## 3 Results and Discussion
### Methane Content in Biogas  
The average values of methane (CH4) content in biogas in the respective variants of silage and their statistical analysis are presented in Table 9. There were no statistically significant differences between the recorded values of methane in biogas. The measured values, once again, do not confirm the hypothesis that the growing of FM and WSC in a mixed culture leads to the increased production and quality of biogas.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Variants** & **FM** & **WSC** & **FM + WSC** \\ \hline Mean & CH4 = 68.7\% vol a & CH4 = 68.5\% vol a & CH4 = 69.5\% vol a \\ \hline \hline \end{tabular}
\end{table}
Table 9: Results of [PERSON]’s HSD test for the parameter of average methane content in biogas after 35 days of the experiment.  
Figure 6: Methane yield based on the yield of fresh biomass (mean of measured values (\(n\) = 3) \(\pm\) SD). FM—folder mallow, WSC—white sweet clover. Different capital letters indicate significant differences (\(p\) < 0.05).  
Figure 7 shows the process of methane concentration in biogas developing for 35 days. The courses of the curves in the respective variants indicate similarity with courses of methane yield values (Figure 5); the differences between the variants were, however, non-significant. The highest values of methane content were recorded until the ninth day of measurements in the WSC variant. From the tenth day of measurements, differences in the content of methane were very small between the variants (up to a maximum of 1%) and statistically non-significant. The measured values suggest that the individual crops both in monocultures and in the mixed culture produced silage quality which had no adverse effect on the content of methane in biogas. It is interesting that the FM + WSC variant, i.e., biomass grown in the MC regime, almost did not show any difference from the variants with silages made of sole-grown crops from Day 12. This confirms that, if we use biomass combined from more crops, we can achieve a production of biogas that is of the same quality in terms of methane content as that from the silage of sole crops. This opens the way for possible use of multiple plant species (from different families) in the production of silage for biogas. According to [PERSON] et al. [61], the content of methane in biogas is influenced by the course of the reaction of carbon dioxide with hydrogen, decomposition of acetic acid, by temperature, pH, etc. A significant influence in the production of methane is also that of suitable inoculum, particularly in the initial phases of the biogas production [62]. These factors can reduce the production of methane or even stop it in extreme cases. This, however, did not happen in the case of tested silages. [PERSON] et al. [24] reported that an average concentration of methane in biogas reached 52.3% after 21 days in the WSC monosubstrate. In this experiment, the methane concentration after 21 days amounted to 69.0%, i.e., 31.9% more. However, not even that difference contributed to the confirmation of the tested hypothesis. The influence of the chemical composition of biomass entering the AD process on the quality of produced biogas was also corroborated by [PERSON] et al. [63], who even claimed in their work that the use of grasses and legumes is possible and desirable because these plant species contribute to the sustainability of biogas production from the plant biomass.  
Figure 7: Methane content in biogas during 35 days of the experiment (average values for every day of measurement (\(n=3\)) for one measurement, \(\pm\)SD). FM—fodder mallow; WSC—white sweet clover.