IN INOCULANTS Nodulaid - 17th International Nitrogen Fixation ...

17 th International Congress on Nitrogen Fixation
Fremantle, Western Australia
27 November – 1 December 2011
Session Details: Thursday 1 December 2011
Concurrent Session 16 – Symbiotic Impacts & Emissions
1100 - 1230
Authors: Graeme Schwenke 1 , Pip Brock 2 & David Herridge 3
1 NSW Department of Primary Industries, Marsden Park Road, Calala, 2340, New South
Wales.
2 NSW Department of Primary Industries, Port Stephens Fisheries Centre, Locked Bag
1, Nelson Bay, 2315, New South Wales.
3 University of New England, Primary Industries Innovation Centre, Armidale, 2351, New
South Wales.
Presentation Title: Nitrogen-fixing legumes in farming systems reduce greenhouse gas emissions
Presentation Time: 1120 – 1140
Nitrous oxide (N2O) is a greenhouse gas with close to 300 times the global warming potential of carbon dioxide
(CO2). A major source of N2O emissions (50–60%) is associated with the application of nitrogenous fertilisers to
agricultural soils. However, the direct emissions of N2O from soil, as a by-product of nitrification and an endproduct
of denitrification, represent only a fraction of total greenhouse gas emissions related to N fertiliser use.
Greenhouse gases (principally CO2) are also emitted in the production, transport and application of nitrogenous
fertilisers and can be quantified using Life Cycle Assessment (LCA). Emissions of greenhouse gases from
agricultural systems may be mitigated through partial substitution of fertiliser nitrogen (N) inputs with biologicallyfixed
legume N because the latter is produced in the soil in situ and is of a dispersed, i.e. non point-source, and
slow-release nature. To compare total greenhouse gas emissions from crop sequences with contrasting inputs of
fertiliser- and legume-N in Australia‟s northern grains region, we monitored N2O emissions from the sequences
for two years and conducted cradle-to-gate, i.e. pre-farm plus on-farm but not post-farm, LCA. We used
automated greenhouse gas (N2O, CO2, CH4) measuring chambers to monitor soil emissions 7-8 times per day.
During two years of measurement, cumulative soil N2O emissions differed fourfold between the rotation
treatments, with canola (+N)–wheat (+N) emitting 1.32 kg N2O-N/ha, compared to 0.71 kg N2O-N/ha from the
chickpea–wheat (+N) treatment and only 0.34 kg N2O-N/ha from the chickpea–wheat (no N) treatment. These
treatment differences were increased further in the LCAs when all emissions associated with fertiliser N were
included. We conclude that substitution of fertiliser N inputs with biologically-fixed legume N can substantially
reduce greenhouse emissions from grain production systems.
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2011