Comparison of Nitrous Oxide Emissions from Beef Cattle Manure and Soil: Effects of Temperature, Water Content, and Urine Application.

Improved predictive models for nitrous oxide (N₂O) are crucial for assessing the greenhouse gas (GHG) footprint of beef cattle production. Biochemical process-based models to predict GHG from manure rely on information derived from studies on soil and only limited study has been conducted on manure GHG. Little is known about specific factors that drive production and emission of N₂O from feedyard manure. A series of laboratory studies were conducted under controlled laboratory incubations (temperature, water content, urine application) with feedyard manure and soil to evaluate effects of water content, nitrogen (N) concentration, temperature, and other factors on N₂O emission and  N transformations. Results with manure indicated that N₂O was produced rapidly (< 1 h) when urine was applied to dry manure. Flux rates ranged from 200 to 600 mg N₂O m^-2 h^-2, but returned to background levels within 24 h. In contrast, there was a lag in N₂O emissions from soil, where maximum emission from applied urine occurred 7 to 8 d after application. Wet-dry cycling of manure showed small fluxes of N₂O (<100 mg m^-2 h^-1) from manure after rewetting. This work will improve understanding of factors related to N₂O emissions from feedyards and help to parameterize existing process-based models to predict feedyard GHG losses.