A specialist in sustainable farming systems, Dr Peter Grace from the Queensland University of Technology, explained to growers at Grains Week earlier this year the wide consequences of over-use of nitrogen fertiliser. Rebecca Thyer reports
Australian growers could be losing up to $138 million a year through nitrogen being lost to the atmosphere or transported below the root zone - a sizeable hit both in terms of money and its potential to become an environmental liability. Nitrogen leached into groundwater is a health risk, while some of the gaseous nitrogen that escapes from applied fertiliser is one of the more serious greenhouse gases caused by human activity.
[Photo by Brad Collis: Dr Peter Grace at Grains Week: The potential for loss is minimised if a nitrogen management regime is in place]
Dr Peter Grace, Queensland University of Technology"s professor of global change and sustainable systems, says waterlogging induced by poor soil management can release nitrogen applied as fertiliser into the atmosphere.
"The total loss can be in excess of 50 per cent. That"s a significant amount of lost cash through inefficent fertiliser use."
But he says the potential for loss is minimised if a nitrogen management regime is in place. The strategy should consider nitrogen supply and demand and ensure that overfertilisation at any one time does not occur.
He explains that if 550,000 tonnes of nitrogen is applied in Australia annually at a cost of $500 a tonne, and an assumed amount of 20 to 50 per cent is lost as gaseous nitrogen, then growers could be losing between $55 million and $138 million each year. The two greenhouse gases are closely linked to carbon, nitrogen and water cycles.
"Growers can minimise carbon dioxide emissions by using no-till systems, which also improve soil structure and fertility. And they can improve water and nitrogen use to reduce nitrous oxide emissions," says Dr Grace.
Nitrous oxide has a warming potential 300 times that of carbon dioxide. It is released from the decomposition of organic and inorganic nitrogen sources.
Since 1990, greenhouse gas emissions from Australian soils have increased by 29 per cent, including a 130 per cent increase in nitrous oxide emissions predominately from fertiliser application.
"Greenhouse gases are obviously a critical issue in climate change and we can contribute positively to reducing them by using sustainable agricultural practices," he says. "That entails maximising resourceuse efficiency and minimising losses."
While Dr Grace admits that environmental change has to be in balance with production and economic goals, the basics of resource-use efficiency can create win/win situations. "The grains industry can reduce emissions and at the same time maximise the use of resources."
Carbon sequestration - the process of storing carbon in soils - could also add value to cropping. "Carbon trading platforms do exist in the US and the potential exists for it to be expanded into cropping systems," he says.
Dr Grace has completed a scoping study for the International Energy Agency assessing various regions of the world, including south-eastern Australia, for their potential in terms of sequestering carbon in the soil.
He has also developed "Socrates" - a soil carbon calculator for southern Australia - which is currently being updated.
For more information: Dr Peter Grace, 07 3864 2610, firstname.lastname@example.org
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