Spotlight on soil carbon and nitrogen fertiliser

Photo of a field and cloudy sky

Automated gas chambers measuring nitrous oxide emissions from canola planted on soils with high and low carbon content at the Liebe Group’s soil biology trial site in 2012. This year the chambers will measure emissions in a barley crop.

New research into the effects of increased soil organic carbon levels on nitrogen fertiliser needs and nitrous oxide emissions is planned at Buntine over the next two years.

For the past decade, growers in the Liebe Group have been examining how soil biology and changes in organic soil carbon affect crop yields, grain quality and the health of sandy soil types.

Since 2003, the Liebe Group has recorded an average yield increase of 0.3 tonnes per hectare – or 12 per cent – for crops grown where soil organic carbon has been built up.

Researchers are now interested in learning whether increased soil carbon levels alter nitrogen fertiliser requirements for crops, and if the risk of higher nitrous oxide emissions from crop production increases. 

Lifting soil carbon is promoted as a way to help offset greenhouse gas emissions from grain production. 

The research is said to the first of its kind in Western Australia, and some of the first on sandy soils in Australia.

Dr Louise Barton from the University of Western Australia’s Soil Biology Group and Institute of Agriculture is leading the project, which is funded by the Australian Government’s ‘Filling the Research Gap’ project (as part of its Carbon Farming Futures program) in partnership with the GRDC, the Department of Agriculture and Food, WA (DAFWA), and the Liebe Group.

Dr Barton says it is essential to minimise nitrous oxide emissions (a potent greenhouse gas) from agricultural soils and prevent the loss of nitrogen that would otherwise be available to crops.

She says understanding the relationships between soil carbon levels, emissions and nitrogen fertiliser requirements is critical to:

  • better meet crop nutrient needs;
  • optimise fertiliser use efficiency;
  • reduce the risk of nitrogen leaching; and 
  • lower the potential for higher nitrous oxide emissions.

Last year at the Liebe Group’s long-term soil biology trial site, Dr Barton’s team established an automated gas chamber system  to measure nitrous oxide emissions from high and low-carbon-content soils. These soils are set to be cropped continuously until 2014.

This trial is recording emissions from a commercial rotation of canola, barley and lupins.

It also involves yield assessments for nitrogen rates of 0 and 100 kilograms of nitrogen per hectare for canola and barley.

This season, a separate trial at the same site aims to explore barley yield responses to nitrogen fertiliser (urea) applied at rates of 0, 25, 50, 75 and 100kgN/ha on soils with low and high carbon content.

“In the first instance, we want to assess whether increasing soil carbon will make a difference to the amount of nitrogen required to produce a barley crop,” Dr Barton says.

“Then we will look at the yield response to various nitrogen rates and try to calculate an optimum rate for that year at that site.”

Trial results will be compared with data from other sites in the WA grainbelt and will be fed into the GRDC’s More Profit from Crop Nutrition Initiative.

This initiative is evaluating nitrogen fertiliser responses for a range of crops and soil types where information is lacking.

It aims to equip growers across all grain regions with knowledge and strategies to reduce overall nitrogen use and increase fertiliser use efficiency.

This includes making nitrogen management decision-support tools, such as Yield Prophet®, more robust.

More information:

Dr Louise Barton
08 6488 2543, louise.barton@uwa.edu.au

GRDC Carbon Farming Fact Sheet

Next: Soil health measures to fight acidity on Buntine farm
Previous: Multi-pronged attack against resistant radish

GRDC Project Code UWA00156

Region West