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Spatial variability of nitrous oxide emission from an irrigated dairy pasture system

Debra Turner1, Deli Chen1, Yong Li1, Robert B. Edis1 and Kevin Kelly2

1The Institute of Land and Food Resources, The University of Melbourne and The CRC for Greenhouse Accounting, Vic 3010, Australia. Email:
Kyabram Dairy Research Institute, Victorian Department of Primary Industries, Kyabram, Vic 3620, Australia.


Nitrous oxide (N2O) is a greenhouse gas, with a global warming potential 300 times that of carbon dioxide (CO2). Agriculture is responsible for 25-35% of Australia’s greenhouse gas emissions and the Australian Greenhouse Office estimates that N2O contributes ~17.5% of agricultural emissions. There is large uncertainty in these estimates because there are few measurements from Australia and emission rates vary in space and time. N2O emissions are thus poorly quantified and there is insufficient information for development of management options to reduce these emissions.

N2O is produced primarily through denitrification, and to a lesser extent during nitrification. N2O emissions are dependent on many factors, but especially on soil moisture content, labile soil carbon (C) supply and substrate availability. Large emissions typically occur after rain or irrigation events in systems with high nitrogen (N) and C availability, and are attributed to denitrification occurring under anaerobic conditions in wet soil.

To characterise the spatial variability and further understand the mechanisms contributing to emissions, 100 mini chambers were placed over a 100 m 2 area of irrigated dairy pasture at the Kyabram Dairy Centre, DPI Victoria, and the head space was sampled for N2O. Soil properties (soil moisture, pH, mineral N, total N and C) under each chamber were be measured, and N2O fluxes analysed geostatistically to discern spatial patterns. The experiment was conducted twice, soon after two separate events of urea application with follow-up irrigation. Average N2O fluxes from the chambers will be compared with fluxes calculated by micrometeorological techniques at the site.

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