Keeping nutrients in place: Research shows stabilizers, inhibitors have promise

Written by Jonathan Eisenthal

With the first ten days of October setting temperature records or near records, farm operators have to take special care with application of nitrogen fertilizers, according to experts. At these temperatures the ammonium nitrogen in fertilizer and manure can rapidly convert to nitrate and become susceptible to leaching from rain events in spring.

The addition of the nitrification inhibitor Instinct™ into swine manure used as crop fertilizer has shown promising results, according to soil scientist Jeff Vetsch who conducted the trial in 2011.

“The results so far are promising, but we recognize that this is one year of data,” said Vetsch. He noted that studies are underway in Iowa and Wisconsin as well. He will present the findings at the Crop Pest Management Short Course offered at the Crop Production Retailers Association, at Minneapolis Convention Center, Dec. 13-15.

The research looked at both time of manure application and rate of application of Instinct. They found that waiting a month, when soil temperatures had dropped, boosted yield with or without the inhibitor Instinct, but the inhibitor added an additional 10-12 bushels above the yields experienced from application of the manure alone. Vetsch, working with soil scientist John Lamb, conducted the research at University of Minnesota Southern Research and Outreach Center in Waseca.

The study looked at manure from swine finishing operations, which is the most widely available manure in southern Minnesota, according to Vetsch.

Research into this area of keeping nutrients in place for crops goes far beyond manure application. A range of products are in use with the variety of commercial nitrogen fertilizers–ammonia, urea and others. The University of Minnesota’s nutrient management working group are conducting research into five of the most common products, with research into others on the horizon. The chemical nitrogen inhibitors being tested include DCD, nitrapyrin and NDPT. Minnesota Corn Growers Association has provided funds for a portion of this research.

“A good understanding of the nitrogen cycle is essential to effective use of stabilizers or inhibitors,” said Carl Rosen head of the University of Minnesota Department of Soil, Water and Climate.

The two main categories of inhibitors include those that work chemically to prevent transformation of the fertilizer product into a form more likely to be lost to groundwater or the atmosphere. The other category is polymer coatings that create a physical barrier that delays the solubility of the fertilizer, which then delays  the transformation of fertilizer nitrogen into nitrates–the form both that the plants can use and that is most prone to loss.

“You need to know what part of the nitrogen cycle you are inhibiting,” said Rosen.

Urease inhibitor, for instance, is meant to be used when urea is surface applied on the soil to prevent it from becoming ammonia and disappearing into the atmosphere. If the producer incorporates the urea or UAN, the urease inhibitor will have little if any effect, Rosen said.

Initial work suggests that the polymer coated products may be most effective in sandy soils where irrigation is in use, according to Rosen.

“Whenever doing anything to a fertilizer, using either a coating or an inhibitor, you are increasing cost,” said Rosen. “You have to think of it as insurance, if you have a leaching rainfall, or conditions that promote denitrification, then there may be a response, but if you don’t have those conditions, then the inhibitors may not help that much. And of course, you’re making the decision to apply the inhibitors without knowing whether you’ll encounter those conditions in the coming year.”

And inhibitors are not the only route to nitrogen efficiency. Rosen told about comparison work he did where he found that he achieved higher corn yields with a split fertilizer application– starter and then two side-dressed nitrogen post emergence applications –without inhibitor use, compared to a single, pre-plant fertilizer application using an inhibitor. Research on application timing of fertilizers with and without inhibitors or coatings is in progress.

For more information on this and other nutrient research, go to:



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