How and When to Apply Nitrogen to Corn

As with most tasks on the farm, timing is everything. But in addressing a nitrogen deficiency in corn, when is only half the equation — the other major consideration is how and which nitrogen fertilizers and stabilizers you use.

You need to know how timing and the method of nitrogen application can help you successfully address nitrogen deficiency in your field. We’ve created a game plan to show you how.

How to apply nitrogen to corn

You should select the best nitrogen fertilizers and stabilizers for your corn based on key factors like the time of year, your tillage methods, soil conditions, crop rotation schedule, climate, application preferences and available resources.

Nitrogen fertilizers for corn

The most common ways to apply nitrogen fertilizers are to:

Inject gas — anhydrous ammonia (NH3): Anhydrous ammonia is injected directly into the soil. It is often selected by growers as a nitrogen solution because it contains a high percentage of nitrogen (82%)¹, delivering a large amount in a single application. It is less prone to volatilization (a form of N loss) than urea and has a relatively low cost per unit compared to other nitrogen fertilizers.

Incorporate a solid — urea: Urea is a dry nitrogen fertilizer that is spread across the soil surface or incorporated into the soil. Urea is commonly used because it has relatively high nitrogen content (about 46%)², can be easily stored and transported without risk of spills or leakage, and can be either broadcast on the soil or incorporated into the soil.

Spray a liquid — urea-ammonium nitrate (UAN): UAN mixtures are liquid nitrogen fertilizers (28-32% N)³ that combine urea and ammonium nitrate dissolved in water. UAN must be placed directly into the root zone, either by being injected between corn rows or dribbled on the soil surface. This balanced combination is beneficial as it provides an immediate nutrient boost with a quick release of nitrogen, ensures a steady supply of nitrogen over time, and can be applied via either foliar sprays or irrigation systems, allowing for a more precise and uniform application.

Nitrogen stabilizers for corn

Nitrogen stabilizers are additives that can be used with nitrogen fertilizers to improve nitrogen management, increasing the efficiency of nitrogen use while reducing nitrogen losses. The most commonly used stabilizers are:

• Nitrification inhibitors, which can be mixed with nitrogen fertilizers to slow the conversion of ammonium to nitrate and reduce the risk of nitrogen leaching or denitrification.
• Urease inhibitors, which can be applied to urea-based fertilizers to slow down the change of urea to ammonia and help improve the availability of nitrogen for corn plants.
• Slow-release coated fertilizers, which are designed to release nitrogen gradually over an extended period. While technically not a stabilizer, they help provide a more consistent supply of nitrogen to corn plants and reduce the risk of nitrogen loss.

When to fertilize corn with nitrogen

The timing of nitrogen application plays a significant role in corn health and production throughout the growing season. Some growers decide to apply all nitrogen fertilizers pre-plant, while many have shifted to split-applying nitrogen both pre-plant and after corn has emerged to minimize the risk of nitrogen loss.

The optimal timing for nitrogen application can vary depending on local conditions, climate, rainfall, soil temperature and soil types.

Fall nitrogen application

The goal with fall nitrogen application is to apply a stable nitrogen source that will become available to the corn in spring. Nitrogen is often applied after soil temperatures have cooled below 50 F after harvest. The best methods of nitrogen application in cool conditions include surface application, banding or injection. Surface application can be done with broadcast spreaders, while banding or injection methods help concentrate the nitrogen in the root zone.

Many growers choose to apply nitrogen in the fall for the potential cost savings, and because equipment is more accessible and soil conditions are more conducive during this time of year.

Spring nitrogen application

If a soil analysis shows that your average nitrogen level is too low to adequately support planting, spring application may be necessary. Nitrogen levels may be lower than expected in the spring due to these factors:

1. Leaching: Heavy rainfall early in the year leaches nitrate-N downward in the soil below the root zone.
2. Volatilization: Enzymes in soil and plant residue can convert urea to free ammonia gas, which disperses without entering the soil.
3. Denitrification: Bacteria in soil that thrive in water-saturated environments convert nitrate-N into gaseous forms, preventing it from reaching roots.

Spring application can take place prior to planting or after seeds are in the ground. If weather conditions delay application, make planting your first priority to maximize yield.

Sidedress after corn emergence

Sixty-five percent of nitrogen is taken up from V8 to tasseling, when most corn varieties grow from knee-high to about neck-high in approximately two weeks. Nitrogen applications at this time are critical if corn appears to be experiencing a nitrogen deficiency.

These applications generally take place when corn reaches V4 to V6 and up to silking using one of the following methods:

• Option 1: Inject nitrogen between every row or every other row with cultivation equipment. Injection offers an advantage if rainfall is not sufficient to move surface nitrogen into the soil.
• Option 2: Surface dribble UAN between corn rows or between alternating rows.
• Option 3: Broadcast dry granular urea, UAN solutions, granular ammonium nitrate or ammonium sulfate.
• Option 4: Practice fertigation through pivots.

Note that corn fertilized through sidedress runs the risk of foliar damage or leaf burn.

Experts are available to help you make the most informed decisions all year long. Reach out to your local agronomist or regional BASF representative to help answer any remaining questions you might have related to your nitrogen application.

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Endnotes

1. “Video: Which Nitrogen Source is Right for You?” Minnesota Crop News, 1 Jan. 2024, blog-crop-news.extension.umn.edu/2020/05/video-which-nitrogen-source-is-right.html. Accessed 25 Oct. 2024.
2. “The Three Biggies: Urea, Anhydrous Ammonia, and UAN.” Minnesota Crop News, 1 Jan. 2024, blog-crop-news.extension.umn.edu/2016/05/the-three-biggies-urea-anhydrous.html. Accessed 25 Oct. 2024.
3. “The Three Biggies: Urea, Anhydrous Ammonia, and UAN.”