Diurnal Variability in Nitrous Oxide Flux from Simulated Open-Lot Beef Cattle Feedyard Pen SurfacesConference Paper
Diurnal fluctuations in nitrous oxide as nitrogen (N2O-N) flux have been documented in soils and manures. Researchers often choose to measure N2O-N flux once daily (during a specific time period) to approximate an average daily flux and account for diurnal variation. There has been little effort to quantify these diurnal variation affects at beef cattle feedyards so that they can be incorporated into daily emissions estimates. Fluxes of N2O-N were monitored from air-dried beef cattle manure (water content = 10.8%) over 24 h periods at five simulated rainfall amounts (0 to 50 mm). In summertime conditions (mean T = 28 C), diurnal patterns were observed both before and after water addition, with maximum flux about 2000 h and minimum flux at 0800 h. Following rainfall addition to dry manure, the amplitude (A) of the diurnal variation (calculated as (maximum-minimum)/2) ranged from 0.32 to 0.91 on day 3, and 0.56 to 5.1 on day 16. There was a 1.4 to 4.1-fold difference (max/min) in N2O-N flux over a 24 h period. The max/min decreased with increasing rainfall application. The flux of N2O-N was positively correlated with manure temperature (R2=0.60-0.92), but slopes varied considerably with amount of water and time since water application. These results demonstrate the importance of accounting for diurnal variability when designing experiments to quantify N2O-N emissions at beef cattle feedyards, and also suggest that simple point-in-time sampling and/or temperature-based corrections will likely be difficult when quantifying daily N2O emissions from open-lot beef cattle feedyards.