher doses, indicating a dose-dependent physiological response. Chlorophyll content decreased with increasing BA doses, while carotenoids increased, suggesting a stress adaptation mechanism. Antioxidant activity diminished, indicating oxidative stress. Elemental uptake patterns shifted across BA levels, with stems accumulating more K and Ni and less Mg, Ca, and Mn. Silicon peaked at low doses of BA but declined at higher values; phosphorus followed a non-linear trend between tissues. The findings highlight the potential of M × g BA as a soil amendment and demonstrate a regenerative circular system that transforms a waste by-product into a valuable resource for supporting plant growth and soil quality. Optimizing application rates is essential to balance benefits with potential stress effects. Graphical abstract