Tools to protect costly nitrogen investment

DEKALB, Ill. — With the harvest near the finish line, corn growers turn toward their nitrogen plans for the 2026 growing season that may include a fall application.

Nitrogen is critical for corn growth, but its volatility often leaves farmers searching for the best source, rate and timing of the vital input.

Fall applications are convenient, but can be risky due to potential losses from leaching, denitrification and volatilization.

Pre-plant nitrogen has a lower risk of loss than fall-applied nitrogen, but can be delayed by weather, potentially delaying planting beyond the optimum window.

Having a nitrogen strategy, spreading nitrogen applications throughout the season and using stabilizers can help protect nitrogen investments and improve efficiency.

“I can’t put a number on it, but I do have a fair amount of people who do run fall anhydrous applications,” said Crystal Williams, Pioneer agronomist in DeKalb, Lee, Ogle and Whiteside counties in northern Illinois.

Recommendations

A starting point for a fall nitrogen applications is soil temperature.

“Make sure that soil temperatures are 50 degrees and below, as well as trending downward. We definitely had some fields applied last year and a couple days later it was 80 degrees outside. That’s never a good day,” Williams said.

Cooler soils slow the activity of bacteria that convert ammonium to nitrate, which is the form most vulnerable to leaching and denitrification.

It is also important to stick with ammonium sources, such as anhydrous ammonia, and avoid nitrate-based fertilizers when applying in the fall.

A key challenge in nitrogen management is that once nitrogen converts to nitrate in the soil, a process called nitrification, it becomes highly mobile and susceptible to leaching or denitrification, a microbial process that occurs in water-saturated soils.

Denitrification not only reduces nitrogen available to crops, but also releases nitrous oxide, a potent greenhouse gas. These losses are especially problematic in the fall and spring, when soil is cool and wet and plant uptake is low.

Stabilizers

Nitrogen stabilizers help mitigate those risks by slowing down the chemical process that lead to nitrogen loss.

“Utilizing a nitrogen stabilizer has been a really key one and not all of them are created equally. Our N-Serve and Instinct NXTGEN nitrogen stabilizers stand out to me. N-Serve and Instinct and those nitrapyrins nitrogen stabilizers are not water-based, and keeping that nitrogen in the root zone where it’s needed is extremely important,” Williams said.

Nitrification inhibitors, such as nitrapyrins, delay the conversion of ammonium to nitrate, keeping nitrogen in a more stable form that’s less likely to leach or be lost to denitrification. These products are especially effective in fall applications, as they remain active longer in cool soil conditions.

“I found that based on the total amount of nitrapyrin sold in the industry last year that resulted in 21 million pounds of nitrogen that did not end up in rivers because of utilizing that. That’s pretty significant,” Williams said.

“We even decrease greenhouse gases by 51% when we utilize a nitrapyrin and decrease leaching by 16%. So, it’s definitely a tool.

“Some people go the approach of just add extra nitrogen and that’s not really the most effective use. It’s going to disappear anyway even more back into our waterways.”

Urease inhibitors, such as NBPT, are used with surface-applied urea or UAN to slow the conversion of urea into ammonia gas, which can be lost to the atmosphere. This is particularly useful in no-till or reduced-tillage systems where urea is not incorporated into the soil.

NBPT works by blocking the urease enzyme that drives this conversion, buying time until rainfall or irrigation can move the nitrogen into the soil.

While yield responses to nitrogen stabilizers can vary depending on conditions, they provide an important form of insurance against unpredictable weather and nitrogen loss.

The greatest value of nitrogen stabilizers can be seen when nitrogen is applied well before the crop needs it, such as in fall or early spring, or in fields prone to nitrogen loss due to poor drainage, sandy soils or tile drainage systems.

By using the right stabilizer with the appropriate nitrogen source and application timing, farmers can significantly improve nitrogen use efficiency, protect their investment and reduce environmental impact.

“I do have a fair amount of people turning towards split applications,” Williams said. “They apply some nitrogen in the fall and then later as a post-pass or sidedressing in-season is a really great way because that corn crop uses 80% of those nitrogen needs after V6.

“We need to make sure that we still have that nitrogen available later in the season. When the heat and the moisture both are taking away from our nitrogen supply, that’s where we want to make sure we had it when we need it.”