Kenneth D. Casey, Texas Agrilife Research-Amarillo, Amarillo, TX, Heidi M. Waldrip, Conservation and Production Research Laboratory, USDA-ARS, Bushland, TX, Richard W. Todd, Conservation and Production Research Laboratory, USDA-ARS, Amarillo, TX and N. Andy Cole, Retired, USDA-ARS, Bushland, TX
Accurate estimation of greenhouse gas emissions, from open beef cattle feedlots is an increasing concern. Research measuring GHG fluxes from feedlots, however, has been very limited. Scientists have long used various chamber based techniques, particularly non-flow-through - non-steady-state (NFT-NSS) chambers for measuring soil fluxes. Adaptation of this technique to feedyards presents a series of challenges, including spatial variability, presence of animals, chamber base installation issues, gas sample collection and storage, concentration analysis range, and flux calculations. Various techniques for sealing the chamber to the manure surface including piling soil/manure around the chamber and various weighted skirts were trialed, however no technique was as good at sealing the chamber as a metal ring driven 50-75 mm into the underlying substrate. Animals in the pen could potentially be injured by the chamber bases and/or disturb the measurement installation, so measurements were only conducted in recently vacated pens. The bases must be installed at least 24 and preferably 48 hours before measurements are commenced as the disturbance caused when installing the bases will result in a temporarily enhanced emission flux. Gas samples are immediately injected into a 12 ml evacuated exetainer vial for transport, storage and analysis. Trials of alternative vials led to sample loss and contamination issues. Ten, 20 cm dia chambers are deployed in a pen and yield a reasonable approximation of the average emission fluxes from the pen. The range of gas concentrations after a 30 minute deployment was up to 100 times greater than that typically measured in cropping systems research. This required careful choice of calibration gas concentrations. The ECD detector response may not be linear.