Improved nitrogen efficiency across biophysical regions of the Eyre Peninsula

Improved nitrogen efficiency across biophysical regions of the Eyre Peninsula

Project Manager
Brian Dzoma
Funding Source
DAFF Carbon Farming Initiative
Start Date
15 June 2012
Finish Date
30 June 2015

Summary

This project measured nitrous oxide (N2O) emission levels from wheat grown in rotation with canola, pulses and legume pastures in key biophysical regions of the Eyre Peninsula (EP); while assessing best management practices that local farmers can adopt to minimize N2O losses from the use of synthetic fertilizers through the use of cost effective alternative nitrogen (N) sources.

Nitrous oxide (N2O) is a greenhouse gas (GHG) which lasts in the atmosphere for 121 years and has a global warming potential (GWP) 265 times that of carbon dioxide over a 100 year timescale (IPCC, 2014). Agriculture accounts for approximately 80% of Australia’s nitrous oxide emissions (Dalal et al., 2003) This is primarily a result of using nitrogen-based fertilisers on crops and pastures, and the mineralisation of soil organic matter, both leading to the accumulation of soil nitrate (NO3–) an important ingredient in N2O production. The N2O losses represent a loss of N from cropping soils which can reduce farmer profits and contribute to increasing GHG emissions and global warming and ozone depletion.

Key findings:

  • N2O fluxes were higher at Wanilla (lower EP) than at Minnipa Agricultural Centre (MAC), upper EP, and at both sites the emissions were higher over a 2 year canola wheat rotation than a legume wheat rotation.
  • Results show that there was a response of N2O emissions to the nitrogen applied post sowing, in the canola phase of the 2-year rotation.
  • High pre-seeding soil mineral N resulted in peak N2O fluxes at both sites following a significant summer (2014) rainfall event.

The N2O emission data from both sites show that emission levels in low rainfall farming systems appear to be lower than levels in medium-high rainfall farming systems, and this is consistent with other studies done in dryland low-medium cropping systems (Barton et al, 2008; Officer et al, 2015; Schwenke et al, 2015). One of the objectives of this project was to confirm or oppose current perceptions that farming systems produce low N2O emission from EP soils (Grace pers. comm.), then use that knowledge to develop principles that can be considered in managing N2O losses in low-medium rainfall farming systems.

Wheat yields following canola, a pulse and legume pasture were not significantly different (P<0.05) and ranged from 2.6 – 2.9t/ha at the low rainfall MAC site, but higher (P<0.05) following lupins (2.9t/ha) than following canola (2.7t/ha) at Wanilla (highest N2O flux site). Integrating a legume into cropping systems on the EP did not compromise wheat yields, reducing synthetic N requirements and ultimately reducing N2O emissions.

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