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-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 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) (r(2) = 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.