Diurnal Variation in Greenhouse Fluxes from a Feedyard Pen Surface.

Accurate estimation of greenhouse gas (GHG) emissions, including nitrous oxide (N₂O) and methane (CH₄) from open-lot beef cattle feedlots is an increasing concern given the current and potential future reporting requirements for GHG emissions. Research concerning N₂O and CH₄ emission fluxes from the manure management system at feedlots, however, has been very limited. This study was conducted to quantify the diel variation N₂O and CH₄ flux rates from pen surfaces at a commercial beef cattle feedlot in Texas during 2017. Fluxes from pen surfaces were measured hourly using Licor Long-Term Chambers (8100-104) on 5 sampling days during summer, in a 5-d measurement campaign. Six chambers were arranged in two rows of three, strategically covering representative areas of the pen, including areas near feedbunks and water troughs. A custom built multiplexer sequenced air from each chamber to a Los Gatos Research Enhanced Performance Model N₂O/CO analyzer (913-0015) and a Los Gatos Research Enhanced Performance Model CH₄/CO₂/H₂O/NH₃ analyzer (909-00nn).  From the N₂O and CH₄ concentrations, flux densities were calculated using linear regression. Further ongoing work is investigating flux rates in other seasons and identifying contributing factors.