Click on “Download PDF” for the PDF version or on the title for the HTML version.

If you are not an ASABE member or if your employer has not arranged for access to the full-text, Click here for options.

Abstract.

Nitrous oxide (N₂O) is a greenhouse gas (GHG) with a global warming potential much greater than that of carbon dioxide (CO₂). Nitrous oxide is emitted from the manure-covered pen surfaces of open-lot beef cattle feedyards, and more than six million beef cattle are fed in the Southern Great Plains. A field research project was conducted to determine the temporal and spatial variability of N₂O emissions from the pen surfaces of a commercial feedyard before and after simulated rainfall. Two week-long monitoring cycles were conducted in April and August 2018 in the Texas Panhandle. Temporal variability was assessed using six continuous automated flux chambers per pen, and spatial variability was assessed using a portable chamber at up to 61 locations in a single pen. Diurnal fluxes varied 5-fold to 10-fold over a 24 h period. Flux varied seasonally, with arithmetic means of 0.56 mg N₂O-N m^-2 h^-1 in April and 3.21 mg N₂O-N m^-2 h^-1 in August. Fluxes measured spatially across the pen surface over a 2 h period at midday were lognormally distributed, with April geometric and arithmetic means of -0.81 and 0.80 mg N₂O-N m^-2 h^-1, respectively, and August geometric and arithmetic means of 0.095 and 2.6 mg N₂O-N m^-2 h^-1, respectively. Fluxes peaked shortly after simulated rainfall. Arithmetic mean N₂O-N flux for the 2 d after rainfall increased over the background level by 4.6-fold in April and 1.7-fold in August. Manure properties measured at the time of flux measurement were poorly correlated with N₂O emissions and were of little value for predicting N₂O emissions, which confirmed that further work is warranted on the biochemistry of feedyard manure. The results of this field research will help refine models for predicting N₂O emissions from open-lot beef cattle feedyards and help to develop effective mitigation methods to conserve feedyard N.