Impact of Additives and Packing Density on Fermentation Weight Loss, Microbial Diversity, and Fermentation Quality of Rape Straw Silage

To investigate the effects of the combined addition of and sucrose on the fermentation weight loss (FWL), fermentation quality, and microbial community structure of ensiled rape straw under varying packing density conditions. After harvesting, the rapeseed straw was collected, cut into 1-2 cm pieces, and sprayed with sterile water to adjust the moisture content to 60%. The straw was then divided into two groups: one treated with additives (1 × 10 CFU/g fresh material of and 10 kg/t fresh material of sucrose), and the other sprayed with an equivalent amount of sterile water as the control (CK). The treated materials were thoroughly mixed and packed into silos at densities of 450, 500, and 550 kg/m. FWL was recorded on days 1, 3, 6, 15, 20, and 45 of fermentation. On day 45, the samples were analyzed for fermentation quality, microbial counts, and microbial diversity. FWL increased significantly ( < 0.05) in both the treated (LS) and control groups during fermentation. The LS group showed higher lactic acid (LA) levels ( < 0.05) and lower ammonia nitrogen levels ( < 0.05) compared to CK. The CK group had significantly higher ( < 0.05) counts of Coliforms and lower bacterial counts ( < 0.05) than LS. The dominant genera in the silage were , , and . In the LS group, the relative abundances of and ranged from 16.93% to 20.43% and 15.63% to 27.46%, respectively, with their combined abundance being higher than in CK. At a packing density of 500 kg/m, the relative abundances of and in the LS group were significantly higher ( < 0.05) than in CK. Increasing packing density and applying additives to rape straw silage effectively reduced FWL, improved fermentation quality, boosted the relative abundance of beneficial lactic acid bacteria, and decreased the presence of undesirable bacteria such as and .