Field scale evaluation of the influence of organic amendments on Miscanthus × giganteus biomass production and soil bioindicators in the marginal degraded land

A field multi-year experiment on the vegetation of Miscanthus × giganteus , a perennial energy crop, in the marginal degraded soil was conducted. The impact of commonly used soil amendments — biochar, sewage sludge, hemicellulose waste, and digestate — was evaluated in terms of plant growth parameters, yield, soil community composition, microbial interactions, and nematode population was assessed. The findings revealed that in the third growing season, M. × giganteus bioparameters increased remarkably, and incorporation of biochar influenced the yield the most. Realization of amendments altered the composition of the soil nematode community, promoting an increase of beneficial trophic groups such as omnivores and predatory nematodes, and reducing the populations of negatively affected plant-parasitic nematodes. Incorporation of biochar, sewage sludge, and digestate positively impacted the key soil microbial groups, particularly bacteria. Sewage sludge and digestate significantly increased bacterial abundance, including nitrogen-fixing bacteria, which in turn enhanced the soil enzymatic activity. Although biochar's incorporation reduced bacterial abundance, it significantly reduced the fungal populations. The lower fungi-to-bacteria ratio determined in biochar-amended soil indicated the bacterial dominance, which correlated with an increase in the proportion of fungivores in nematode community structure. The results highlighted the potential of the studied organic amendments to enhance M. × giganteus performance and soil health during the crop’s vegetation on marginal degraded soil. Future research should focus on long-term monitoring of the impact of amendments on plant development, biomass chemical composition, soil microbial diversity, and carbon sequestration. • Biochar application at 5 % and 10 % doses enhanced M × g biomass yield. • Organic amendments induced substantial shifts in the nematode community structure. • Sewage sludge and digestate increased bacterial populations and soil enzymatic activity. • Biochars reduced fungal populations, promoting bacterial dominance in soil. • Organic amendments supported sustainable management of marginal lands.