Farmers urged to protect fall nitrogen

October 2, 2025 | Kriss Nelson

Harvest is in full force, which means some farmers will soon shift their focus to fall nitrogen applications.

Alex Schaffer, Iowa Soybean Association (ISA) research agronomy lead, encourages farmers to wait until soil conditions are optimal for nitrogen applications and consider protecting the nutrient with a stabilizer.

Without both, much of the investment is at risk for loss before corn can utilize the nutrient.

“Soil temperatures need to be 50 degrees and falling. Not 50 and holding, and not 50 and rising,” says Schaffer.

Everything that goes out in the fall, whether manure or anhydrous ammonia, in his opinion, should have a stabilizer.

“It’s hard to predict what the weather’s going to be, if it is going to freeze solid, or if it’s going to be warm and rainy,” he says. “When soils aren’t frozen, the biology will still be converting ammonium to nitrate.”

Stabilizer strategy

“When we talk about stabilizing nitrogen, what we’re really doing is keeping nitrogen in the ammonium (stable) form for as long as we can,” says Ty Stender, a nitrogen stabilizer specialist for Corteva in northern Iowa.

Corteva offers two nitrogen stabilizers: Instinct NXTGEN for manure, UAN and urea, and N-Serve for use with anhydrous ammonia. Both products use nitrapyrin as the active ingredient, but are tailored for different nitrogen sources. The difference lies in the formulation: N-Serve’s oil base makes it well-suited for use with anhydrous ammonia, while Instinct NXTGEN encapsulates the same active ingredient, ensuring it remains stable when applied with manure, UAN or urea.

“Instinct and N-Serve protect nitrogen by taking Nitrosomonas bacteria, the bacteria that convert the nitrogen from the stable form to the non-stable form, and put it in a state of stasis. We’re really not treating the nitrogen itself. We’re actually treating the acre,” says Stender.

Stender emphasizes that nitrogen stabilizers are not an excuse to apply nitrogen before the soil reaches the right temperature.

“A common misconception that we hear is that we are stabilizing our nitrogen in the fall to protect it through the winter,” says Stender. “However, if we make timely applications when soil temperatures are cool, our nitrogen stabilizer is really there to delay the nitrification process and protect the nitrogen in the spring when the soil temp warms up and we receive those large spring rains.”

When timely nitrogen applications are made late in the fall, as soil temperatures continue to drop, the nitrification process slows until it nearly halts when the soil freezes. Very little nitrogen converts over winter.

“A stabilizer provides insurance if soils briefly warm during a January thaw, but its biggest value comes in the spring,” Stender adds. “As soils warm quickly and heavy rains arrive, nitrogen is most vulnerable to leaching and denitrification as the nitrogen continues to convert to nitrate. This process is delayed by utilizing N-Serve or Instinct NXTGEN.”

Protecting your investment

Using nitrogen stabilizers ensures plants receive nitrogen when they need it, protecting your investment and helping prevent wasted inputs.

According to Stender, rapid nitrogen uptake occurs starting around the V6 growth stage, and by the VT growth stage, about 65-70% of plants' nitrogen uptake is completed, which means there’s still 30 to 35% needed after tassel.

“We’re applying nitrogen well in advance of when the plant needs it, so we’re trying to make sure we keep it in the root zone as long as possible,” says Stender. “Protecting your nitrogen investment means not running short on nitrogen later in the year, and that you won't need to add as much supplemental nitrogen because your original application is still available for the plant.”

Schaffer says that on-farm trials comparing fields with and without stabilizers have demonstrated a measurable yield increase when stabilizers are utilized.

“We have seen some big results with 18- to 25-bushel yield responses from using stabilizers,” says Schaffer. “That may not happen every year, but it was a result of the weather that year. To me, there is no reason not to use a stabilizer because you just do not know what the weather’s going to do.”

According to Stender, using Instinct NXTGEN with fall manure applications has resulted in an average increase of 10 to 12 bushels per acre compared with the same fall manure application without the stabilizer. In a three-year study by Iowa State University, the difference was more than 18 bushels.

