Clean recovery and recycling of seasonal surplus forage grass by microbial driven anaerobic fermentation: a case study of napiergrass

Abstract

Abstract In this study, the anaerobic fermentation technique was conducted to accomplish the clean recycling of surplus napiergrass. The surplus napiergrass harvested at two harvest dates (early vegetative stage, NI; late vegetative stage, NII) was treated as follows: (i) natural fermentation of NI (NNI); (ii) natural fermentation of NII (NNII) and stored for 1, 3, 7, 15, 30 and 60 days. After 60 days of anaerobic fermentation, NNI had higher lactic acid concentration and ratio of lactic to acetic acid, but lower pH value and ammonia–nitrogen concentration than NNII. Lactobacillus and Enterobacter were, respectively, dominant in both 7-day NNI and NNII, while Lactobacillus was the most abundant genus in 30-day NNI and NNII. Both harvest date and store time altered the bacterial co-occurrence networks of fresh and fermented napiergrass. The complexity of the bacterial networks decreased from NII, NI, NNII to NNI. The correlations were primarily positive in the bacterial networks of NI, NII, NNII-7 and NNII-30 with positive correlative proportion of 53.0%, 64.3%, 53.1% and 55.6%, but negative in those of NNI-7 (47.4%) and NNI-30 (46.2%) with positive correlative proportion of 47.4% and 46.2%, respectively. Overall, the fermentation quality and microbial community structure of napiergrass during anaerobic fermentation were highly influenced by harvest date and store time. Based on the principle of stable fermentation and high quality, anaerobic fermentation of NI for at least 15 days is recommended. The in-depth understanding of microbial community dynamics and co-occurrence networks during anaerobic fermentation of napiergrass is important for revealing the fermentation mechanism and can contribute to resource recycling without increasing cost. Graphical Abstract

Keywords

• Surplus forage grass
• Harvest date
• Anaerobic fermentation
• Microbial community
• Co-occurrence network
• Recycling