Applying the Eddy Covariance Technique to Measure Methane Emissions from a Beef Cattle Feedlot in Kansas.

The eddy covariance technique has been widely used in flux networks around the word to measure gas exchange above plant canopies. The eddy covariance technique may also be an alternative to estimate methane emissions from confined animal feeding operations. However, the eddy covariance technique relies on the assumption that the source strength of the underlying surface is homogeneous, which may not hold true in a feedlot where the surface can have different source strengths depending on animal position and wind direction. The objective of this study was to evaluate the use of the eddy covariance technique in a beef cattle feedlot. The study was carried out in a feedlot in Kansas. The flux and micrometeorological instrumentation was set up at the north edge of the feedlot, and measurements were carried out for 8 months. The wind velocity components were measured using a 3D sonic anemometer (CSAT3, Campbell Sci.) at 10 Hz. Measurements of H₂O, CO₂ and CH₄ mixing rations were performed using a close-path gas analyzer (G2311f) at the same frequency. To evaluate the performance of the close-path analyzer, an open-path analyzer (Li7500, Li-cor, Lincoln, NE) was used to measure CO₂ and H₂O at the same frequency. An automated panoramic camera was set up at the tower to monitor the movement of the cattle in the pans close to the tower. The high frequency data were analyzed using the software eddy pro (Li-cor, Lincoln, NE).  Our results indicate good agreement between open-path and closed path CO₂ measurements. The fluxes values were quite variable and dependent on wind direction and animal position in the feedlot. The flux values obtained are consistent with values found in the literature.