## 4 Conclusions  
The biomass yield obtained from a purposefully established reed canary grass plantation depended on the harvest date and the age of the plantation. The highest total biomass yield of 8.75 t\(\cdot\)ha\({}^{-1}\) was obtained from a six-year-old plantation. The lowest total biomass yield of 3.85 t\(\cdot\)ha\({}^{-1}\) was obtained from a one-year plantation. The harvest date (summer/winter) also influenced the biomass yield. The yield obtained in the summer period was always higher (average for summer seasons was 5.05 t\(\cdot\)ha\({}^{-1}\)) than the yield obtained from the winter harvest (average for winter seasons was 1.98 t\(\cdot\)ha\({}^{-1}\)). The contents of some elements in the biomass also depended on the age of the plantation and the harvest date. An example is nitrogen (1.97% d.m.) and potassium (2.35% d.m. ), the largest amounts of which were found in biomass collected in the summer from the one-year plantation. On the other hand, the highest chlorine content was found in biomass obtained from the summer harvest from the six-year plantation (0.83% d.m.). The moisture and ash content of the obtained biomass also depended on the age of the plantation and the harvest date. The highest moisture content (12.5%) was characteristic of biomass collected in the summer from the one-year plantation. On the other hand, the lowest moisture content was found for biomass collected in the winter from the six-year plantation. The most ash was obtained from biomass collected in the summer from the annual plantation (75 g\(\cdot\)kg\({}^{-1}\) d.m.) and the lowest amount was obtained from the winter harvest from the six-year plantation (45 g\(\cdot\)kg\({}^{-1}\) d.m.). The highest calorific value of 16.2 MJ\(\cdot\)kg\({}^{-1}\) d.m. and a combustion heat of 17.5 MJ\(\cdot\)kg\({}^{-1}\) d.m. were characteristic of the biomass obtained from the winter harvest from the six-year plantation. The total biomass yield obtained from the three-year plantation (8.50 t\(\cdot\)ha\({}^{-1}\)) and six-year plantation (8.75 t\(\cdot\)ha\({}^{-1}\)), as well as the average ash content (58-52 g\(\cdot\)kg\({}^{-1}\) d.m. ), average moisture (9.3-8.75%), average calorific value (15.5-16.1 t\(\cdot\)ha\({}^{-1}\)), and average combustion heat (16.9-17.25 t\(\cdot\)ha\({}^{-1}\)) of reed canary grass biomass confirm its suitability as an energy resource. A problem during the combustion of biomass obtained from several-year-old plantations may be its high chlorine content (0.426-0.449%), which, over time, may cause the so-called slagging and sintering of grates. One of the solutions to counteract this unfavorable phenomenon is following the proper regulations recommended by the boiler manufacturer, which usually consist of the appropriate configuration of the deflector and the fuel feeding time. In the case of solid fuel with high chlorine and sulfur contents, the technical break in feeding further portions of fuel should be 5 s.  
In order to supplement the research in the following years, it is planned to establish a three-year rigorous experiment, the aim of which will be to demonstrate the effect of  
Figure 11: Calorific value (**A**) and heat of combustion (**B**) of reed canary grass (_P. arundinaca_) biomass depending on the harvest time and plantation age. Means followed by same letter or symbol do not significantly differ (_p_ = 0.05, [PERSON]’s HSD). Calorific value: interaction years \(\times\) harvest time = 0.82; standard deviation = 0.29. Heat of combustion: interaction years \(\times\) harvest time = 0.74; standard deviation = 0.26.  
differentiated fertilization on different development stages of selected canary grass varieties in terms of their yield, the quality of their biomass for energy purposes, and the economic and energy efficiency of their production. Conceptualization, T.R.S. ; methodology, T.R.S. and J.G. ; validation, T.R.S. and M.Z. ; formal analysis, T.R.S. and J.B. investigation, T.R.S. ; resources T.R.S. ; writing--original draft preparation, T.R.S. and J.G.