How Do Temperature and Rainfall Affect Nitrous Oxide Emissions from Open-Lot Beef Cattle Feedyard Pens?

Abstract

Abstract. Temperature is a primary factor affecting greenhouse gas (GHG) emissions from agricultural soils, but little is known about how temperature affects nitrous oxide (N2O) emissions from manure. The majority of grain-fed cattle in the Texas Panhandle are finished in large, earthen-surfaced, open-lot feedyards. Manure accumulates in feedyard pens and creates an environment high in nitrogen (N) and carbon (C) that can lead to N2O losses. In previous studies, N2O-N emissions from feedyard manure have been highly variable, ranging from negligible amounts from dry manure to 200 mg m-2 h-1 after a simulated rainfall event. The objective of this research was to determine how temperature affects N2O emissions from feedyard manure following rainfall. A recirculating flow-through, non-steady-state (RFT-NSS) chamber system with 1 m2 pans was used to monitor N2O emissions from beef cattle manure following a single 25.4 mm simulated rainfall event. Emissions were monitored at manure temperatures of 5.0°C, 11.2°C, 17.2°C, 21.5°C, 26.8°C, 31.0°C, 38.1°C, and 46.2°C. At all temperatures, a single N2O episode was observed following rainfall, peaking 2 to 11 h after rainfall with duration of 2 to 3 d. A second N2O episode was observed at temperatures =31.0°C, peaking 3 to 4 d after rainfall with duration of 18 d. When present, the second N2O episode accounted for 72% to 83% of the 20 d cumulative emissions. A step-increase in cumulative N2O emissions was observed between 26.8°C and 31.0°C, believed to be due to a major shift from denitrification to nitrification as the primary process of N2O production. Empirical regression models were developed for predicting cumulative N2O emissions based on temperature, which showed 88% agreement between predicted and field-observed N2O-N flux rates. These regression models will be useful for further quantification of N2O emissions from open-lot beef cattle feedyards in the U.S. Southern High Plains and for assessment of practices for reducing GHG emissions. Keywords: Beef cattle, Chamber, Greenhouse gas, Manure, Nitrous oxide, Precipitation.