Because of the different opinions regarding nitrogen (N) requirements for Miscanthus × giganteus biomass production, we conducted an experiment with a set dose of nitrogen. The objective of this study was to examine the effects of nitrogen fertilization on the biomass yield, water content, and morphological features of rhizomes and aboveground plant parts in various terms during a growing season over the course of three years (2014–2016) in Lower Silesia (Wroclaw, Poland). The nitrogen fertilization (dose 60 kg/ha and control) significantly affected the number of shoots (p = 0.0018), the water concentration of rhizomes (p = 0.0004) and stems (p = 0.0218), the dry matter yield of leaves (p = 0.0000), and the nitrogen uptake (p = 0.0000). Nitrogen fertilization significantly affected the nitrogen uptake in all plant parts (p = 0.0000). Although low levels of nitrogen appeared to be important in maintaining the maximum growth potentials of mature Miscanthus × giganteus, the small reductions in the above- and belowground biomass production are unlikely to outweigh the environmental costs of applying nitrogen. More studies should use the protocols for the above- and belowground yield determination described in this paper in order to create site- and year-specific fertilizer regimes that are optimized for quality and yield for autumn (green) and spring (delayed) harvests.

Fertilisation has a significant impact not only on the yielding, but also on the quality of the harvested biomass. Among energy crops, Miscanthus × giganteus are some of the most important plants used for combustion process. The chemical composition of biomass has significant impact on the quality of combustion biomass. The effect of nitrogen fertilisation (with dose of 60 kg N ha−1) in different terms of biomass sampling on the content and uptake of crude ash, potassium, calcium and sulphur by rhizomes, stems, leaves and the aboveground part of miscanthus was evaluated in the paper. Nitrogen fertilisation contributed to the increase of ash content in the rhizomes and the aboveground part of plants. Independently of nitrogen fertilisation potassium content decreased in the whole vegetation period; in the case of stems this decrease amounted 60%. Calcium content in various parts of plants was highly differentiated compared to potassium content. Average calcium content in the aboveground parts was 2.68 higher compared to rhizomes. Nitrogen fertilisation affected significantly on potassium, calcium and sulphur uptake in all examined parts of plants (except stems in the case of calcium uptake). Uptake of crude ash under nitrogen fertilisation was significantly higher in all examined parts of plants during the whole vegetation period.

This paper presents the effects of nitrogen (N) fertilization on the concentration of selected micronutrients as an important issue in reducing combustion-induced air pollution. We studied the effects of the dose of 60 kg ha−1 N in different terms of biomass sampling on the concentration and uptake of iron (Fe), manganese (Mn), zinc (Zn), and copper (Cu) in the dry matter of the underground and aerial parts of Miscanthus x giganteus in the years 2014–2016. The order of microelement concentrations (mg kg−1) in rhizomes and the aboveground parts of plants was as follows: Fe > Mn > Zn > Cu. N fertilization had no significant effect on the concentrations of the selected microelements in the Mischanthus biomass (except for the Mn concentration in the stems and Cu in the leaves). The results indicated that the quality of the combustion biomass did not worsen under nitrogen fertilization. During the whole vegetation period, the iron concentration increased in the rhizomes and decreased for Zn and Cu. In the aboveground parts of the plant, the concentrations of all tested elements decreased. In turn, the uptake of Fe, Mn, Zn, and Cu (except for Fe in the stems) by rhizomes and the aboveground parts of Mischanthus depended significantly on the N fertilization.