Gaseous nitrogen emissions from Australian cattle feedlots
At any one time, close to 700,000 beef cattle are raised intensively in Australian feedlots. This chapter describes measurements of emissions of the greenhouse gas N2O and the reactive nitrogen gases NH3 and NOx from two Australian beef cattle feedlots made over two years with open- and closed-path concentration measurement systems and backward Lagrangian stochastic dispersion modelling. Emissions of all three gases exhibited marked diurnal cycles with maxima close to mid-day and minima over night. The average emission rate for N2O was 1.3 ± 1.65 (s.d) kg N ha−1 d−1, that for NH3 was 95 ± 36 kg N ha−1 d−1, and for NOx 1.20 ± 0.58 kg N ha−1 d−1. Extrapolating these figures to all the feedlots in the country and accepting the estimate by Mosier et al. (1998) that 1 % of the NH3 and NOx would be converted to N2O after eventual deposition, the direct emissions of N2O from feedlots amount to 241 kt CO2-e year−1 and those from NH3 plus NOx to 181 kt CO2-e year−1, or 43 % of the total N2O emissions. These direct and indirect emissions are substantial, amounting to 60 % in terms of CO2-e of the CH4 emissions measured in the project.
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