Temporal Nitrous Oxide Emissions from Beef Cattle Feedlot Manure after a Simulated Rainfall Event

Nitrous oxide (N₂O) is a greenhouse gas (GHG) emitted from agricultural operations. The objective of this research was to quantify N₂O‐N emissions from simulated open‐lot beef cattle feedlot pens after rainfall. A recirculating‐flow‐through, non‐steady state chamber system consisting of five 1‐m² steel pans was designed for quantifying emissions. A lid was placed sequentially on each pan, and headspace air was recirculated between the pan and a real‐time N₂O analyzer, measuring concentrations every 1 s. Air‐dried manure (89.2% dry matter) from a commercial feedlot in the Texas Panhandle was placed in the pans and then 0, 6.3, 12.7, 25.4, or 50.8 mm of water was applied to simulate a one‐time rainfall event. Emissions of N₂O‐N were monitored for 45 d, where two distinct episodes of N₂O‐N production were observed over time. The first N₂O‐N episode had a duration of 10 h and peaked 2 h after rainfall at a flux of 1.0 to 200 mg m⁻² h⁻¹. The second episode had a duration of 40 d and peaked 15 d after rainfall at a flux of 0.06 to 35 mg m⁻² h⁻¹. The second episode accounted for 69 to 91% of the cumulative N₂O‐N emitted over the 45‐d period. Each millimeter of rainfall increased cumulative N₂O‐N emitted by 167.9 mg m⁻² (r² = 0.99, P < 0.001). This rainfall vs. cumulative emissions relationship will be useful for modeling annual N₂O‐N emissions from open‐lot beef cattle feedlots, and for assessing the effectiveness of best management practices for reducing feedlot GHG emissions. CORE IDEAS: A rapid (60 s) method was developed to quantify fluxes of N₂O‐N from manure. In a 45‐d period, there were two distinct N₂O‐N episodes after simulated rainfall. The first N₂O‐N episode peaked 2 h after rainfall, the second 15 d later. The second accounted for ∼80% of total N₂O‐N emitted during the 45‐d period. Each millimeter of rainfall increased N₂O‐N emissions by 168 mg m⁻² over 45 d.