Improving the quality of Napier grass silage with pyroligneous acid: Fermentation, aerobic stability, and microbial communities

The presence of undesirable microorganisms in silage always leads to poor fermentation quality and low aerobic stability. Pyroligneous acid (PA), a by-product of biochar production, is known to have strong antimicrobial and antioxidant activities. To investigate the effects of PA on fermentation characteristics, aerobic stability, and microbial communities, Napier grass was ensiled with or without 1 and 2% PA for 30 days and then aerobically stored for 5 days. The results showed that PA application decreased (P < 0.01) the pH value, ammonia nitrogen content, and number of undesirable microorganisms (coliform bacteria, yeasts, and molds) after 30 days of ensiling and 5 days of exposure to air. The temperature of the PA-treated group was stable during the 5-day aerobic test, which did not exceed room temperature more than 2 degrees C. The addition of PA also enhanced the relative abundance of Lactobacillus and reduced that of Klebsiella and Kosakonia. The relative abundance of Candida was higher in PA-treated silage than in untreated silage. The addition of PA decreased the relative abundance of Kodamaea and increased that of Monascus after 5 days of exposure to air. The abundances of Cladosporium and Neurospora were relatively high in 2% PA-treated NG, while these genera were note observed in the control group. These results suggested that the addition of PA could improve fermentation characteristics and aerobic stability, and alter microbial communities of silage.