Measuring Methane Emissions From Livestock Operations Using Open-Path Eddy Covariance.

Methane emissions from cattle feedlots in the High-Plains of the United States could represent a large component of agriculture's greenhouse gas inventory.   An eddy covariance system was used to quantify pen-scale CH₄ fluxes from a commercial beef feedlot near Greeley, Colorado.   A  LI-7700 open‑path CH₄ analyzer (Li-Cor Biosciences, Lincoln, NE, USA) was co-deployed with a sonic anemometer and open path CO2/H2O analyzer on a 10-m tower. Livestock weight, feed consumption, and pen surface conditions also were monitored in pens within the sampling footprint of the tower.  The performance of the LI-7700 CH₄ instrument was strongly affected by dust on the lower mirror and a custom air-jet system was developed to improve performance. Large temporal-spatial variations in CH₄ fluxes were apparent which required higher measurement heights and larger footprints. Methane fluxes from the cattle pens were compared to existing CH₄ emissions models for beef cattle.