Integrated Fertilization Enhances Biomass Yield of Miscanthus × giganteus on Acidic Marginal Soils

Optimizing nutrient management is essential for improving the productivity and profitability of perennial bioenergy crops on marginal soils. This study evaluated the effects of mineral fertilization, a humic-based biostimulant, and a titanium-containing micronutrient preparation on the growth, biomass yield, and economic performance of Miscanthus × giganteus grown on acidic low-fertility soil in Western Ukraine from 2022 to 2025. A repeated-measures mixed-model analysis showed significant effects of treatment, year, and treatment × year interaction for the main growth and productivity parameters, indicating a year-dependent fertilization response. Integrated fertilization improved plant height, shoot formation, dry biomass yield, and biofuel output compared with the unfertilized control. The highest mean dry biomass yield was obtained with N30P30K30 + Black Jack, reaching 16.43 t ha−1 and exceeding the control by approximately 40%, while N30P30K30 + Intermag Titan also showed high productivity. Dry biomass yield was strongly associated with plant height, confirming the role of structural development in biomass formation. Economic assessment indicated the highest long-term profitability for N30P30K30 + Black Jack. These findings indicate that integrated fertilization is an effective strategy for sustainable miscanthus biomass production on marginal soils.