A warmer than normal winter coupled with dry weather through February has led to surprisingly good field conditions in much of southern Ontario. While it looks like it could be an early spring, we know that the weather can change rapidly this time of year.

Some are questioning whether it makes sense to take advantage of the warm weather, and make their early nitrogen applications, or if it is best to hold off those applications to a more normal timeframe, knowing that the weather could change. Let’s look at a few scenarios below.

Is it too early to apply nitrogen to winter wheat?

At this point in early March, much of the winter wheat crop has just started to green up  and is not yet growing rapidly enough to take up much more nitrogen (N) than what the soil is able to provide. Rapid uptake of N does not occur until stem elongation (growth stage 30). Applying N too early can increase the risk of N losses through leaching and denitrification. With potential for more winter weather ahead of us, there is a likelihood that a good portion of the N applied will be lost and unable to be utilized by the wheat plant.

If your early planted wheat has many tillers and is thick, there is no need to rush early N applications. On early planted wheat, a big supply of early nitrogen can also lead to increased lodging risk.

For late planted winter wheat fields, an early N application can help promote spring tillering, but it is important to wait until the plant has broken dormancy and is able to access and utilize N. If applied too early, there is too much potential for losses to the environment and your wallet.

If you have late planted wheat with little or no tillers, you may want to consider an early N application; however, it is critical to ensure the wheat has broken dormancy and is actively growing. Winter wheat will have broken dormancy once there has been seven consecutive days of average daily temperatures above 0˚C. You can also confirm your wheat has broken dormancy by digging up plants and identifying new white root growth.

Is it too early to apply nitrogen to winter canola?

The winter canola crop has started to green up and will continue to grow and take up nitrogen whenever temperatures are above zero. However, early season application of nitrogen and sulfur is not without its risks. Like winter wheat, high concentrations of N in the soil during a period without rapid growth leads to greater potential N losses through denitrification or leaching.

Crop development is primarily driven by temperature. Applying nitrogen will not increase the rate of development and cause early flower bud production or bolting. If canola is growing significantly at this time, depending on location and the forecast there may be value in applying some N now to feed the growing crop. Once the extended forecast looks more favourable, the balance of N can be applied. It is important to assess plant health before applying nitrogen and sulfur. Confirm that the growing point is green and new leaf tissue is developing, that plant crowns are not hollow or rotten inside, and that roots are not mushy and rotten.

A cold snap in late April or May is not uncommon, and canola will likely be bolted by that time and at risk of injury. However, the variety Mercedes has been shown to tolerate short periods at temperatures as low as -4°C after bolting has started.

Figure 1. For crops like winter canola (pictured), winter wheat, and grass hay, early N applications can be beneficial, but growers should be aware of the risks of early application, especially the potential for N losses.

Is it too early to apply nitrogen to forages?

At this point in early March, perennial forages have not yet started to green up. The potential for N loss is high, since the crop is not growing and there is still a good chance of winter weather in the next month or so.

Legumes do not start fixing N until soil temperatures are warmer than 10˚C. Grasses will break dormancy and start growing at cooler temperatures, so there is an opportunity to increase first cut yield in mixed or grass stands with an early N application while soils are still cool. Make sure grasses have greened up and are growing before applying N. If the stand is 33% to 50% legumes, apply 60 kg N/ha (55 lb/acre). If the stand contains less than 33% legumes, apply 23 kg/tonne (45 lb/ton) of expected dry matter yield.

Many pasture managers struggle to maintain forage quality in the late spring and early summer, because spring grass growth rates far exceed animal demands. An early spring nitrogen application should be avoided if surplus forage in these paddocks cannot be harvested as stored forage.

Is it too early to apply nitrogen to corn?

At this point in the season, it is far too early to apply nitrogen to fields intended for corn. With nice conditions in the field, there has been talk of applying nitrogen ultra-early to get ahead of the spring workload and give time for incorporation well before planting. Nitrogen application at this point is a recipe for huge loss potential. Rapid uptake of N in corn does not occur until the V6 stage (roughly knee high, or mid to later June for many parts of Ontario), which is a very lengthy time to leave loitering nitrogen in the soil and to potentially be lost to leaching or denitrification.

Applying N that will not be incorporated immediately can also be risky. Extremely dry conditions after planting in 2023 led to some relatively high volatilization losses due to the lack of significant rainfall to incorporate N fertilizers applied in early May. This has led to some rethinking their nitrogen program to avoid these losses.

There are ways to reduce the impact of early season N loss, but applying months before the crop will need it is not a profitable venture.

If I use nitrogen inhibitors, is it still too early?

Nitrogen inhibitors can be used to slow down the natural conversion of N fertilizers to losable forms in the soil. Urease inhibitors help prevent volatilization losses of ammonia by slowing the breakdown of urea, while nitrification inhibitors help prevent denitrification or leaching losses by slowing the conversion of ammonium fertilizers to nitrate. The ideal scenario is one where an inhibitor can slow N conversion just until the crop can utilize the N in a plant-available form.

When using N inhibitors, it is important to realize that these products work through depressing the activity of enzymes or bacteria, and over time, they lose their efficacy. Urease inhibitors can reduce ammonia losses for approximately 7 to 14 days, while nitrification inhibitors may reduce nitrate losses for 25 to 70 days. Effectiveness of N protection is determined by the product used, as well as soil moisture and temperature.

In winter wheat and winter canola, early N applications followed by cool, wet conditions are generally most at risk for losses through denitrification or leaching. A nitrification inhibitor may have a fit in these scenarios, especially if heavy rains and cool conditions are forecasted after application. However, use of an N inhibitor will not prevent all losses, and full rate application using N inhibitors is still not recommended.

On grass hay, a very early application of N may benefit from the addition of nitrification inhibitors as well if the forecast looks cool and wet after application. Timing is important though, and later applications may not see this same benefit as loss potential decreases in an established crop.

In corn, N application this early, even with use of urease or nitrification inhibitors, is still too risky to recommend. It is much better to apply closer to planting or in-season to prevent N loss and improve profitability.


Brown, C., editor. (2017). Agronomy Guide for Field Crops, Publication 811. Ontario Ministry of Agriculture, Food, and Rural Affairs.
International Plant Nutrition Institute. Nutrient Source Specifics No. 25. Urease Inhibitors.
International Plant Nutrition Institute. Nutrient Source Specifics No. 26. Nitrification Inhibitors.