Canola School: Assessing nitrogen following a drought and late application timing


Drought is never welcomed by any producer; however, if and when it does happen, residual nitrogen following a dry year could be a small silver lining in an otherwise undesirable situation.

On this Canola School episode, Warren Ward, agronomy specialist with the Canola Council of Canada, walks us through what that nitrogen bonus looks like and also at what point is it too late to add nitrogen to canola crops. Plus, he discusses other factors that need to be considered if applying N later in the growing season.

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Ward says although it is highly likely previously drought-stricken land will have leftover nitrogen, there is really only one way to know for sure and that’s through soil testing.

“One of the ways of knowing, or verifying, is soil tests and there was a bit of an uptake last year in terms of soil testing in the fall because I think a lot of people realize, ‘I applied this much nitrogen, but only removed that much in terms of a crop, so where’s the rest of it?’ and a lot of cases, it was still sitting right there in the field,” says Ward.

After assessing how much, if any, nitrogen is left in the soil from the previous crop year, deciding how much and when to top up those levels gets thrown in the decision making pool.

In years where input prices are higher than producers would like to see, stretching N might be tempting. Knowing where the cut off point is for nitrogen to be truly beneficial to the plant can help navigate these waters and ensure growers aren’t wasting product.

“What you want to look at is kind of up to that six-leaf stages is kind of the the deadline to get your nitrogen on for canola,” says Ward. “If you are doing that topdressing application, you do want to make sure it happens prior to that six-leaf stage because that nitrogen you apply has to move into the soil where the roots can then take it up by the time that the plant needs to do so… that’s the peak nitrogen uptake timeframe for that plant.”

If growers are applying nitrogen just prior to the six leaf stage, trampling may be cause for concern and rightfully so. However, Ward says growers have to decide if the risk outweighs the reward of the extra added nitrogen and the answer could vary from farm to farm and from field to field.

Liquid applications with a streamer or nozzle can cause some leaf burn, but that burn doesn’t usually do much yield damage, unlike shorting the crop N which does curb yield substantially.

He adds that any time fertilizer is broadcast, like with urea for instance, growers should look at using an enhanced efficiency product with it, as a urease inhibitor will help keep the nitrogen from volatilizing and gassing off.

To view all of the Canola School episodes, click here.

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Canola School (view all)Season 14 (2022) Episode 16

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