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Timing Is Everything When Applying Nitrogen On Winter Wheat

A split N application in late fall, which is often desirable in Saskatchewan and Manitoba, where wet conditions can make spring application challenging, does not appear to improve protein levels of winter wheat

Winter wheat provides several rotational benefits — from spreading out the seeding workload to expanding marketing opportunities — but it also creates unique challenges. Winter wheat is a big nitrogen (N) user, however reducing N losses in a fall seeded crop that must overwinter and get on the go early in the spring can be a real nightmare.

So-called enhanced efficiency fertilizer products are designed to curtail N losses through several means, but do these products save more N than they cost? That’s the question a study put on by Agriculture and Agri-Food Canada’s Lethbridge Research Centre is trying to answer. Except that the answer, two years into the three-year study, doesn’t seem to be quite as clear cut as a simple yes or no.

Brian Beres, agronomist with AAFC, leads the study. Test plots are strategically located at Lethbridge and Lacombe, Alta., Scott, Swift Current and Canora, Sask., and Brandon, Man. The aim is to look at winter wheat and its response, in terms of yield and protein content, to different fertilizer forms, placement and timing across different environmental conditions.

The trial is not designed to give a one-size fits all recommendation for fertilizing winter wheat. The purpose is to fine-tune recommendations by soil and growing zone. “We are more interested in what are the parameters that represented each site in terms of precipitation, soil zone and temperature, so those are going to become our fixed effects,” Beres says. “We want to try and establish a relationship between fertilizer management and winter wheat response within soil and environmental parameters, so that we can say this is typically what is going on in black soil zone environments, for example, with respect to this variety and nitrogen management system.”

Two cultivars of winter wheat are being used in the study, a milling variety named Radiant and a soft white general purpose variety, CDC Ptarmigan. All plots have been uniformly seeded using a Conserva Pak or Seed Hawk air drill with nine inch row spacing to insure consistent seed depth and fertilizer placement. The wheat was seeded with a target of 450 seeds per square metre.

The plots were then treated with a combination of different fertilizer treatments. The controls for comparison received zero nitrogen and regular urea. The others were treated with ESN (Environmentally Smart Nitrogen), a polymer coated urea from Agrium; Agrotain, an ammoniacal nitrogen stabilized with a urease inhibitor; and SuperU, a granulated urea with a double bond of a urease inhibitor and increased nitrogen stability with a nitrification inhibitor. The sites at Lethbridge, Scott and Canora also used liquid urea ammonium nitrate (28-0-0 UAN).

Half the fertilizer rate was side-banded at seeding. The timing of the second fertilizer application varied from fall to early, mid and late spring.

FERTILIZING FOR PROTEIN

This is likely the first study of its kind on winter wheat to take into account so many different site and agronomic parameters, which Beres emphasizes is just as important as cultivar selection. “Both cultivar selection and agronomy have to be considered equally and integrated properly to achieve your full yield potential,” says Beres, citing a good example emerging from the study.

One of the experiment components uses just Radiant but with sixteen treatments from a zero nitrogen control to three different types of fertilizer and various placements and timing. The protein range measured across the various treatments was quite dramatic, around 2.5 per cent.

“For protein, 2.5 per cent is quite a bit and if you looked at that you would think there must be different varieties involved or different rates of fertilizer,” says Beres. “In fact it’s a single rate of fertilizer, it’s the same cultivar, but just the fact that we timed the application differently, or we have used a different form, or we’ve placed it all at seeding versus broadcasting it at some point in the fall or spring, we have changed it from quite low, and at times below the minimum standard of 11per cent, to over 12.5 per cent.”

Another result from the study that seems to be fairly clear is that a split application in late fall, which is often desirable in Saskatchewan and Manitoba, where wet conditions can make spring application challenging, does not appear to improve protein levels.

It would appear that the liquid urea is also not proving as effective for increasing yield as some of the other treatments. “The yield is bouncing around a little bit,” says Beres. “The only treatments that are really falling off so far are obviously the control, which doesn’t have any nitrogen, and the liquid UAN, which is unfortunate because one third of the market in Saskatchewan is liquid, but so far we are not seeing it shine like some of the other ones. There is justification for further study with UAN, particularly with stabilizers to see if the efficacy can be improved.”

With one more year of data to collect, it does not appear that Beres and his colleagues are going to have a one-size-fits-all solution for producers, particularly when it comes to the effects they can expect from high cost inputs like enhanced efficiency fertilizers, which underscores the need for sound agronomic research.

“The challenge is that there is not one prescription. Our job as agronomists will be to understand what soil, environment and other factors influenced the response of each system, which will involve some pretty complex data and system stability analyses,” says Beres. “It’s really going to be a matter of predicting in your soil zone, based on the precipitation you anticipate, this is what you could expect from a particular cultivar and nitrogen management system.”

From that information each farmer will, as is so often the case, have to make a decision based on his own situation and the likely economic impact, which goes far beyond just choice of fertilizer and variety to everything from local weather and soil variability to management practices like timing and placement.

Angela Lovell is a freelance writer based at Manitou, Man.

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Angela Lovell

Angela Lovell is a freelance writer based in Manitou, Manitoba. Visit her website at http://alovell.ca or follow her on Twitter @angelalovell10.

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