Insight of CO2 and ethanol emission from maize silage: A case study with real-time identification of aerobic and anaerobic microbial respiration using a multi-sensor-fusion method

Abstract

Silage is produced worldwide for both livestock feeding and biogas production. Sustainable silage production requires characterization and mitigation of potential effects on environmental quality, particularly from greenhouse gas emissions during the production cycle. Ex-situ sampling has demonstrated that major emissions are carbon dioxide (CO2) and ethanol (EtOH). In-situ gas measurements from farm silo and bale silage are rare and may be important to improve our knowledge of the physical and biochemical causes, and constraints on these gas emissions. This study focused on tracking the kinetics of CO2 and EtOH emissions from bale maize silage, with real-time identification, quantification and separation of aerobic and anaerobic respiratory components in the period following opening of the silage. For this, an automatic multi-sensor gas-flux chamber (AMGC) was developed. Three bales (mean weight: 890 kg) of maize silage were tested (n = 3). Oxygen (O2) and temperature (Tsi) sensors were co-located at 10- and 20-cm behind the open face of the bales. Over the two weeks of the experiment we observed: (i) significant initial discharge of CO2 across the open face (1.68–2.55 mol m−2 h−1) and EtOH (0.027–0.034 mol m−2 h−1); (ii) peak CO2 emission occurred when O2 concentration (10 cm depth) was 3∼8% vol., while peak EtOH emission occurred below 2% vol. O2, (iii) dynamic conversion of O2 to CO2 from aerobic respiration; and (iv) the cumulative emission of EtOH during the anaerobic period was 4–6 times greater than that during aerobic plus semi-aerobic periods. These novel measurements provide mechanistic understanding, and may facilitate improved management of silage production to minimize environmental impact and aerobic loss of silage.