# Assessment of Areal Methane Yields from Energy Crops in Ukraine, Best Practices
## 3 Results and Discussion
### Miscantlus  
For biogas production from perennial grasses, harvesting time after the ear-emergence stage is recommended [12]. According to [PERSON] and [PERSON] (2017) [15], the SMY of miscantlus  
Figure 3: Specific methane yield (SMY) and areal methane yield (AMY) of the sweet sorghum varieties harvested at H1, H2 and H3 harvesting times, which correspond to a certain BBCH-code related to a specific stage of crop phenological development. Histograms are charted based on the mean values; error bars indicate the variability between the three replications. Lower case letters indicate significant differences between all the maize samples according to the results of the Tukey test. decreases with later harvesting times, and the AMY obtained from miscanthus is positively correlated with its DMY and SMY. Two varieties of miscanthus bred and patented by the Institute of Bioenergy Crops and Sugar Beet of Ukraine for energy purposes were analysed in this study:  
* Species Giant Chinese Silver Grass: _Miscanthus x giganteus [PERSON] ex [PERSON]_, the variety name \"Osinnii zoretsvit\". We refer to the analysed variety simply as \"Giganteus\". * Species Chinese Silver Grass: _Miscanthus sinensis Anders._, the variety name \"Misiachnyi promin\". We refer to this variety simply as \"Sinensis\". Both analysed miscanthus varieties are recommended for growing in the Polesia and the forest-steppe zones in Ukraine. As it is stated in literature [11; 16; 46], the age of plantation and environmental factors, such as site, climate and weather conditions, have a direct impact on miscanthus yields, furthermore, mature or stabilized crop yields start from second to fourth year of vegetation and last for at least 15 years. The year of vegetation corresponds to the age of miscanthus rhizomes in soil. For this reason, both analysed miscanthus varieties were harvested from the 3 rd vegetation year. For examining whether there is an effect of the age of miscanthus on its SMY and AMY, the miscanthus \"Giganteus\" (variety \"Osinnii zoretsvit\") from the 8 th vegetation year was additionally analysed. The values of DM\({}_{\text{FM}}\), V\({}_{\text{SDM}}\), DMY and crop N uptake are provided in Table 5; the SMY, AMY and BBCH-codes of the miscanthus samples are given in Figure 4.  
The samples were harvested in the period between the stem elongation, booting and before the inflorescence emergence stage (BBCH-codes 36-47). All miscanthus samples had the highest average DM\({}_{\text{FM}}\) (47.80 \(\pm\) 3.29%) when harvested at H3 (BBCH-codes 41-47). The highest average VS\({}_{\text{DM}}\) content (95.13 \(\pm\) 1.90%) was measured for the samples harvested at H2 (BBCH-codes 39-43). All tested varieties showed the highest average DMY (22.12 \(\pm\) 8.57 t\({}_{\text{DM}}\) ha\({}^{-1}\)) during the third harvesting period. However, the DMY values for \"Giganteus\" varied between the samples from different vegetation years. The maximum DMY (30.43 \(\pm\) 0.85 t\({}_{\text{DM}}\) ha\({}^{-1}\)) was determined for \"Giganteus\" from the 8 th vegetation year harvested at H3 (BBCH-code 41). The highest average crop N uptake (104.97 \(\pm\) 33.38 kg\({}_{\text{N}}\) ha\({}^{-1}\)) of miscanthus is related to the H3 harvesting time. Nonetheless, N uptake varied between the varieties: at H3 the uptake for \"Sinensis\" was 66.50 \(\pm\) 1.86 kg\({}_{\text{N}}\) ha\({}^{-1}\) (BBCH-code 47), while for two \"Giganteus\" samples from H3 the determined average crop N uptake was 124.19 \(\pm\) 0.10 kg\({}_{\text{N}}\) ha\({}^{-1}\) (BBCH-code 41). In spite of that, the highest average SMY of 0.26 \(\pm\) 0.04 m\({}^{3}\) kg\({}^{-1}\)VS and the highest average AMY of 4805.44 \(\pm\) 2357.94 m\({}^{3}\) ha\({}^{-1}\) corresponded to the crop samples from H1 (BBCH-codes 36-39). There was also a big difference in SMY between the samples.