29 August 2026, AU: A national multidisciplinary project is gathering data to better understand where and when nitrogen is lost from soils across Australia.
New South Wales trials are part of a national research effort to explore how much nitrogen fertiliser crops use, how much remains in the soil, and how much is lost from the cropping system.
NSW Department of Primary Industries and Regional Development Senior Research Scientist Dr Graeme Schwenke says each location within the national multidisciplinary project has 6 to 8 nitrogen fertiliser rates, with 2 rates receiving the isotope tracer 15N.
“As the tracer behaves like ‘regular’ nitrogen (14N), researchers can quantify how much of the applied fertiliser a crop takes up, how much remains in the soil or residues, and how much is lost to the environment.”
The GRDC-invested research aims to produce more accurate modelling of nitrogen cycling via the Agricultural Production Systems sIMulator (APSIM), the backbone of Yield Prophet. It is also hoped the work will lead to better predictions of nitrogen rate requirements by application location.
At Tamworth, 65% of the urea was applied pre-sowing (broadcast or drilled), with the remaining 35% applied at growth stage 30 (broadcast) (Table 1), whereas at Wagga Wagga all urea was broadcast at the 4-leaf growth stage (Table 2).
Tamworth
At Tamworth in 2023, Dr Schwenke says the results showed that when 150 kg/ha and 200 kg/ha of nitrogen were applied to wheat, dry spring conditions meant that most of the nitrogen taken up by the crop came from the soil, with only a small amount of the 15N-labelled fertiliser used.
“At Tamworth, a reasonable amount of the 15N-labelled fertiliser was found in the wheat grain, a small amount in the crop residues, and a large amount in the soil to a depth of 80 cm.”
Overall, he says, 38 to 45% of 15N-labelled nitrogen was lost from the system, likely during wet conditions post-application and again between harvest and post-season soil sampling.
Table 1: Crop rotation at Tamworth
Tamworth
2023
2024
2025
Cycle 1
Wheat +15N
Barley
Canola
Cycle 2
Chickpeas
Wheat +15N
Canola
Cycle 3
Chickpeas
Barley
Wheat +15N
Source: Graeme Schwenke, NSW DPIRD
Wagga Wagga
At Wagga Wagga in 2023, when 150 kg/ha and 200 kg/ha of nitrogen were applied to wheat, some nitrogen was supplied by the soil, with a larger proportion (relative to the Tamworth data) entering the crop from the 15N-labelled fertiliser.
“At Wagga Wagga, the first year’s results showed that 30 to 45% of 15N-labelled fertiliser was not found in either the plant or the soil after harvest and was therefore presumed to be lost from the farming system.”
Table 2: Crop rotation at Wagga Wagga
Wagga Wagga
2023
2024
2025
Cycle 1
Wheat +15N
Barley
Barley
Cycle 2
Lupins
Wheat +15N
Barley
Cycle 3
Lupins
Barley
Wheat +15N
Source: Graeme Schwenke, NSW DPIRD
Loss pathways
Dr Schwenke says that at Tamworth, nitrogen loss via volatilisation was low, while at Wagga Wagga it was high. Another loss pathway is denitrification (to nitric oxide, nitrous oxide and di-nitrogen). “This was probably high at Tamworth but less so at Wagga Wagga.”
He says that volatilisation losses at Tamworth were 1% in 2023 and nil in 2024. These were measured from pre-plant nitrogen (100 kg/ha).
“At Wagga Wagga, volatilisation losses at the 4-leaf stage (120 kg/ha of nitrogen applied) in 2024 were 14%, and in 2025 were 24%.” Volatilisation losses were not measured in 2023 at Wagga Wagga.
Dr Schwenke says the median volatilisation losses across the wider project’s 7 sites (Western Australia, South Australia, Victoria, NSW and Queensland) were 9%, with a range of 0 to 48% of nitrogen applied. The highest volatilisation losses typically came from:
soils with low cation exchange capacities
soils that were moist or wet when urea was applied
soils where there was little to no rain (less than 5 mm) in the 7 days following urea application
soils where it was windy after spreading.
Nitrogen movement
By December 2024, Dr Schwenke says the second Tamworth crop had taken up another 22% of the original 15N nitrogen applied in 2023 (no new nitrogen was applied in 2024). However, the second crop at Wagga Wagga used only a further 5% of the originally applied nitrogen, with 16% remaining in the soil in December 2024.
After 2 years, he says the studies at Tamworth and Wagga Wagga showed that 30 to 45% of the fertiliser nitrogen applied was not found in grain, crop residue or soil.
At Tamworth:
Denitrification was likely the main nitrogen loss pathway, suggesting a role for a nitrification inhibitor.
Fertiliser nitrogen was stranded in the topsoil by dry in-season conditions, which is a risk when broadcasting.
The unused nitrogen ‘leached’ downwards during the fallow, but much of it was used by the second crop.
After 2 years, 28% of the original 15N fertiliser remained in the soil, with the highest concentration near the surface, likely in organic forms.
At Wagga Wagga:
Volatilisation was the main nitrogen loss pathway, which is a risk when broadcasting. A urease inhibitor should be investigated for this situation.
There was greater first crop nitrogen uptake, but little uptake by the second crop.
After 2 years, 16% of fertiliser nitrogen was still found in the soil as organic matter, with some being mineralised for subsequent crops.
Dr Schwenke says all project data is being used to fine-tune APSIM, with the volatilisation data specifically used to test a new volatilisation module developed by project partners and CSIRO.
“This will allow users of this or Yield Prophet to more confidently predict nitrogen dynamics across the cropping system at various locations and seasonal conditions.”
Research collaborators
Co-investors in GRDC’s ‘Predicting nitrogen cycling and losses in Australian cropping systems – augmenting measurements to enhance modelling’ include the Western Australian Department of Primary Industries and Regional Development, the NSW Department of Primary Industries and Regional Development, the South Australian Research and Development Institute, Queensland Department of Primary Industries, Agriculture Victoria, Murdoch University, the Queensland University of Technology, the University of Queensland, the University of Western Australia and CSIRO.
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