# Assessment of Areal Methane Yields from Energy Crops in Ukraine, Best Practices
## 1 Introduction  
In 2018, the natural gas import in Ukraine amounted to 35.7% of the total gas consumption [1]. The topical issue is to reduce the natural gas import, which can be done through the production of biogas. According to [PERSON] et al. [2], the biogas production in Ukraine in 2015 sums up to 600 TJ or 117 mil m\({}^{3}\), while the biogas share in the natural gas use was only 0.1%. In 2018 this share increased to 0.2% [1]. End of 2019, the installed power capacity of biogas plants in Ukraine amounted to 70 MW power capacity, where 47 MW of these units are based on agricultural wastes and the remaining run on landfill gas [3].  
In the development of Ukraine's biogas sector, the availability of feedstock plays one of the key roles. As of February 2020, the existing agricultural biogas plants in Ukraine utilize the following substrates: pig and cattle manure, poultry litter, sugar-beet pulp, sugar sorghum silage and maize silage. It is noteworthy that in Ukraine there is a limited amount of manure due to a constant decreasing trend in livestock breeding except for poultry [1]. Therefore, alternative biogas substrates other than manure or poultry litter should be investigated.  
To provide continuous availability of substrates supplies in biogas plants, different bioenergy crops cultivated in Ukraine specifically for biogas production can be utilized. Currently, Ukraine does not have a deficiency in the food crops availability which is in correspondence to its relatively low population density of 69.49 inhabitants per km\({}^{2}\) (in Germany the population density is 233, in China--146); moreover, Ukraine is one of the leading grain exporting nations in the world [1; 4]. As the area of agricultural lands in Ukraine as of 01.01.2016 amounted to 42,726.4 thousand hectares or 70.8% of the total area of Ukraine [5], a part of bioenergy crops can be grown on underutilized agricultural lands or in sustainable rotations with other crops. Furthermore, experts assess the area of marginal lands in Ukraine to be \(\sim\)4 million hectares for the inland territory [6; 7], where the bioenergy crops can be additionally cultivated. Therefore, due to the land's availability, bioenergy crops are a potentially attractive substrate for biogas production in Ukraine. Additionally, since December 2019 the State Agency on Energy Efficiency and Energy Saving of Ukraine has been requesting the approval of the amendments to the Ukrainian legislation that should provide a state support program for the cultivation of bioenergy crops [8].  
The biogas production from bioenergy crops is directly related to the value of crop's areal methane yield (AMY), measured in m\({}^{3}\)CH\({}^{4}\)-ha\({}^{-1}\)[9]. For bioenergy crops, the AMY depends on many parameters: crop species [9; 10; 11], crop variety [12; 13; 14], soil-climatic conditions [11], average temperature and precipitation during the cultivation period [15; 16; 17; 18], dosage of fertilizer applied [16; 19; 20], harvesting time related to specific stages of crop phenological development [9; 11; 12; 13; 14; 15; 19; 21; 22; 23; 24], pretreatment, especially for lignocellulosic biomass [23; 25; 26; 27; 28] among others.  
No literature was found on AMY of bioenergy crops grown in Ukraine. Since the soils and climatic conditions in Ukraine differ significantly from those of Western European countries, the experience gained in energy crops cultivation in these countries cannot be directly transferred to Ukraine. For this reason, the study on the assessment of AMY of high-yield bioenergy crops grown in Ukraine has to be conducted.  
In this study, the effects of harvesting time and vegetation year (for perennials) on AMY of potential Ukrainian energy crops are studied. Additionally, the effects of dry matter yield (DMY) and crop N uptake on AMY are determined.