Determining characteristics of CO2 and ethanol emissions from microbial respiration in silage by partitioning of aerobic/anaerobic metabolites

To investigate potential pollution of silage production to environment, we developed a multi-sensor-based instrument for tracking of carbon dioxide (CO 2 ) and ethanol (EtOH) emissions from feed-out silage, incorporated real-time monitor of oxygen (O 2 ) concentration to distinguish different metabolic sources, and combined measurements of silage temperature (T si ）and pH to identify aerobic-stability and microbial-activity. Two common silage materials (maize and ryegrass), as experimental mini-silos treated either with or without a commercial bio-additive, were fermented in 1.5-L glass jars. The test, started immediately exposing samples to air, lasted 320 h (maize) or 600 h (ryegrass). The achieved data demonstrate: (i) all samples underwent from aerobic-stable to unstable processes; (ii) the initial emissions of CO 2 and EtOH (0 ~ 10 h of aerobic-stable period) yielded mainly from anaerobic metabolism (maize, CO 2 : 1.104 1.294, EtOH: (0.570 0.807) × 10 -2 ; ryegrass, CO 2 : 0.805 0.888, EtOH: (0.060 0.408) × 10 -2 , unit: mol m -2 ), the end-products of preceding fermentation by heterofermentative lactic acid bacteria (LAB) and subsequently accumulated in the sealed jars; (iii), after samples became unstable, the emission of CO 2 represented a mixture of aerobic and anaerobic metabolites, whereas EtOH was anaerobic one, both compounds by yeasts; and (iv) time lags (maize: ca. 40 h, ryegrass: ca. 100 h) between CO 2 and EtOH emissions were observed during the aerobic-unstable period. These findings contribute to our understandings of aerobic deterioration in silage and resulting pollution to air, providing supports for optimization of on-farm silo management to minimize the gas/VOC emissions from silage production. • Multi-sensor-fusion innovation to track CO 2 and ethanol (EtOH) emissions from silage • In situ O 2 -trace classification of aerobic (CO 2 ) and anaerobic (Ethanol) metabolites • Emission characteristics of CO 2 and EtOH determined from maize and ryegrass ensiling • EtOH is an anaerobic metabolite but can be produced by yeast during silage feed-out • Maize/Grass initial-emit: CO 2 1.1 1.3, 0.8 0.9; EtOH (0.6 0.8, 0.1 0.4)×10 -2 , mol m -2