## 3 Results and Discussion  
The basic elements that should be met when selecting a plant for biomass production are a high yield of biomass, an appropriate calorific value of the biomass, and the appropriate selection of species for the given habitat conditions [19; 22; 33; 43; 44; 45; 46; 47; 48]. Moreover, according to some authors, the criteria for assessing plants as a raw material for energy production also depend on the form of energy that the grower intends to obtain (e.g., heat, electricity) and the biomass conversion technology that will be used (e.g., direct combustion, gasification or pyrolysis) [4; 12; 21; 49; 50; 51; 52; 53]. In our own research conducted from 2010 to 2016, the production possibilities of reed canary grass for energy purposes were assessed depending on the moving date and the age of the plantation. This article uses the results obtained for the seasons of 2010/2011 (annual plantation), 2012/2013 (three-year plantation), and 2015/2016 (six-year plantation) (Table 2). In each research season, a two-cut system was used for reed canary grass biomass harvesting (summer/winter). In the 2010/2011 season (annual plantation), during the summer harvest, the biomass yield was 2.40 t\(\cdot\)ha\({}^{-1}\), and during the winter harvest, the yield was 1.45 t\(\cdot\)ha\({}^{-1}\). The total biomass yield of reed canary grass for the 2010/2011 season  
Figure 5: Summer (**A**) and winter (**B**) harvest of reed canary grass. (annual plantation) was 3.85 t\(\cdot\)ha\({}^{-1}\). In the 2012/2013 season (three-year plantation), the biomass yield was, respectively: 6.65 t\(\cdot\)ha\({}^{-1}\) for the summer harvest and 1.85 t\(\cdot\)ha\({}^{-1}\) for the winter harvest. The total biomass yield for the 2012/2013 season (three-year plantation) was 8.50 t\(\cdot\)ha\({}^{-1}\). However, in the 2015/2016 season (six-year plantation), the biomass yield obtained was, respectively: 6.10 t\(\cdot\)ha\({}^{-1}\) for the summer harvest and 2.65 t\(\cdot\)ha\({}^{-1}\) for the winter harvest. The total biomass yield for the 2015/2016 season (six-year plantation) was the highest and amounted to 8.75 t\(\cdot\)ha\({}^{-1}\). The obtained observations show that the highest biomass yields were obtained from the summer harvest from the three-year plantation, and the difference was statistically significant compared to the yields obtained from the annual and six-year plantation. On the other hand, the winter harvest was characterized by a significantly lower biomass yield compared to the summer harvest (regardless of the age of the plantation). On the other hand, after summing up the biomass yields from the two cuts for each research season separately, it was found that the biomass yield from the annual plantation (season 2010/2011) was the lowest compared to the yields obtained from the three-year plantation (season 2012/2013) and the six-year plantation (season 2015/2016), which was statistically confirmed. On the other hand, the total biomass yields obtained from the three-year and six-year plantations were at a similar level and did not differ statistically. Similar research results regarding the size of the yield depending on the age of the plantation were obtained by other authors in dealing with the subject of obtaining biomass from various plants intended for energy purposes [33; 51; 54; 55]. The yield of need canary grass is different in natural areas of canary grass meadows, floodpolains, and river valleys. Natural canary grass meadows in river valleys are a remnant of former marsh ecosystems. Therefore, the biomass yield from such natural canary grass beds is largely dependent on the percentage of reed canary grass in the plant community [15]. A study conducted by [PERSON] et al. [30] shows that biomass yields obtained from natural canary grass meadows ranged from 5.80 to 6.70 t\(\cdot\)ha\({}^{-1}\) and were significantly lower than yields obtained from intentionally established reed canary grass plantations. Similar conclusions were reached by [PERSON] et al.