Estimating Herd-Scale Methane Emissions from Cattle in a Feedlot Using Eddy Covariance Measurements and the Carbon Dioxide Tracer Method
Prajapati, Prajaya | Santos, Eduardo A.
Measurements of methane (CH₄) emissions from ruminants could provide invaluable data to reduce uncertainties in the global CH₄ budget and to evaluate mitigation strategies to lower greenhouse gas emissions. The main objective of this study was to evaluate a new CO₂ tracer (CO₂T) approach that combined CH₄ and CO₂ atmospheric concentrations with eddy covariance (EC) CO₂ flux measurements to estimate CH₄ emissions from cattle in a feedlot. A closed-path EC system was used to measure CH₄ and CO₂ fluxes from a feedlot in Kansas. The EC flux measurements were scaled from landscape to animal scale using footprint analyses. Emissions of CH₄ from the cattle were also estimated using the CO₂T approach and measured CO₂ and CH₄ concentration, and scaled EC CO₂ fluxes. The CH₄ and CO₂ concentration ratios showed a distinct diel trend with greater values during the daytime. Average monthly CH₄ emission estimates using the CO₂T approach ranged from 72 to 127 g animal⁻¹ d⁻¹, which was consistent with the values reported in other studies that had similar animal characteristics. The CO₂T method CH₄ emission estimates showed good agreement with scaled CH₄ EC fluxes (slope = 0.9 and R² = 0.8) for cold and dry months. However, the agreement between the two techniques was significantly reduced (slope = 1.5 and R² = 0.6) during wet and warm months. On average, the CO₂T method CH₄ emission estimates were 3% greater than the EC CH₄ emissions. Overall, our results suggest that the CO₂T method can be used to estimate enteric feedlot CH₄ emissions.Show more [+] Less [-]