Canola N strategies may need rethink
GroundCover™ Issue: 120 | Author: Sarah Jeffrey
An increased focus on nitrogen (N) in canola could become a catalyst for growers to reap crop productivity improvements worth up to $400 per hectare.
Research being conducted by the GRDC Grower Solution Group Grain Orana Alliance (GOA) into the impact of N applications on canola yield has found significant responses to increased nitrogen rates, but also showed timing of application had little impact on final outcomes.
GOA chief executive officer Maurie Street is encouraging canola growers to reassess their approach to N management and investment to avoid leaving valuable yield “in the paddock”.
He believes yield increases of up to one tonne per hectare are possible if N applications are matched to N requirements, as determined by deep soil testing and nutrient budgets.
“Our trials over the past three years have shown in all but a couple of cases significant yield responses to N applications – in some cases more than 1t/ha,” Mr Street says.
“After running these trials and seeing the response to what would traditionally be considered very high rates of N, it’s now my belief that many growers could be leaving a significant amount of yield in the paddock due to lack of N.
“The trials have been assessing a range of application rates (up to 200 kilograms/ha of N) and timings – at sowing, top-dressing and a split treatment with half the N applied at sowing and half top-dressed.
“Certainly the lower levels of applied N (up to 50kg/ha) are the most profitable, often showing returns better than a 3:1 return on investment.”
Trial results have shown that, in many cases, applications of 100kg/ha of N still offer attractive returns for growers, but in several instances it proved economically viable to apply 200kg/ha of N, which equates to more than 400kg/ha of urea
The 200kg/ha N rate was initially only applied as an experimental treatment with the aim of haying off canola as that is the point where N becomes excessive and starts to depress yields, Mr Street says.
“However, after three years of trial work there hasn’t once been any evidence of yield reduction, which is far beyond expectation.
“This should give growers the confidence to apply liberal rates of N, even very early in the season, without the fear of over-fertilising the crop and running the risk of yield downturns if the season turns poor.
“The question now is whether that fertiliser will be available in the following wheat crop. The current thought is that it will, but GOA had trials in the ground in 2015 to investigate this theory and provide some more solid data to growers.”
The N work comes in the wake of trials conducted between 2010 and 2012 focusing on fine-tuning the addition of sulfur (S) to improve canola performance.
However, after three years, the trials failed to demonstrate any response to the addition of S in yield or oil percentage.
Although not the primary focus of the more recent trials, GOA has continued to include plus and minus S treatment but still has not seen any clear benefits of applying S.
“Traditionally S fertilising in canola was thought to be essential for optimum production and as such N requirements may have been addressed after S and phosphorus (P),” Mr Street says.
“This lack of response to S applications has raised questions over the priority placed on S additions in the GOA region.
“This work has identified often misquoted estimated removal rates of S being double what they really are. It has also highlighted the lack of calibrated soil test critical levels, both of which have impacted the predictability of S responses and may have contributed to an overstatement of potential profitability gains from S applications.”
Mr Street says the findings present a compelling case for some of the expenditure on S to be redirected to N where the response is far more common.
“Current recommendations consider S to be non-negotiable and N applications to be more seasonally dependent,” he says.
“This approach needs to be reversed – S application needs to be more prescriptive in its use and we need to refocus our attention and redirect our expenditure on getting our N rates right because this is where the money is.”
More information:Maurie Street, GOA,
0400 066 201,
Sulfur strategy to improve profitability in canola in the central west of NSW (GRDC Grains Research Updates paper)
GRDC Project Code GOA00001, DAN00129, NGA00003