Accurate estimation of greenhouse gas emissions, including nitrous oxide and methane, from open beef cattle feedlots is an increasing concern given the current and potential future reporting requirements for GHG emissions. Research measuring emission fluxes of GHGs from open beef cattle feedlots, however, has been very limited. Soil and environmental 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.
Following an extensive review of the literature on measuring emissions from cropping and pasture systems, it was decide to adopt non-flow-through - non-steady-state (NFT-NSS) chambers as the preferred measurement methodology. However, the use of these NFT-NSS chambers had to be adapted for use in conditions of beef cattle feedyards and open corral dairies.
Trials of various techniques for sealing the chamber to the manure surface including piling soil/manure around the chamber and various weighted skirts were trial, however no technique was as good at sealing the chamber as a metal ring driven 50-75 mm into the underlying substrate.
Chamber bases could potentially injure animal in the pen and/or animal could disturb the measurement installation, so measurements were only conducted in recently vacated pens.
Gas samples were drawn from a septa in the chamber cap using a 20 ml polyethylene syringe and 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.
Gas samples were analyzed using a gas chromatograph equipped with ECD, FID and TCD detectors for nitrous oxide, methane and carbon dioxide determination, respectively.
The metal rings or 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.
Ten, 20 cm dia chambers constructed from PVC pipe caps are deployed in a pen and yield a reasonable approximation of the average emission fluxes from the pen.
The range of gas concentrations measured in the chamber at the end of a 30 minute deployment was up to 2 orders of magnitude greater than that typically measured in cropping systems research. This required careful choice of calibration gas concentrations and calibration of the gas chromatograph. The response of the ECD detector used for determining N2O concentration may not be linear over the entire range experienced.
The rate of increase in concentration in the chamber is often curvilinear in form and a quadratic approach was adopted for determination of the flux rate.
On-going studies are quantifying N2O and CH4 flux rates from pen surfaces in a cattle feedlots under varying seasonal conditions; further work is identifying contributing factors.
Kenneth D. Casey, Associate Professor at Texas A&M AgriLife Research, Amarillo TX email@example.com
Heidi M. Waldrip, Research Soil Scientist at USDA ARS CPRL, Bushland TX; Richard W. Todd, Research Soil Scientist at USDA ARS CPRL, Bushland TX; and N. Andy Cole, Research Soil Scientist at USDA ARS CPRL, Bushland TX;
For further information, contact Ken Casey, 806-677-5600
Research was partially funded from USDA NIFA Special Research Grants
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