For N-Serve applications with anhydrous, Stender reports a 7 to 10 bushels per acre increase compared with applications without the stabilizer.

An environmental impact

From an environmental and stewardship standpoint, protecting nitrogen applications is the right thing to do.

“We don’t want to over-apply nitrogen just to ensure we’ve got enough. We want to apply the right amount at the right time, and then do what we can to ensure it’s still there when we need it,” says Stender.

N-Serve reduces nitrate leaching by 16% and increases soil nitrogen retention by 28%, he says.

“That’s a big deal for water quality,” Stender notes.

Using stabilizers also reduces greenhouse gas emissions.

“Nitrogen can be lost through denitrification, which converts nitrogen to nitrous oxide gas,” says Stender. “That’s a potent greenhouse gas. We don’t see it, we don’t think about it, but N-Serve and Instinct stabilizers reduce that loss by nearly 51 percent.”

Manure protection

The importance of stabilizers in manure is often overlooked. Even though farmers often apply manure before the soil reaches optimum temperatures.

“That’s one of our biggest opportunities to be protecting nitrogen in manure applications,” Stender says. “It’s probably the most at risk of all the nitrogen we apply because it’s applied the earliest, and it’s also the most variable of our nitrogen sources.”

Stender recommends Instinct NXTGEN application rates based on soil temperature:

• 36 ounces per acre when soils are between 50 and 60 degrees and between Oct. 1 and Nov. 1

• 24 ounces per acre when soils are 50 degrees and after Nov. 1

• 48 ounces per acre when soils are above 60 degrees and before Oct. 1

Anhydrous planning

Schaffer advises farmers to use the Nitrogen Fertilizer Application Consult (N-FACT) tool when making their fall anhydrous application plans.

This decision support tool leverages data from the Iowa Nitrogen Initiative on-farm nitrogen rate trials with cropping systems modeling. Farmers can determine their optimum nitrogen rate under various scenarios by selecting factors such as location, anticipated crop year weather, residual soil nitrogen, crop rotation, planting date and fertilizer/crop pricing.

“For the 2025 crop year, most residual nitrogen is already taken up or leached out,” Schaffer says. “Using the N-FACT tool with the consideration of a low residual nitrate level helps guide the right nitrogen rates.”

Both Schaffer and Stender recommend that, in addition to using N-Serve stabilizer, farmers split-apply nitrogen in the fall and spring.
“Protecting your anhydrous application with a stabilizer is one way, and split-applying nitrogen is another,” says Stender. “The best approach is dialing in your rate and using a combination of those practices. That makes the most of the application.”

Spring trial opportunity

Stender says there are myths surrounding the use of stabilizers in the spring.

“The truth is, Iowa farmers do a good job of protecting fall nitrogen applications. However, in the spring, not much nitrogen is stabilized,” says Stender. “There are two common reasons: first, growers think they don’t need to stabilize their nitrogen because it’s applied closer to when the plant needs it. Second, there’s a myth that stabilizers tie up nitrogen so the plant can’t access it.”

To debunk these myths, ISA is partnering with Corteva to conduct on-farm research using replicated trials of spring anhydrous applications with N-Serve and without it.

Schaffer is calling on 10 farmers who use spring anhydrous and are considering whether adding a stabilizer would benefit their operation to take part in the trial.

An ISA research agronomist will take soil samples from both strips every two weeks for up to eight weeks after application to determine the conversion rate from ammonium to nitrate with and without N-Serve.

“That’s the big value in the trial,” says Schaffer. “Even if you don’t see a yield response from using the product, at least we will have some good data on how microbes are working in the soil with different treatments.”

For more information on stabilizers, contact your ISA research agronomist at agronomy@iasoybeans.com or visit Corteva’s website at https://www.corteva.us/products-and-solutions/crop-protection/Nitrogen-Stabilizers.html.

Written by Kriss Nelson.

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