Late application of N in wheat struggles to generate economic gain
Author: Sarah Jeffrey | Date: 15 Jun 2015
- Research suggests late foliar nitrogen (N) application to increase wheat protein is unlikely to be an effective management tool in areas where spring rainfall is highly erratic.
- This strategy would only be considered if N in grain recovery levels are consistently increased to more than 50%, untreated protein levels are close to a receival grade threshold and the premium between receival grades is at least $20/t.
- Early applications of N increase the likelihood of attaining both a yield and protein boost.
- Growers should consider top-dressing crops when the opportunity arises rather than waiting for a specific growth stage.
Targeting higher protein grades with late foliar nitrogen (N) applications is unlikely to deliver an economic return to northern wheat growers, according to a detailed three year research project conducted by the Northern Grower Alliance (NGA).
NGA chief executive officer Richard Daniel said a more effective and less risky strategy would be to apply additional N earlier in-crop and provide potential benefits in both protein and yield.
Mr Daniel outlined the findings of the research activity to growers and advisors attending the recent Grains Research and Development Corporation (GRDC) Grains Research Updates in Goondiwindi and Talwood.
“Results from the project suggest that trying to increase wheat protein with late foliar N application is unlikely to be a very effective management tool in areas where spring rainfall is highly erratic,” he said.
“Unless N in grain recovery levels can be consistently increased to more than 50%, grain price differentials of $20 to $40 per tonne are probably necessary before even considering this type of approach.
“Supply of N requirements either prior to or at planting, or as a top up during crop vegetative growth stages would appear a much more reliable and effective strategy to provide both agronomic and economic benefits.
“By putting N on early, there is a good likelihood of getting both a yield as well as a protein boost. However if the application is left to the end of the season, there is little chance of any yield benefit.
“Any economic benefit is reliant on achieving both a significant protein benefit as well as requiring an increase in grain price.”
NGA, a grower solutions group funded by the GRDC, evaluated the impact of late N application on protein levels in wheat across 15 trials during 2012 to 2014.
During 2012 and 2013, 11 trials were conducted using urea at a rate of 40 kg N/ha and evaluated methods of application and application timing. The rate of urea was deliberately high to ensure that protein differences could be reliably measured.
Additional work in 2012 looked at different nitrogen formulations and compared the 40 kg N/ha rate with an application at 20 kg N/ha.
Although significant increases in grain protein were generated when urea solution was applied through a conventional nozzle, no net benefit was recorded at any site during the 2012 and 2013 seasons.
In 2014 the focus shifted to investigating whether a lower rate of N, or multiple low rates of N, could generate improved efficiency of uptake and deliver economic benefits.
Four trials were established in 2014 to evaluate EGA Gregory responses – two in commercial crops near Yallaroi and Mullaley in northern NSW and a further two trials at Tummaville near Millmerran on Queensland’s southern Darling Downs in a `planted small plot’ design.
One of the Tummaville trials was on the site’s existing low N background while the second was on a high N background where 107 kg N/ha was applied prior to planting.
Products used in the trials included Ranger – a 24% N aqueous urea solution - and an experimental urea formulation with added macro and micronutrients.
Three foliar application timings were evaluated - targeting awn peep, early flowering and ~7-10 days after timing two. Single application treatments of 20 or 40kg N/ha were applied together with multiple applications totalling 40 kg N/ha.
“As expected, the late application of nitrogen did not significantly impact on yield in any trial,” Mr Daniel said.
“Additionally, at three of the four sites, there was no significant difference in grain protein level between any treatment and the untreated grain.
“However, at the highest yielding (5.9 t/ha) and lowest protein (9.2%) site, at Mullaley there were significant increases in protein from nearly all treatments.
“The key factors that drove the protein responses at this site were rate of nitrogen and application timing. There wasn’t any measureable benefit from multiple low rate application of N compared to a single application of the equivalent rate.”
The significant increases in protein largely failed to translate into economic benefits though with only six of the 14 treatments improving the receival grade from ASW to APW, according to Mr Daniel.
Unfortunately there was no price difference between ASW and APW grades in 2014 and he said an economic analysis based on a grain price of $267/t, Ranger at $1.80/kg N and application cost of $8/ha/application, found only four treatments had provided a net benefit compared to the untreated, with a range from $9-$33/ha.
“There are some key conclusions that can be drawn from these trials. Firstly, although the late foliar application of N can deliver significant increases in protein, it is unlikely to deliver an economic benefit unless grain N recovery rates are high, untreated protein levels are close to a receival grade threshold and the premium between receival grades is at least $20/t,” he said.
“Secondly, timing differences didn’t prove to be consistent but generally supported application between late head emergence and early milk stages for maximising protein accumulation.
“In terms of application, multiple low rate application in the 2014 trials did not appear to improve the response compared to the same rate applied in one application. However single applications of low rates (20kg N/ha) tended to improve efficiency of grain N recovery and economic benefits compared to single applications of 40kg N/ha.
“Finally, the important take home messages for growers are - apply additional N earlier in-crop to improve yield and protein and top-dress crops when the opportunity arises rather than waiting for a specific growth stage.”
Caption: Chief executive officer of the GRDC-funded grower group Northern Grower Alliance Richard Daniel. Photo supplied by GRDC.
Richard Daniel, CEO, Northern Grower Alliance
07 4639 5344, 0428 657 782
Sarah Jeffrey, Senior Consultant, Cox Inall Communications
08 9864 2034, 0427 189 827
GRDC Project Code NGA00003