Managing Nitrogen for Ontario Canola

Friday, May 22, 2026

Research is helping fine tune rates, timing & placement to achieve higher canola yields

By Mary Loggan

Nitrogen underpins canola yield, quality and profitability, but it is also one of the most difficult nutrients to manage.

Soil behaviour, weather, timing and placement all influence how much of the fertilizer growers pay for reaches the crop.

Recently, Mario Tenuta, professor and acting head of the Department of Soil Science at the University of Manitoba, shared his latest research with Ontario farmers in a nitrogen in canola webinar co hosted by the Ontario Certified Crop Advisor Association and the Ontario Soil and Crop Improvement Association, underscoring both the opportunities and challenges for local producers.

For Tenuta, the central task is to align nitrogen supply with canola’s potential while managing the risk of loss in winter and spring systems.

In Ontario, that increasingly means tailoring decisions to the high-yielding potential of winter canola, while drawing lessons from Prairie work in spring canola.

Why nitrogen matters

“Nitrogen is the nutrient that most strongly drives canola yield,” Tenuta says.

“Canola produces a large amount of above ground biomass (8,000–13,500 lb/ac), and much of the nitrogen in that biomass is transferred into the oilseed, where a 50 bushel/ac crop can take up a total of 120 lb N/ac.

“That removal is high because canola seed is about one quarter protein, and the meal left after crushing can contain up to 40 per cent protein.”

He says that the production system influences the demand.

“Eastern Canada is dominated by winter canola, where yields can reach 80 bushels/ac or more, compared to roughly 55 bushels/ac for spring canola in Western Canada.

“As a result, winter canola can re-move 200 lb N/ac or more with the oilseed, versus about 120 lb N/ac for spring hybrids.”

Nitrogen is important throughout the season.

“Early on, it supports leaf and canopy development so the crop can capture sunlight efficiently.” Later, it supports branching, flowering, and pod formation, all of which are key to final yield, he explains.

“For winter canola in Ontario, nitrogen is critical for building a strong stand in the fall and then supporting rapid regrowth and biomass accumulation after dormancy.”

Benefits of good management

“When nitrogen is managed well, growers see higher and more consistent yields because the crop has access to nitrogen during critical growth stages such as branching, flowering and pod filling,” Tenuta says.

Better management also improves nitrogen use efficiency, so a greater share of applied fertilizer is taken up by the crop rather than lost to the environment, he notes.

“This maximizes return on fertilizer investment and helps reduce nitrate losses to water and nitrous oxide emissions.”

Tenuta stresses that sulphur must be considered alongside nitrogen.

“I’d be remiss not to mention sulphur. It’s also very important to consider sulphur availability; the crop won’t respond adequately to nitrogen.

“Canola is a high sulphur demand crop with a particularly high need from rosette to bolting.”

Sulphur is important for seed protein and oil and is required for glucosinolate production.

“Sulphur deficiency is easy to spot because, unlike nitrogen deficiency, it is the young leaves that are pale yellow in colour. Leaves may seem to be ‘cupped’ and have purple edges as well.

“Ammonium sulphate (21 0 0 24S) is the most readily available fertilizer form for sulphur. As benchmarks, 30 lb S/ac and 40 lb S/ac are usually good targets of ammonium sulphate for spring and winter canola, respectively.”

He advises that growers should account for the nitrogen in ammonium sulphate, along with soil test results, when determining total fertilizer nitrogen rates.

Why is nitrogen challenging?

“Managing nitrogen is challenging because nitrogen is highly dynamic in soil and is affected strongly by weather conditions,” Tenuta notes.

Nitrogen can be lost through ammonia volatilization, nitrate leaching and denitrification, particularly when soils are wet.

“For winter canola, nitrogen management must consider availability at fall planting and then at spring green up. For spring canola, the availability of nitrogen from planting to rosette is important.”

Applying nitrogen too early can increase the risk of loss under wet conditions, while applying it too late may limit early growth and yield potential.

He says when nitrogen is insufficient, the crop shows reduced canopy growth, fewer branches and pods, smaller seeds and lower yield.

“Nitrogen deficient plants are stunted and spindly with an open canopy.

“Leaves yellow from the margins, and lower leaves can brown and die. Lower leaves of winter canola can appear reddish purple or pinkish.

