Trials assess N application timing
GroundCover™ Issue: 112 | Author: Alistair Lawson
A GRDC-funded project looking at late nitrogen applications has highlighted nitrogen management and its effects on wheat yield and protein levels.
The project led by Southern Farming Systems (SFS) and Rob Norton, regional director of the International Plant Nutrition Institute, was one of the GRDC’s Regional Cropping Solutions Networks (RCSNs) – ‘Fast Track’ projects.
SFS chief executive officer Jon Midwood says the idea came from a meeting with the GRDC’s High-Rainfall Zone RCSN in August 2013.
“The yield potential of crops at the time was looking good,” Mr Midwood says. “We had a dry summer and a good winter with minimal waterlogging and the forecast from that point of the season – which was normally quite reliable – was looking positive.”
Mr Midwood says that historically, grain protein levels at delivery have been a good indicator of how tough or otherwise a season has been.
“If you look at grain receivals in 2012, the protein in wheat and barley was low and that was a good indicator of the season. My concern was whether people were missing out on maximising yield and protein in a good season,” he says.
“The general rule of thumb is that if protein is below 11 per cent then it can be assumed that yield is also sub-optimal given the growing season, which means some yield potential could have been missed. Unfortunately, knowing your grain protein only allows you to look back, rather than being proactive during the season.”
On-farm trials were set up at Temora, New South Wales, Conmurra and Wolseley in South Australia, at two sites in Tasmania’s Midlands and three in Victoria’s Western District.
The crops were all wheat and about half were the variety SQP Revenue. The research project kicked in at second node (GS32), or soon after flag leaf emergence (GS39).
Nitrogen was applied at second node, flag leaf emergence, at ear 50 per cent emerged (GS55) and grain fill (GS70). The only restriction was the site at Temora, where GS32 was missed and no nitrogen was applied at that stage.
As part of the project, SFS also took the opportunity to compare solid and liquid fertiliser, with a focus on granular urea, liquid urea and liquid urea-ammonium nitrate (UAN).
The fertiliser was applied at two different rates – one at 25 kilograms per hectare and another at 50kg/ha.
The overall mean response across the trial sites was a yield increase of 0.29 tonnes/ha and a protein increase of 0.5 per cent.
“Some of the sites we trialled already had adequate nitrogen because of high residual levels, or the grower had applied more nitrogen prior to GS32,” Mr Midwood says.
Interestingly, he also notes that while different locations responded to different forms of nitrogen, this did not ultimately make a difference to actual grain yield: “What did make a difference was the timing of the application. Applications at GS39 had the biggest impact on yield, GS55 had the biggest impact on protein and GS70 was too late to have any meaningful effect.”
The rate of fertiliser applied (25kg/ha or 50kg/ha) depended on the background levels of nitrogen which were determined using a deep-soil nitrogen test.
“At sites with a low deep-soil nitrogen test result, 50kg/ha had the best result. Sites with good fertiliser history performed best at 25kg/ha. The best protein results generally came from nitrogen application at GS55,” Mr Midwood says.
He says the results show the value of recording protein levels even if the cereals were to be retained on-farm for feed because it is still a good indicator for the crop’s nitrogen management. It set up the following season’s crop for an appropriate nitrogen plan relative to this protein guide.
Mr Midwood says the results from the project had to be interpreted with the 2013 season in mind, which had a “soft finish”. A tighter (drier) spring finish could limit plant uptake of late nitrogen.
He says it is a case of “one size does not fit all” when it comes to nitrogen application and being responsive to seasonal conditions.
“So in a good season, growers need to be responsive. The last thing you want after a good season is to think you might have left yield or protein in the paddock."
And while there were no significant differences between liquid and granular urea and liquid UAN, Mr Midwood says this might differ in drier finishes.
“In terms of comparing liquid nitrogen and urea, there are a number of factors to consider; the first being that granular urea is the cheapest form of nitrogen.”
However, nitrogen losses from granular urea through volatilisation could be higher when compared with liquid nitrogen fertiliser.
“Also spreading widths are getting wider and there may be a case for considering liquid fertilisers because they can be applied through a boom-spray at the correct width, compared to a spinning disc spreader which can be limited by wind conditions and machine set-up,” Mr Midwood says.
More information:Jon Midwood, Southern Farming Systems,
GRDC Project Code SFS00025
Region South, North