## 3 Results and Discussion
### Qualitative Parameters of Silage  
The quality of silage prepared in the respective variants was assessed based on the following parameters: content of total solids (TS), proteins, starch, lipids, neutral detergent fiber (NDF), acid detergent fiber (ADF), crude fiber (CF), acid detergent lignin (ADL) and ash (Figure 3). The above parameters were determined at the end of the ensiling process, i.e., when the silage containers were opened. The content of ash ranged, on average, from 7.76% (WSC) to 13.71% (FM). Statistically significant differences were also found between the ash contents of all three variants. It was relatively interesting that the content of ash in the FM + WSC variant significantly decreased compared with the variant in which FM was grown as a sole crop. Thus, growing this crop in a mixed culture may potentially lead to reduced contents of substances, negatively affecting the process of anaerobic digestion (AD). It was a relatively interesting finding that the mixed culture contained less starch and ash in the biomass. Contents of these substances in plants fluctuate in dependence on the plant species, age and organ of the plant [43]. Their concentration mostly ranges from 4% to 8% in the case of ash, while the content of starch is more variable. In fodder crops, for example, it reaches only a few percent in biomass while, in the case of pea, it is >40% and, in cereals, >60% and even more in the grain of the given commodities [44; 45]. The effect of ash content on biogas yield is considerable because its presence in plant biomass (silage) intended for processing by anaerobic digestion reduces the methane production due to  
Figure 3: Qualitative parameters of silage (% TS) (average values of all parameters (\(n=3\)) for one parameter, \(\pm\) SD). FM—fodder mallow, WSC—white sweet clover. its low biodegradability [44]. In contrast, the content of starch in plant biomass positively correlates with the yield of biogas as it is a readily degradable substance [44; 45] which is broken down by microorganisms in the fermenter most quickly, together with sugars [45]. A similar situation was recorded in parameters NDF and ADF too. In WSC, the concentration of these substances was significantly higher when WSC was grown as a sole crop. In the mixed culture, the substances were diluted. NDF content ranged, on average, from 29.06% (FM) to 43.43% (WSC). This value is within the range of results claimed for WSC dry matter by [PERSON] et al. [33]--33.6%--and for dry matter of experimental silage claimed by [PERSON] et al. [24]--48.7%. Statistically significant differences were recorded between all three variants in all three parameters related to the content of fiber in silage. Their values are comparable with the values recorded in maize. Statistically significant differences were recorded between the content of ADL in the variants with WSC and WSC + FM, on the one hand, and FM on the other. The content of proteins as a percentage of dry matter ranged, on average, from 14.48% (WSC) to 16.23% (FM). Statistically significant differences were found between the content of proteins in the variants with WSC and WSC + FM, on the one hand, and FM on the other. In maize, the content of proteins is usually 50% lower than in these variants. Compared with maize (23.73% and 33.30%), the content of starch was, relatively, very low in all three variants and ranged from 6.85% (FM + WSC) to 8.57% (WSC). The lowest content of lipids was recorded in the FM silage (2.62%), and the highest content was in WSC (2.88%). There was no statistically significant difference between the variants. Based on the measured values and their statistical evaluation, it can be stated that differences existed between the tested variants of silages in the following, monitored qualitative parameters: TS (%), ash, NDF, ADF, CF, ADL, proteins and starch. The FM variant of silage contained the most ash and proteins and the least fiber and lignin. In contrast, the WSC variant of silage exhibited the highest contents of fiber (NDF, ADF, CF), starch and ADL.