“A poor canopy captures less sunlight and allows weeds to outcompete the crop, reducing yield and potentially creating weed issues in future years.”

Start with the soil test

For Tenuta, the first step is knowing what is already in the soil.

“The availability of nitrogen in the soil matching that of the canola is key to a good crop.

“Soil testing is the best way to determine how much nitrogen is present for the crop to use.

“In Eastern Canada, including Ontario, nitrogen planning for winter canola is more complex because the crop must survive winter and then achieve high yields.”

Tenuta explains that fall sampling to one foot is useful to gauge levels needed for establishment, as a six leaf rosette is needed heading into winter.

“About 50 lb N/ac total soil test plus applied fertilizer N is needed for establishment to improve winter survival; however, excessive nitrogen can make plants ill prepared (excessive leaf growth and elevated crowns) to survive cold winter temperatures.”

To balance establishment and winter survival with yield, split application of fertilizer nitrogen is needed for winter canola, he explains.

“A modest amount supports fall growth, and a second application in spring, when rosettes start to regrow, drives yield potential. For strong winter canola yields, about 150 lb/ac total spring soil test plus spring applied fertilizer nitrogen is needed for a 75–80 bushel/ac crop.”

Placement, timing & product choice

Tenuta’s research helps illustrate how timing and moisture interact.

“In six Manitoba spring canola trials from 2019 to 2021, 60 per cent of the fertilizer nitrogen was applied at seeding as urea and 40 per cent at rosette as UAN (28 0 0). When rains followed the split application, yields were comparable to applying all nitrogen at planting.

“When it stayed dry, yields were about five bushels/ac lower with the split application, highlighting the risk of leaving in season nitrogen on the surface without rain to move it into the soil.”

He also points to seed safety as a firm limit on the amount of seed placed nitrogen.

“The Prairie Agricultural Machinery Institute (PAMI) in the 1990s found maximum seed safe rates of 10–50 lb N/ac in furrow applied urea, depending on soil texture, row spacing and seedbed utilization, while Canola Council of Canada guidance for Manitoba now recommends only 0–30 lb N/ac of seed placed urea in higher pH soils because of greater risk of ammonia toxicity.

“The practical message for Ontario is to avoid or minimize seed placed nitrogen in canola and rely on banding or pre plant incorporation.”

Placement affects losses.

“The placement method of fertilizer nitrogen can reduce losses of applied nitrogen to canola,” Tenuta says.

He notes it is reasonable to expect surface applied urea or UAN in spring to lose five to 10 per cent of ammoniacal nitrogen if rains don’t wash products into the soil.

“The easiest way to prevent ammonia loss is subsurface placement banding to a depth of three inches.”

Where surface placement is unavoidable, urease inhibitors can help protect against ammonia loss, he says.

Earlier work by Tenuta’s colleagues also shows that drainage and timing interact.

“Banded urea in low spots in commercial fields was about 20 per cent less efficient when applied early in the fall compared to spring banded urea, while on higher, better drained positions, late fall banded urea performed similarly to spring banded urea.

“For Ontario fields with poor drainage or depressions prone to saturation, avoiding early fall nitrogen on those areas can help reduce losses.”

Product choice can further bridge the gap between application and crop uptake.

“Enhanced efficiency fertilizer (EEF) nitrogen products, such as nitrogen stabilizers with urease or nitrification inhibitors or polymer coated urea, can reduce losses when soils are wet and warm or when fertilizer must be applied before the crop can use it.”

Tenuta cautions, however, that growers should not expect consistent yield increases from EEF products; in his Manitoba work, they rarely produced a yield benefit in spring canola when applied at planting or in season.

“Their value is mainly in managing risk rather than boosting yield.”

Planning ahead

For Tenuta, the principle is to match nitrogen supply to crop potential while managing risk of loss.

“With good soil moisture and strong agronomy, the potential for excellent canola yields is there, particularly in winter canola.

“Growers should ensure nitrogen rates are sufficient to support that potential, while using soil testing, careful timing, appropriate placement and, where needed, EEF products to improve efficiency.”

For winter canola in Ontario, attention should focus on timely spring nitrogen applications that support rapid crop recovery after winter, he says.

“Ultimately, successful nitrogen management comes down to ensuring that nitrogen is available when the crop needs it most, particularly from rosette to flowering when yield potential is set.” BF