Evaluation of ash derived from conversion of contaminated Miscanthus × giganteus biomass as a soil amendment: impacts on soil parameters and physiological characteristics of Zea mays L.

Biomass ash (BA) is a sustainable soil amendment with the potential to reduce dependency on chemical fertilizers, enhance soil quality, and improve crop productivity, in accordance with the principles of the circular economy. This study evaluated the effects of Miscanthus × giganteus ( M×g ) ash, derived from biomass grown on trace element (TE) contaminated land in France, applied at rates ranging from 0 % to 7 %, on soil properties, nutrient dynamics, and the physiological responses of the test plant, Zea mays L. The study results demonstrated that BA application significantly increased soil pH (from 6.2 to 7.5) and electrical conductivity (from 0.42 to 2.14 dS m −1 ), indicating enhanced buffering capacity and ion-exchange potential. The soil organic carbon content reached a maximum of 3.8 % with a 5 % ash application rate, suggesting its potential for carbon sequestration. Nutrient analysis revealed a substantial increase in K concentration, reaching 51,691 mg kg −1 in the plant leaves at the 7 % BA level, while Mg and P concentrations decreased to 826 and 567 mg kg −1 , respectively, at the same dose. A higher ash application rate (7 %) caused physiological stress and nutrient imbalances, thereby limiting the growth of Z. mays plants. These findings highlight the dual effects of BA as a soil amendment: while lower application rates (1 % and 3 %) improve soil fertility and plant growth, higher doses (5 % and 7 %) pose potential risks. Given the large-scale availability of M×g BA from the thermal conversion of biomass cultivated on TE-phytoremediated sites, these results support its practical use in sustainable agriculture and land reclamation, provided that application rates are carefully optimized to balance benefits and risks.