Emissions of the indirect greenhouse gases NH3 and NOx from Australian beef cattle feedlots
O. T. Denmead A B D , D. Chen B , D. W. T. Griffith C , Z. M. Loh B , M. Bai C and T. Naylor CA CSIRO Land and Water, GPO Box 1666, Canberra, ACT 2601, Australia.
B Faculty of Land and Food Resources, University of Melbourne, Vic. 3010, Australia.
C Department of Chemistry, University of Wollongong, NSW 2522, Australia.
D Corresponding author. Email: tom.denmead@csiro.au
Australian Journal of Experimental Agriculture 48(2) 213-218 https://doi.org/10.1071/EA07276
Submitted: 16 August 2007 Accepted: 28 October 2007 Published: 2 January 2008
Abstract
Emissions of indirect greenhouse gases, notably the nitrogen gases ammonia (NH3) and the odd oxides of nitrogen (NOx), play important roles in the greenhouse story. Feedlots are intense, but poorly quantified, sources of atmospheric NH3 and although production of NOx is to be expected in feedlots, rates of NOx emission are virtually unknown. In the atmosphere, these gases are involved in several transformations, but eventually return to the earth in gaseous or liquid form and can then undergo further transformations involving the formation and emission of the direct greenhouse gas nitrous oxide (N2O). The IPCC Phase II guidelines estimate that indirect N2O emissions due to atmospheric deposition of N compounds formed from NH3 and NOx could be ~14% of the direct emissions from agricultural soils or from animal production systems. IPCC recommends that these indirect emissions be accounted for in making inventory estimates of N2O emission. This paper is a preliminary report of emissions of NH3 and NOx from two Australian feedlots determined with micrometeorological techniques. Emissions of nitrogen gases from both feedlots were dominated by emissions of NH3. The average NH3 emission rate over both feedlots in winter was 46 g N/animal.day, while that of NOx was less than 1% of that rate at 0.36 g N/animal.day. It was apparent that NH3 release was governed by the wetness of the surface. Rates of emission from the feedlot with the wetter surface were almost three times those from the other. The IPCC default emission factor for the combined emission of NH3 and NOx from livestock is 0.2 kg N/kg N excreted, but in our work, the emission factor was 0.59 kg N/kg N excreted. Potential emissions of N2O due to NH3 and NOx deposition were estimated to be of the same magnitude as the direct N2O emissions, the sum of direct and potential indirect amounting to ~3 g N2O-N/animal.day. If applied nationally, this would represent a contribution of N2O from Australian feedlots of 533Gg CO2-e or 2.2% of all Australian N2O emissions.
Acknowledgements
We thank the Australian Greenhouse Office and Meat and Livestock Australia for their interest and financial support and the management, and staff of the Victorian and Queensland feedlots for making their sites available and providing much material help.
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