Enteric and simulated pen surface emissions of nitrous oxide from beef cattle feedyards

Nitrous oxide (N₂O) is a greenhouse gas with a global warming potential higher than methane (CH4) or carbon dioxide (CO₂). The objectives of our research were to 1) quantify enteric N₂O emissions from beef cattle, and 2) quantify N₂O emissions from beef feedyard pen surfaces. Live animal enteric emissions were measured using respiration calorimetry chambers. Non-steady state chambers were used to quantify simulated pen-surface emissions. Air-dried feedlot manure was subjected to simulated rainfall (6, 12, 25, or 51 mm), real and artificial urine (6 kg m^-2) or fresh feces (2.4 and 4.8 kg m^-2) at varying temperatures (6°C, 11°C, 21°C, 27°C, 31°C, 38°C, or 46°C) and monitored for 20 to 45 d. In all experiments, gas concentrations were measured with real-time continuous instruments. Mean live animal enteric N₂O emission rates were 10.3 and 19.0 mg N₂O-N animal^-1 d^-1. Cumulative manure N₂O emissions were positively correlated with rainfall. A single N₂O episode was observed following rainfall addition to dry manure between 6°C and 27°C, while two N₂O episodes were observed ≥ 31°C. Cumulative manure N₂O emissions from rainfall on dry manure were positively correlated with temperature, with a step-increase at 31°C. Cumulative N₂O emissions from urine on dry manure were 31% to 70% of emissions from equal mass of water. Cumulative N₂O emissions from cattle feces on dry manure were 8.6% of emissions from equal mass of water. The magnitude of N₂O emissions from feedyards was attributed to the following processes: rainfall > urine >> enteric ≈ feces. Information learned from this research will be useful for developing emission factors, and for selecting best management practices for reducing greenhouse gas emissions from beef cattle feedyards.