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

Nitrous oxide (N 2 O) is a greenhouse gas (GHG) emitted from agricultural operations. The objective of this research was to quantify N 2 O‐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‐m 2 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 N 2 O 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 N 2 O‐N were monitored for 45 d, where two distinct episodes of N 2 O‐N production were observed over time. The first N 2 O‐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 N 2 O‐N emitted over the 45‐d period. Each millimeter of rainfall increased cumulative N 2 O‐N emitted by 167.9 mg m −2 ( r 2 = 0.99, P < 0.001). This rainfall vs. cumulative emissions relationship will be useful for modeling annual N 2 O‐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 N 2 O‐N from manure. In a 45‐d period, there were two distinct N 2 O‐N episodes after simulated rainfall. The first N 2 O‐N episode peaked 2 h after rainfall, the second 15 d later. The second accounted for ∼80% of total N 2 O‐N emitted during the 45‐d period. Each millimeter of rainfall increased N 2 O‐N emissions by 168 mg m −2 over 45 d.