A new experimental setup for measuring greenhouse gas and volatile organic compound emissions of silage during the aerobic storage period in a special silage respiration chamber

The aim of this study was to develop a new experimental setup to determine parallel the emissions of greenhouse gases (GHG) and volatile organic compounds (VOCs) from silage during the opening as well as the subsequent aerobic storage phase of the complete bale without wrapping film. For this purpose, a special silage respiration chamber was used in which a silage bale could be examined. The gas analysis (CO2, methanol, ethanol, ethyl acetate) of inlet, ambient and outlet air of the silage respiration chamber was carried out by photoacoustic spectroscopy. The gas samples taken inside the bale were analysed by gas chromatography for CO2, O2, CH4, and N2O. Three silage bales (grass and lucerne) as the smallest silage unit commonly used in practice were examined. The emission behaviour of the bales was recorded during experimental periods up to 55 days. The results allow a differentiation of the outgassing processes. On the one hand, gases produced during the anaerobic ensiling process (CO2, CH4, N2O) are released once in a large amount during the first experimental hours after opening the silage. On the other hand, a continuous outgassing process takes place, which is particularly true for the VOCs ethanol, methanol, and ethyl acetate, whereby VOC emissions increase with rising ambient air temperatures. In this study, the emissions during the first 600 experimental hours from the grass silage bale and lucerne silage bale were 2313 g and 2612 g CO2, 17.6 g and 145.2 g methanol, 132.3 g and 675.9 g ethanol, 55.1 g and 66.2 g ethyl acetate, respectively. Nevertheless, the focus of this study was on the technical recording of gas concentrations inside the silage bale itself and the emissions in the ambient air of the bale. For a better interpretation of the data, additional factors should be considered in further investigations.