Does increasing soil carbon in sandy soils increase soil nitrous oxide emissions from grain production?

International research demonstrates increasing soil organic carbon benefits crop productivity, but also enhances other greenhouse gas emissions including nitrous oxide and methane.

ACHIEVEMENTS

  • Land management practices that increase soil organic carbon (SOC) in Western Australia’s cropping soils benefit crop production, and have the potential to decrease nitrogen and other fertiliser needs.
  • The greatest risk of N2O emissions from a sandy soil in the Western Australian grain belt occurred in response to summer-autumn rainfall events, and more so with increasing SOC.
  • The proportion of nitrogen fertiliser applied that was lost as nitrous oxide from a sandy soil in the Western Australian grain belt ranged from 0.08 to 0.12%.
  • Nitrogen supply (via mineralisation) prior to seeding varied depending on soil type and summer rainfall, and needs to be included when determining annual nitrogen fertiliser requirements.

OVERVIEW

Increasing soil organic carbon is promoted as a strategy for sequestering carbon dioxide and mitigating anthropogenic greenhouse gas emissions. This 2.5 year field-based study concluded that land management practices that increase soil organic carbon in Western Australia’s sandy cropping soils should be encouraged. Increasing soil organic carbon benefited grain yield and increased plant available nitrogen, and showed potential to decrease nitrogen fertiliser inputs.

Although increasing soil organic carbon increased soil nitrous oxide emissions (and inhibited methane uptake), losses were modest (0.08–0.12% of applied nitrogen fertiliser) and significantly less than the international default value (1.0%). This finding, and past research in south-western Australia, supports lowering Australia’s current emission factor (0.3%) for calculating nitrous oxide losses from the application of nitrogen fertiliser to rainfed cropping soils in Australia’s semi-arid regions.

Growers should also be encouraged to modify nitrogen fertiliser inputs to reflect changes in plant available nitrogen resulting from improvements in soil organic carbon. This will require fertiliser decision support models to accurately predict soil nitrogen supply. Optimising nitrogen fertiliser inputs will increase profitability for growers, plus minimise soil nitrous oxide emissions.

FUNDING

This project was supported by funding from the Australian Government Department of Agriculture and the Grains Research and Development Corporation. In-kind support was provided by the Liebe Group, Department of Agriculture and Food WA, and The University of Western Australia.

CONTACT

Louise Barton

The University of Western Australia

louise.barton@uwa.edu.au

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