Nitrous Oxide Emissions from an Open-Lot Beef Cattle Feedyard in Texas

Nitrous oxide (N2O) is a greenhouse gas (GHG) with a global warming potential much greater than carbon dioxide (CO2). Nitrous oxide is emitted from the manure-covered pen surface of open-lot beef cattle feedyards, and there are more than six million beef cattle fed in the Southern Great Plains region. A field research project was conducted to determine the temporal and spatial variability in N2O emissions from the pen surfaces of a commercial feedyard 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- to 10-fold over a 24 h period. Flux varied seasonally, with an arithmetic mean of 0.56 mg N2O (as N) per square meter per hour in April and 3.21 mg N2O (as N) per square meter per hour in August. Fluxes measured spatially across the pen surface over a 2 h period in midday were lognormally distributed, with geometric means of -0.81 mg N2O (as N) per square meter per hour in April and 0.095 mg N2O (as N) per square meter per hour in August. Fluxes peaked shortly after simulated rainfall. Arithmetic mean N2O flux for the 2 d after rainfall increased over background 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 on the biochemistry of feedyard manure is warranted. 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.