Response of Miscanthus × giganteus J.M. Greef et Deuter establishment and first-year biomass production to alternative soil amendments

Low risky establishment of Miscanthus × giganteus requires optimal management strategies that ensure stable nutrient availability and fast, uniform early growth. This study evaluated the effects of different amendments—organic materials, biomass combustion ash, and urea—on seasonal soil chemical dynamics and first‑year biomass production in an outdoor pot experiment. Seasonal monitoring revealed pronounced shifts in nitrogen availability, with high early‑spring values, a decline toward late summer, and partial recovery in autumn. Whereas total carbon decreased until mid‑May, increased through late summer, and declined again in autumn. The highest average nitrogen mineralization rate occurred in mid‑spring, followed by a gradual decrease, while immobilization prevailed toward the end of the season. A concurrent reduction in the C:N ratio was also observed. No significant differences among amendments were detected in CO₂ emissions, whereas soil moisture was lowest in the control and highest in the biomass ash treatment. Initial rhizome traits did not significantly affect biomass production, which was most strongly associated with shoot number and maximum plant height. The highest biomass yield was obtained with cattle manure, and the lowest with biomass combustion ash application. Variance partitioning confirmed the substantial role of amendments in early biomass production, with rhizome traits contributing only marginally. Amendments also markedly altered biomass allocation: willow compost and farm‑residue compost increased the shoot proportion, whereas mineral amendments enhanced the share of rhizomes and roots