## 3 Results and Discussion
### Interaction between Silage Parameters and Biogas Yield
\begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline  & **Ash** & **NDF** & **ADF** & **CF** & **ADL** & **Proteins** & **Starch** & **Lipids** & \begin{tabular}{c} **Biogas** \\ **Yield** \\ \end{tabular} & \
\begin{tabular}{c} **Methane** \\ **Yield** \\ \end{tabular} &
\begin{tabular}{c} **Methane** \\ **Content** \\ \end{tabular} \\ \hline Ash & 1.00 & \(-\)1.00 & \(-\)0.99 & \(-\)0.99 & \(-\)0.94 & 0.93 & \(-\)0.52 & \(-\)0.44 & 0.91 & 0.31 & \(-\)0.06 \\ NDF & \(-\)1.00 & 1.00 & 0.99 & 0.99 & 0.93 & \(-\)0.93 & 0.52 & 0.46 & \(-\)0.91 & \(-\)0.30 & 0.06 \\ ADF & \(-\)0.99 & 0.99 & 1.00 & 1.00 & 0.95 & \(-\)0.92 & 0.47 & 0.52 & \(-\)0.89 & \(-\)0.29 & 0.06 \\ CF & \(-\)0.99 & 0.99 & 1.00 & 1.00 & 0.96 & \(-\)0.91 & 0.42 & 0.50 & \(-\)0.88 & \(-\)0.26 & 0.09 \\ ADL & \(-\)0.94 & 0.93 & 0.95 & 0.96 & 1.00 & \(-\)0.85 & 0.43 & 0.63 & \(-\)0.83 & \(-\)0.31 & 0.01 \\ Proteins & 0.93 & \(-\)0.93 & \(-\)0.92 & \(-\)0.91 & \(-\)0.85 & 1.00 & \(-\)0.57 & \(-\)0.31 & 0.87 & 0.52 & \(-\)0.12 \\ Starch & \(-\)0.52 & 0.52 & 0.47 & 0.42 & 0.43 & \(-\)0.57 & 1.00 & 0.21 & \(-\)0.70 & \(-\)0.61 & \(-\)0.59 \\ Lipids & \(-\)0.44 & 0.46 & 0.52 & 0.50 & 0.63 & \(-\)0.31 & 0.21 & 1.00 & \(-\)0.29 & 0.00 & \(-\)0.18 \\ Biogas yield & 0.91 & \(-\)0.91 & \(-\)0.89 & \(-\)0.88 & \(-\)0.83 & 0.87 & \(-\)0.70 & \(-\)0.29 & 1.00 & 0.42 & 0.22 \\ Methane yield & 0.31 & \(-\)0.30 & \(-\)0.29 & \(-\)0.26 & \(-\)0.31 & 0.52 & \(-\)0.61 & 0.00 & 0.42 & 1.00 & 0.42 \\ Methane & \(-\)0.06 & 0.06 & 0.06 & 0.09 & 0.01 & \(-\)0.12 & \(-\)0.59 & \(-\)0.18 & 0.22 & 0.42 & 1.00 \\ content & & & & & & & & & & & \\ \hline \hline \end{tabular} Legend to Table 10: Red color illustrates significant correlations (\(p<0.05\)).  
\end{table} 
Table 10: Correlation matrix from PCA—summary of correlations among the measured parameters. Factor 1 then included yield parameters of biogas, methane and the value of starch parameter, while Factor 2 represented parameters related to major substances in the silage, namely, to fiber, proteins and ash. The diagram projection of the variables on the factor plane (Figure 8) shows to what extent the individual initial variables contributed to the main components (Factor 1 and Factor 2). Factor 1 is apparently the most significant. This is also confirmed by the diagram of eigenvalues (Figure A3), which shows that Factor 1 explains 57.26% of the variability of the measured values. Based on the performed analyses (Tables 10 and 11, Figures 8 and A3), it can be assumed that the factor describes the influence of the source plant biomass on silage quality and biogas production. It can be assumed from the results of the PCA and FA that the methane content in biogas was also affected by an unknown parameter that was not monitored in the experiment. [PERSON] et al. [24] stated, \begin{table}
\begin{tabular}{c c c} \hline \hline
**Variable** & **Factor (1)** & **Factor (2)** \\ \hline Biogas yield & \(-0.71\) & \(0.62\) \\ Methane yield & \(-0.84\) & \(0.00\) \\ Methane content & \(-0.71\) & \(-0.62\) \\ Ash & \(-0.50\) & \(0.78\) \\ NDF & \(0.50\) & \(-0.78\) \\ ADF & \(0.49\) & \(-0.76\) \\ CF & \(0.46\) & \(-0.78\) \\ ADL & \(0.49\) & \(-0.68\) \\ Proteins & \(-0.56\) & \(0.79\) \\ Starch & \(0.84\) & \(-0.09\) \\ Lipids & \(0.20\) & \(-0.09\) \\ \hline \hline \end{tabular}
\end{table} 
Table 11: Results of PCA. Correlation of factors and variables (factor load) according to correlations. Figure 8: Projection of the variables on the factor plane (\(1\times 2\)). NDF—neutral detergent fiber; ADF—acid detergent fiber; CF—crude fiber; ADL—acid detergent lignin. for example, that the coumarin contained in WSC was in a strong negative correlation with the yield of methane and its content in biogas. According to [PERSON] et al. [22], coumarin can be an inhibitory factor in the process of methanogenesis. This was also corroborated by [PERSON] et al. [66], who maintained that this happens only in cases when the microbial community in the fermenter is not adapted to coumarin.