NMVOC, CH4 and NH3 emissions of different silage-based diets for dairy cows at herd level
Agricultural activities, such as dairy cattle farming in perticular, make a substantial contribution to the Swiss methane (CH4) and ammonia (NH3) emissions [1, 2]. In addition, dairy farming is also a relevant source for non-methane volatile organic compounds (NMVOCs) . Since summer 2015, Agroscope and Empa assess CH4, NH3 and CO2 emissions from dairy cows at the experimental housing for emission measurements, Waldegg, Switzerland . The housing consists of two spatially separated compartments, each for 20 cows, which allows comparative quantification of emissions simultaneously. A dual tracer-ratio method with SF6 and SF5CF3 is applied to determine emissions under natural ventilation and detect cross-contamination . For two years, 2018 and 2020, the focus was additionally on NMVOC emissions under different feeding regimes, silage-based vs. silage-free (2018) and different silage types with and without additives (2020). NMVOC emissions were determined using different analytical techniques, such as gas chromatography with flame ionisation detector (GC-FID) and a total hydrocarbon monitor (THC), while C4, CO2 and NH3 concentrations were quantified using cavity ring down spectroscopy. NMVOC emissions in the compartments with the silage-based diet were generally dominated by ethanol followed by methanol and ethyl acetate. Summer measurements showed around 70% lower ethanol emissions in the compartment with the silage-free diet compared to the silage-based diet. In autumn and winter, ethanol emissions in the silage-free compartment were even lower - in the range or below the detection limit. Based on the collected NMVOC emission data, the statistical model and metrological data from MeteoSchweiz we established a model-based calculation to estimate yearly NMVOC emissions for dairy cattle in mountain and plain regions under different feeding regimes.
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