Northern region grain growers should focus on rate when it comes to planning their nitrogen (N) fertiliser strategies to optimise yield rather than application method or timing.
This is one of the key messages from a series of 15 trials conducted over three years as part of a research investment project by the Grains Research and Development Corporation (GRDC) and the Northern Grower Alliance (NGA), which consistently demonstrated that the rate of fertiliser N applied was the main factor impacting yield, grain quality and on-farm returns.
NGA has been heavily involved in projects focussing on N application strategies in wheat with the initial aim of assisting the management of high yielding, and frequently lower protein achieving, varieties such as EGA Gregory or Suntop .
Impact of different nitrogen application methods
One aspect of this research compared the different impacts of nitrogen application.
In Queensland and NSW, growers typically apply nitrogen fertilisers such as urea directly into the soil (banding) or broadcast it on the surface then incorporate.
This is done to reduce the potential for ammonium containing (e.g. sulfate of ammonia) or ammonium producing (e.g. urea) fertilisers volatilising into the atmosphere as the gas ammonia. Volatilisation is one of the pathways of N loss from fertiliser applied or soil N, whereby ammonia gas is produced and lost to the atmosphere.
The results from the NGA trials supported the volatilisation work done by New South Wales Department of Primary Industries (NSW DPI) senior research scientist Dr Graeme Schwenke, which indicated that the volatilisation losses from surface applied urea were frequently much lower than previously expected.
NGA chief executive Richard Daniel said the trial work consistently showed equivalent crop responses in terms of biomass, yield and grain quality from urea spread immediately post sowing, and with no physical incorporation, compared to the same rate of urea spread and incorporated by sowing.
“All sites were nitrogen responsive, with significant grain protein responses to nitrogen rate in all trials,” he said.
“Across 22 comparisons of equivalent N application rates, the crop response has been the same regardless of whether we incorporated the urea at sowing or simply surface spread immediately after sowing.
“Conditions for incorporation by rainfall have varied at every site but in at least six applications, the first recorded rainfall was not until two weeks after spreading.
“In 2015 and 2016 we also evaluated urea incorporated versus surface spread when applied during the fallow period. Again, despite clear N rate responses, there was no significant difference in crop response between incorporated versus spread.
“That is not to say we aren’t losing ‘a quantity’ of N via volatilisation when urea is simply surface spread. It is however indicating that the levels of loss have been low and were not sufficient to measure any difference in crop performance at any of the sites over the past three seasons.”
Mr Daniel said Dr Schwenke’s research indicated that volatilisation loss of N from urea applied by spreading in fallow or in crop ranged from approximately 5 to 15 per cent, indicating N loss by this pathway was not as high as previously considered.
The NGA trial work validated these results under a wide range of commercial conditions and importantly to measured the impact in actual crop yield and grain quality.
“Our trials have shown equivalent wheat yield and protein regardless of whether the urea was mechanically incorporated or simply left on the soil surface,” Mr Daniel said.
“We are not saying there is no loss of N via volatilisation. The field data is simply showing that the losses have been low enough that we couldn’t measure differences in crop yield or protein content.”
Timing of nitrogen application
Image of Richard Daniel kneeling in a wheat cropA range of N application timings were also evaluated as part of the research. A split application of N (50 per cent incorporated at sowing and 50 per cent spread at approximately GS30) was evaluated in all trials, while early and late fallow applications were included in 2015 and 2016.
Split applications of N performed more consistently than expected and provided equivalent crop responses to the same total quantity of N applied at sowing.
In trials where differences were evident, Mr Daniel said the impact appeared to be linked to other agronomic issues such as seedbed soil moisture disturbance (negat...
Read "Prime" Ag News full story!
Be a "Prime" Monthly Member