Next to water, nitrogen is essential for crop growth and, as demand for food grows, so too does demand for nitrogen fertilisers. But increased use of nitrogen fertiliser increases the risk of gaseous nitrogen losses such as ammonia (NH3) and nitrous oxide (N2O).
Nitrogen losses from cropping practices that apply both sulfate of ammonia and lime (calcium carbonate) to the ancient, weathered and acidic soils of Western Australia are of particular concern. These nitrogen losses could result in shortfalls in productivity.
To quantify these nitrogen losses, GRDC has invested in research being led by Associate Professor Louise Barton at the University of Western Australia.
“The study has started with a desktop review investigating if the interaction of lime and sulfate of ammonia promote gaseous nitrogen losses. This will be complemented with industry consultation to define the scope of the issue by Dr Fiona Dempster from the University of Western Australia,” Associate Professor Barton says.
The team involved in the research is part of SoilsWest and includes Paul Damon, Associate Professor Matthias Leopold, Professor Zed Rengel (all from the University of Western Australia) and Professor Daniel Murphy from Murdoch University.
Avenues of nitrogen loss
Nitrogen can be lost from cropping systems by several processes. These include nitrogen leaching when water carries applied fertiliser beyond the rooting zone, as well as – importantly – via gaseous pathways such as ammonia volatilisation resulting in ammonia losses, and denitrification, which can result in nitrous oxide and dinitrogen (N2) emissions. Loss of nitrogen fertiliser to the atmosphere via ammonia volatilisation alone may be as high as 30 per cent for WA soils, but data are limited.
“All fertilisers that contain ammonium are susceptible to ammonia volatilisation. The extent of the losses varies depending on fertiliser placement, soil type, soil pH and pH buffering capacity, crop residue management and environmental conditions,” Associate Professor Barton says.
Nitrous oxide and dinitrogen are also produced from nitrogen fertilisers by the actions of microorganisms under particular soil conditions. Denitrification is the reduction of nitrate to dinitrogen with nitrous oxide as an intermediary and occurs in anaerobic parts of the soil when there is sufficient nitrate and carbon available. In contrast, nitrification converts ammonium to nitrate under aerobic conditions and incomplete conversion also results in nitrous oxide emissions.
Applying nitrogen fertilisers enhances microbial activity and therefore production of both nitrous oxide and dinitrogen.
Following the desktop review, detailed glasshouse investigations will be undertaken to get a better handle on nitrogen loss dynamics. The review and industry consultation will direct the nature of these investigations to be conducted by Paul Damon.
They will focus on the effect on crop productivity from surface application of lime and sulfate of ammonia in the short and medium term. The effect of these interactions on growth and yield of canola and wheat will be determined together with measuring key gaseous nitrogen losses.
Outputs from research
“On completion of the research in early 2023, we will provide growers and industry with key findings from the review and glasshouse studies,” Associate Professor Barton says.
We will extend information that explains if applying sulfate of ammonia and lime in close succession is likely to increase gaseous nitrogen fertiliser losses from WA cropping soils and the implications for crop productivity and nitrogen use efficiency.
“We anticipate providing growers and industry with agronomic recommendations for increasing crop productivity and reducing gaseous nitrogen fertiliser losses resulting from our findings.”
More information: Associate Professor Louise Barton, louise.barton@uwa.edu.au