## 3 Results and Discussion
(2019), the yield and content of macro- and micro-elements and the energy value of canary grass biomass depend to a large extent on the harvest date, abundance, type of habitat, and use (intentionally established plantations or natural meadow areas of canary grass). Similar research results concerning the content of macro- and micro-elements in the biomass of need canary grass were obtained by [PERSON] and [PERSON] (2017), [PERSON] (2019), and [PERSON] et al. (2016). Also, the research conducted by [PERSON] et al. (2019) shows that the highest contents of nitrogen (2.32% d.m. ), potassium (1.59% d.m. ), and calcium (0.69% d.m.) were obtained from reed canary grass collected in the summer. On the other hand, the research conducted by [PERSON] et al. (2017) shows that the average nitrogen content in the biomass of reed canary grass collected in the winter was lower and amounted to 1.17% d.m., and that the average sulfur content was higher and amounted to 0.27% d.m. Figure 6: Nitrate (N, (**A**)) and phosphorus (P, (**B**)) content in the biomass of reed canary grass (_P. arundinacea_) and its variability depending on the harvest date and plantation age. Means followed by same letter or symbol do not significantly differ (_p_ = 0.05, Tukey’s HSD). Nitrate: interaction years \(\times\) harvest time = 0.145, standard deviation = 0.051. Phosphorus: interaction years \(\times\) harvest time = 0.666, standard deviation = 0.235. A problem during the combustion of biomass obtained from several-year-old reed canary grass plantations may be its high chlorine content, which, over time, may cause the so-called slagging and sintering of the grates. In our own studies, the chlorine content in the collected reed canary grass biomass depended on the age of the plantation and the harvest date. The highest statistically confirmed chlorine content was found in the biomass obtained from the summer harvests from the six-year-old plantation (0.83% d.m.) and the three-year plantation (0.78% d.m.). On the other hand, the lowest amount of chlorine (0.067% d.m.) was contained in the biomass harvested in the winter period from the six-year-old plantation. Our own studies show that the chlorine content was the most dependent on the age of the plantation and the harvest date of reed canary grass. The results of our own research on the chlorine content in the biomass of reed canary grass were similar to those obtained by [PERSON] and [PERSON] (2017), [PERSON] (2017), and [PERSON] et al. (2018). Moreover, the research conducted by [PERSON] et al. (2018) shows that it is  
Figure 8: Magnesium (Mg, **(A)**) and sodium (Na, **(B)**) content in the biomass of reed canary grass (_P. arundinacea_) and its variability depending on the harvest date and plantation age. Means followed by same letter or symbol do not significantly differ (_p_ = 0.05, [PERSON]’s HSD). Magnesium: interaction years \(\times\) harvest time = 0.059, standard deviation = 0.021. Sodium: interaction years \(\times\) harvest time = 0.0110, standard deviation = 0.0039. Figure 7: Potassium (K, **(A)**) and calcium (Ca, **(B)**) content in the biomass of reed canary grass (_P. arundinacea_) and its variability depending on the harvest date and plantation age. Means followed by same letter or symbol do not significantly differ (_p_ = 0.05, [PERSON]’s HSD). Potassium: interaction years \(\times\) harvest time = 0.232, standard deviation = 0.082. Calcium: interaction years \(\times\) harvest time = 0.108, standard deviation = 0.038.  
possible to obtain biomass from reed canary grass with a four-fold lower chlorine content by harvesting it in the spring of the following year, at which point the average chlorine content drops from 0.795% d.m. to 0.21% d.m. The results of these authors were confirmed by our own research, which shows that, for the winter harvests, the average chlorine content in each subsequent year dropped, reaching values from 0.091% d.m. (one-year plantation) to 0.067% d.m. (six-year plantation) (Figure 9B).