## 1 Introduction  
One of the main goals of the EU's policy to mitigate climate change and increase energy security in Europe is to gradually move away from fossil fuels towards renewable energy sources [1; 2; 3; 4].  
The European Union assumed that, by 2030, at least 32% of the energy produced in Europe will come from renewable sources [2]. Unfortunately, the events of the last 2 years (the war in Ukraine) and a significant reduction in the share of Russian fossil fuels in the EU's energy structure have led to a revision of the previous assumptions. Currently, the new EU goal is to achieve 42.5% of its energy from renewable sources by 2030 [5]. In the EU, the most important renewable energy sources are solid biofuels, which account for 41% of the total renewable energy globally [5]. Also, in Poland, most energy production from renewable sources comes from solid biofuels, which account for as much as 69.3% of the overall renewable energy balance [6; 7]. In Poland, the most important renewable energy source in the production of renewable energy is biomass obtained from various plants, mainly non-agricultural ones. Moreover, wind, water, and solar energy also play an important role in the overall energy balance [8; 9; 10; 11].  
However, biomass is considered the least capital-intensive and most promising source of renewable energy, being the so-called \"neutral fuel\", precisely due to its low greenhouse gas emissions [12; 13]. So-called non-agricultural plant species can be used to produce biomass. These are species that accumulate an appropriate amount of lignocellulosic as a starting product for the production of energy carriers that are solid (e.g., wood chips, pellets, briquettes), gaseous, or liquid (e.g., biogas or bioethanol) [14; 15]. The high ecological plasticity of such species creates the possibility of using them to produce biomass for energy purposes in various habitats [10; 11; 16; 17; 18; 19; 20; 21; 22].  
The most commonly used species for this purpose are: _Salix_ sp., _Populus_ sp., _Robinia pseudoaccia_, _Sida hermaphrodita_, _Miscanthus x giganteus_, _Spartina pectinata_, and _Panicum virgatum_. In addition to the mentioned species, other species are also used, e.g., grass species, which include reed canary grass (_Phalaris arundinacea_). Due to its physicochemical properties and high efficiency, as well as the relatively low financial outlays for establishing a reed canary grass plantation, this species can be successfully used for biomass production [23; 24; 25; 26].  
Reed canary grass (_P. arundinacea_) occurs commonly in the wild in the temperate climate zones of North America, Asia, and Europe [27]. It is a hydro- and nitro-philous species, and is very well tolerant of even long-term surface flooding and periodic droughts. In Poland, it is found in its natural state, especially on fertile floodplains, and was also a common component of meadow sward. Due to its production of large amounts of biomass, it is used for energy production, e.g., for direct combustion and the production of biofuels and biogas [28; 29; 30; 31; 32; 33; 34].  
This research on the possibilities of obtaining biomass from reed canary grass may contribute to obtaining the necessary information on yields depending on the age of the plantation and the harvest date, as well as the possibilities of using biomass for energy purposes.  
The aim of this study was to assess the effects of the harvest date and plantation age on the yield, chemical composition, and calorific value of reed canary grass (_P. arundinacea_) intended for energy purposes.