Empirical model of annual nitrous oxide emissions from open-lot beef cattle feedyard pens in the southern high plains

Authors: Parker, David; CORTUS, ERIN - University Of Minnesota; CASEY, KENNETH - Texas A&M Agrilife; Marek, Gary; HEFLIN, KEVIN - Texas A&M Agrilife; Waldrip, Heidi

Submitted to: ASABE Annual International Meeting
Publication Type: Proceedings
Publication Acceptance Date: 8/1/2018
Publication Date: 8/1/2018
Citation: Parker, D.B., Cortus, E.L., Casey, K.D., Marek, G.W., Heflin, K.R., Waldrip, H. 2018. Empirical model of annual nitrous oxide emissions from open-lot beef cattle feedyard pens in the southern high plains [abstract]. ASABE Annual International Meeting. Paper #1800508.

Interpretive Summary: Nitrous oxide is a greenhouse gas that has been linked to climate change. High concentrations of nitrogen and carbon make livestock manure at beef feedyards a source of nitrous oxide emissions. Reported nitrous oxide emissions from beef cattle feedyards have been highly variable. Scientists from USDA-ARS (Bushland, Texas), University of Minnesota (St. Paul, Minnesota), and Texas A and M AgriLife Research (Amarillo, Texas) developed a computer model to help predict and study nitrous oxide emissions from feedyard pen surfaces. Using weather data from 1996 to 2017, they showed that precipitation was responsible for 62 percent of all nitrous oxide emissions, while urine and feces were responsible for 30 and 8 percent, respectively. Emissions during the three warmest months of June, July, and August accounted for more than half of annual emissions. Keeping feedlot pens dry, especially during the hot summer months, will help to reduce nitrous oxide emissions from livestock manure.

Technical Abstract: Nitrous oxide (N2O) is a greenhouse gas with global warming potential about 300 times that of carbon dioxide. More than seven million beef cattle are finished in feedyards in the semiarid Southern High Plains. Precipitation, feces, and urine deposited directly and continuously on the open-lot pen surfaces contribute to N2O emissions. The objective of this research was to estimate daily and annual N2O emissions from open-lot feedyard pens in the Southern High Plains through the use of an empirical model. Regression equations derived from lab experiments were used to estimate N2O emissions in an Excel spreadsheet based on daily precipitation, manure temperature, and urine and feces deposition over the 22 year period from 1996 to 2017. Mean annual precipitation ranged from 136 to 658 mm/yr (mean 367 mm/yr). Mean daily manure temperature ranged from -4.9 to 32.8 degrees C (mean 15.2 degrees C). Urine deposition was estimated at 1.4 mm/d (511 mm/yr) at a cattle density of 15 square meters per animal. Model-simulated daily N2O emissions were best approximated by a lognormal distribution, with range 0.3 to 1,351 mg N2O-N per square meter per day, and mean, geometric mean, and median of 71.1, 34.3, and 38.4 mg N2O-N per square meter per day, respectively. The model-simulated mean (plus/minus SD) per capita feedyard capacity annual N2O emission rate for the 22-yr period was 0.39 (plus/minus 0.07) kg N2O-N per animal per year, with range 0.23 to 0.51 kg N2O-N per animal per year. Emissions due to precipitation, urine deposition, and feces deposition on the pen surface accounted for 61.8, 29.7, and 8.5 percent of overall N2O emissions, respectively. Emissions from June, July, and August accounted for 51.7 percent of annual emissions. The mean model-simulated emission rate for the 22 year period compared favorably to three years of measured N2O emission data from two feedyards in Texas. Model-simulated daily emission rates were 1.3 to 13.1 fold higher than measured from two weeks of daily emission data from feedyards in Nebraska and Texas. The model will continue to be refined to better simulate field-measured N2O emission rates, and a sensitivity analysis will be conducted to assess how variability in regression parameters affects model simulations.