## 3 Results and Discussion
### Methane Yield  
The production of methane was ascertained along with the biogas production. Methane yields did not show any statistically significant differences between the tested variants (Table 8). The highest production of methane was recorded in the silage of mixed FM + WSC culture (50:50). The total yield for the 35 days of the experiment duration amounted to 0.30 m\({}^{3}\)/kg\({}_{\rm VS}\). However, a statistically significant difference in the production of methane between the respective samples could not be confirmed. Thus, the values do not confirm our hypothesis that the growing of selected plants in a mixed culture contributes to the increased production of methane compared with the situation when they are grown in monocultures. During the first seven days, the methane yield produced was between 69.9% (WSC) and 75.6% (FM) of total methane yield recorded for the 35 days of the experiment duration; this, however, did not have a statistical effect in the overall comparison of measured values. The cumulative production of methane during the 35 days in all three silage variants is presented graphically in Figure 5.  
The diagram in Figure 5 shows that the lowest average methane yield was already recorded in the WSC silage on the second day of measurements. The total yield in this variant (Table 8) was 0.27 m\({}^{3}\)/kg\({}_{\rm VS}\). After 21 days, the yield was 0.25 m\({}^{3}\)/kg\({}_{\rm VS}\), which is 56% higher than reported by [PERSON] et al. [24]--their average yield after 21 days of experiment duration was 0.16 m\({}^{3}\)/kg\({}_{\rm VS}\) in WSC. A non-significant, higher average yield was recorded throughout the measurements in the FM silage in which the total average yield reached 0.29 m\({}^{3}\)/kg\({}_{\rm VS}\). The, again, non-significant, highest production of methane was already recorded from the third day of the experiment in the silage from the mixed FM + WSC (50:50) culture in which the total yield was 0.30 m\({}^{3}\)/kg\({}_{\rm VS}\). This was 3% more than the yield recorded in the FM variant and nearly 10% (9.47%) more than the yield recorded in the WSC variant, i.e., on average, 6.2% more than the yield of both monosubstrates. Unfortunately, these differences were not significant (Table 8). The reason was a high variability of measured values, which is also obvious from the range of error bars presenting the size of the SD (Figure 5). \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Variants** & **FM** & **WSC** & **FM + WSC** \\ \hline Mean & 0.600 a  \(\rm m^{3}/kg_{\rm VS}\) & 0.474 b  \(\rm m^{3}/kg_{\rm VS}\) & 0.544 c  \(\rm m^{3}/kg_{\rm VS}\) \\ \hline \hline Legend to Table 7: Different small letters illustrate demonstrable differences between the respective experimental treatments at a level of significance \(p<0.05\). FM—folder mallow, WSC—white sweet clover. & & \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Results of [PERSON]’s HSD test for the parameter of average biogas yield after 35 days of the experiment. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Variants** & **FM** & **WSC** & **FM + WSC** \\ \hline Mean & 0.294 a  \(\rm m^{3}/kg_{\rm VS}\) & 0.274 a  \(\rm m^{3}/kg_{\rm VS}\) & 0.303 a  \(\rm m^{3}/kg_{\rm VS}\) \\ \hline Legend to Table 8: Different small letters illustrate demonstrable differences between the respective experimental treatments at a level of significance \(p<0.05\). FM—folder mallow, WSC—white sweet clover. & \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Results of [PERSON]’s HSD test for the parameter of average methane yield after 35 days of the experiment. Figure 6 shows the yield of methane determined on the basis of green biomass yield per unit area. Regarding the fact that no statistically significant differences existed between the methane yields of all three silage variants, it can be assumed that all three variants of silage would exhibit a similar performance in the production of electric energy.