The Effect of Lactobacillus planturum YQM48 Inoculation on the Quality and Microbial Community Structure of Alfalfa Silage Cultured in Saline-Alkali Soil

Alfalfa cultivated in salt–alkali soil was used for fermentation, to which an inoculum of Lactobacillus plantarum YQM48 was added, to assess its effect on the feed quality and the microbial community structure of the fermented silage. A control was included without inoculum. The nutritional components, fermentation quality, pH, and microbial community of the silage were measured after 30 and 60 days of anaerobic fermentation. The results showed that after 30 and 60 days of fermentation in the presence of the inoculum, the content of water-soluble carbohydrates, crude protein content, and dry matter were all significantly higher than those of the control silage, the pH and butyric acid content were lower, and the content of lactic acid and acetic acid were higher (p < 0.05 for all). There was no significant difference in pH and butyric acid content between 30 and 60 days of fermentation in the presence of the inoculum (p > 0.05), while the lactic acid and acetic acid contents were significantly lower in the 60-day silage compared to the 30-day silage (p < 0.05). Fermentation reduced the abundance of Cyanobacteria and Proteobacteria (the abundant phyla in the fresh alfalfa), while the abundance of Firmicutes increased, reaching 92.3% after 60 days of fermentation with inoculum. The dominant genus in that sample was Lactobacillus (70.0%), followed by Enterococcus (12.9%), while fermentation of 60 days without inoculum resulted in only 29.2% Lactobacillus, together with 27.8% Cyanobacteria, and 12.2% Enterococcus. In summary, the addition of L. plantarum YQM48 can improve the nutritional components and fermentation quality of alfalfa silage cultivated on a salt-alkali soil.