Cultivar-Dependent Differences in Agronomic Characteristics, Nutritional Value, Fermentation Quality, and Bacteriome Profile of Whole-Plant Sorghum Silage

Forage scarcity in semi-arid regions necessitates the identification of optimal sorghum cultivars for high-quality silage production. This study systematically evaluated varietal differences in agronomic characteristics, nutritive value, fermentation quality, and bacterial community structure of whole-plant sorghum silage. A completely randomized design was implemented with four sorghum cultivars representative of semi-arid northwestern China: Liaotian1 (LT1), Jinnuo3 (JN3), Jinza2001 (JZ2001), and Jinza1531 (JZ1531). Five quadrats per cultivar in experimental fields were randomly designated as biological replicates for silage production. The plants were harvested at the dough stage, chopped, and ensiled in laboratory-scale silos (n = 20, 4 cultivars × 5 replicates) for 120 days. Analyses included agronomic measurements, chemical composition, fermentation parameters, microbial plate enumeration, and bacterial community profiling via 16S rRNA gene amplicon sequencing of the V3-V4 hypervariable region. The results showed that cultivar significantly influenced (p < 0.01) all agronomic traits and most nutritional parameters. The forage-type cultivar LT1 showed the highest biomass yield but the lowest nutritional quality, with higher neutral detergent fiber (47.77% vs. 29.21-32.35%; p < 0.05) and lower starch (10.94% vs. 18.10-24.30%; p < 0.05) contents as well as higher dry matter losses (1.39% vs. 0.91-1.23%; p < 0.05) than grain-type cultivars. In contrast, the grain-type cultivar JN3 exhibited balanced yield-quality traits with the highest (p < 0.05) starch (24.30%) and crude protein (7.50%) contents. Most fermentation parameters differed significantly (p < 0.01) among cultivars, with JN3 showing elevated ammonia-nitrogen (0.24 g/kg) but within acceptable ranges. Microbial diversity analysis revealed cultivar-driven differences in bacterial communities, with JN3 enriched in Leuconostoc and early-colonizing taxa (p < 0.05 and LDA Score > 4). It is concluded that the grain-type cultivar JN3 is the most suitable cultivar for whole-plant sorghum silage production in water-limited regions due to its optimal yield-quality balance. The findings underscore the importance of integrated cultivar evaluation and suggest the potential of targeted microbial inoculants for enhancing silage quality.