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Should You Use a Nitrification Inhibitor With Fall Nitrogen?

Nitrification inhibitors can protect fall nitrogen against loss and increase the amount of nitrogen present in the ammonium form the following spring.

Soil temperatures are dropping and moving toward the 50°F. threshold for fall nitrogen (N) applications. If you’re thinking about fall applications, do you know if you should you use an inhibitor? The University of Minnesota (U of M) shared results from fall nitrification inhibitors in a Minnesota Crop News article. Here’s what they found.

“Our research shows that nitrification inhibitors can protect fall N against loss and increase the amount of N present in the ammonium form the following spring, as long as best practices are followed,” explains Jeff Vetsch, University of Minnesota soil scientist.

Nitrification Inhibitors vs. Urease Inhibitors

The two main types of inhibitors are nitrification inhibitors and urease inhibitors.

“Urease inhibitors, like NBPT, NPPT, Agrotain Ultra, Factor, and Limus, protect fertilizers from ammonia volatilization,” says Vetsch. “Generally, they are not needed with fall applications due to cool temperatures and incorporation.”

Nitrification inhibitors, which include Nitrapyrin, N-Serve, Instinct, and DCD, stop or slow the nitrification process, says Vetsch. “This keeps fertilizer N in the NH4+ form longer, which protects it from leaching and denitirification losses.”

U of M scientist found the greatest potential for a return on investment with nitrification inhibitors is with fall anhydrous ammonia on medium- and fine-texture soils in south-central, southwest, and west-central Minnesota.

Apply ammonia after soil temperature at the 6-inch depth is less than 50°F. and trending downward, says Vetsch.

For more on fall N applications, check out 4 Steps for Fall Nitrogen Applications.

“There is also potential for a return on investment with nitrification inhibitors on fall-applied liquid swine manure, especially when manure is applied in early October, when soil temperatures are above 50°F.,” he says.

Long- and Short-Term Inhibitor Research

A 15-year study at Waseca showed addition of N-Serve to fall-applied ammonia increased corn grain yields 9 bushels per acre. It also increased N use efficiency and decreased NO3 losses in tile drainage, says Vetsch.

However, in seven of the 15 years, spring-applied ammonia without N-Serve had 12 bushels per acre greater corn yields than fall-applied with N-Serve. In recent years, adding N-Serve to fall-applied anhydrous ammonia has increased yield about 50% of the time, and the average yield increase is about 8 bushels per acre.

A four-year study at Waseca found adding Instinct to liquid swine manure applied in early October increased corn yields 7 to 10 bushels per acre. Delaying manure application until early November produced equal yields, says Vetsch.

“Always remember to choose a proven nitrification inhibitor, one with years of unbiased research data,” says Vetsch. “Inject your N source and NI whenever possible to maximize effectiveness.”

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