Greenhouse Gas Emissions from Beef Cattle Feedlot Pen Surfaces in Texas.

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 N₂O and CH₄ flux rates from pen surfaces at two commercial beef cattle feedlots in Texas during 2013. Fluxes from pen surfaces were measured using 219 mm i.d., non-flow-through non-steady-state (NFT-NSS) chambers on 25 sampling days at 12:00 pm (Central Standard Time) during spring and fall, in five 5-d measurement campaigns. Ten chambers were arranged in two rows of five, strategically covering representative areas of the pen, including areas near feedbunks and water troughs. Headspace samples were collected from the chambers at 0, 10, 20 and 30 min using 20 ml polypropylene syringes, transferred to evacuated 12 mL Exetainer vials, and analyzed using a gas chromatograph. From the N₂O and CH₄ concentrations, flux densities were calculated using the Quad method. Nitrous oxide fluxes varied considerably across the pen surface, generally being higher on manure mounds and at the toe slope of manure mounds. Median N₂O fluxes for each 5-d campaign were 0.01, 0.01, 1.38, 1.14 and 0.17 mg N₂O m^-2 h^-1, respectively. Methane fluxes were generally low under the dry conditions experienced during the study but were considerably higher from moist areas and somewhat higher over manure mounds. Median CH₄ fluxes for each 5-d campaign were 0.01, 0.44, 0.14, 0.01, and 0.22 mg CH₄ m^-2 h^-1, respectively. Further ongoing work is investigating flux rates in other seasons and identifying contributing factors.