Australia
July 9, 2012
New research funded by the Grains Research and Development Corporation (GRDC) may change the way northern region grain growers approach nitrogen application.
That’s the view of GRDC northern panel chair James Clark, who says the research results presented to growers and advisers at the GRDC Updates earlier this year are challenging long-held views.
“These results may be a game changer for northern grain growers because they usually try and time nitrogen applications with rainfall events to avoid loss of nitrogen into the atmosphere due to volatilisation,” Mr Clark says.
“Further research needs to be done and GRDC is funding another year of trials but it could mean nitrogen can be applied at different times and with different methods than we currently use.
“This has the potential to impact on canopy management practices and could reduce the input costs of growers.”
The trials were carried out by Graeme Schwenke, Adam Perfrement, Bill Manning and Guy McMullen from the NSW Department of Primary Industries (NSW DPI).
Dr Schwenke said the research looked at how much nitrogen was lost when applied to the soil surface in different formulations at different times.
“Fertiliser nitrogen can be lost from the soil surface as ammonia gas via the process of volatilisation,” he said.
“Just how much is lost depends on a range of factors, including soil moisture, temperature, pH, naturally-occurring lime in the soil, ground cover, wind, soil clay percentage, and fertiliser type.”
The results from trials on neutral to alkaline cracking clay soils showed nitrogen volatilisation losses from four top-dressed mid-tillering wheat crops were minor – less than 10 per cent loss over a whole month during winter 2011.
Fertiliser was applied to dry soil, temperatures were low, and there was little rain after application. There were only small differences in losses between fertiliser types.
Two fallow paddocks broadcast with urea or ammonium sulphate in spring also had minor losses, except where ammonium sulphate was spread on a paddock with carbonates at the surface when losses were more than 30pc of that added.
Two grass pasture paddocks broadcast with urea or ammonium sulphate in autumn or spring both had severe losses from urea (23-31pc loss), but only minor loss from the ammonium sulphate.
“Don’t assume all applied fertiliser is lost if rain doesn’t come after topdressing or broadcast spreading,” Dr Schwenke said.
“We recommend growers avoid using ammonium sulphate on paddocks with carbonates in the surface soil.
“Ammonium sulphate is less risky for grass pastures on non-carbonate soils than urea if rainfall doesn’t come soon after.”
Mr Clark welcomes debate on the issue, acknowledging that growers may be averse to changing fertiliser regimes without further evidence.
He says the previous rule of thumb was that up to 30pc of nitrogen could be lost to the atmosphere if it didn’t rain soon after application.
The figure of 10pc loss could mean big savings for growers, he said.
To download the GRDC Update paper, visit www.grdc.com.au/updates
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