Time-release nitrogen: Will it work with northern spring wheat?

CROOKSTON, Minn. -- Research being conducted at the University of Minnesota's Northwest Research and Outreach Center in Crookston may lead to use of time-release nitrogen fertilizer products for spring wheat producers in the Northern Plains.

CROOKSTON, Minn. -- Research being conducted at the University of Minnesota's Northwest Research and Outreach Center in Crookston may lead to use of time-release nitrogen fertilizer products for spring wheat producers in the Northern Plains.

"I'm excited by this potential because nitrogen is the most limiting nutrient we have in production," says Albert Sims, soil scientist with the

research center in Crookston. "It is the highest-cost input as far as fertilizers are concerned, and it is also one of the critical nutrients, in terms of environmental issues."

Nitrogen loss

Producers apply very precise amounts of nitrogen each year before spring wheat planting. Once the nitrogen is applied, it has a limited time in the soil before it begins to lose it ability to provide nourishment to growing plants. A certain amount of it eventually ends up in the crop, and some will remain in the residue, but it is not unusual for there to be a 20 percent to 30 percent loss of the original nitrogen applied, Sims says.


"We can't account for it," he says, adding that there are several different mechanisms that could be affecting the loss.

Nitrogen can be lost through ammonia gasification, or evaporating into the air. It can be lost through denitrification, a process by which microorganisms steal the oxygen from the nitrogen, leaving it to, again, gasify and evaporate into the air. Nitrates also are very water-soluble and may leech down below the root zone.

The theory behind what are termed "enhanced efficiency products" is in protecting that nitrogen as long as possible so that it's released as close as possible to the time that the plant needs it. After that, the plant will do the rest.

"The plant can outcompete the other mechanisms," Sims says. "In the case of wheat, for the most part, the best management in our spring wheat is pre-plant applications of nitrogen. We've tried split applications, we've tried all kinds of things, and we just can't beat making sure we have sufficient nitrogen pre-plant for spring wheat."

Enhanced efficiency products

Sims' studies, centered on these enhanced fertilizers, are going into their fifth year in fields around northwestern Minnesota. The technology is not new. Enhanced fertilizers have been in use elsewhere for years.

"They used to be known as slow-release," he says. "They are probably more common in very high-value cash crops like vegetables, ornamentals and turf grass."

Enhanced fertilizers use physical or chemical processes to reduce nitrogen loss by delaying release of the nitrogen molecules.


Agrium's Environmentally Safe Nitrogen product, or ESN, utilizes a poly-coating to temporarily protect the nitrogen molecule. Water passes through this physical barrier and diffuses the nitrogen molecule inside. The liquefied nitrogen then seeps back out into the soil.

A different enhanced efficiency technology also coats the nitrogen molecule but incorporates a catalyst that triggers the conversion of urea to ammonia and then to nitrate.

A third technology embeds Agritain into the nitrogen molecule. Agritain inhibits both conversion of urea into ammonia and the conversion of ammonia into nitrate.

"So it's got a double-whammy," Sims says.

However, these products cost 8 cents to 12 cents more per pound than regular nitrogen, so gaining enough benefit from these technologies to make economic sense is necessary.

Site testing

Sims has concluded four years of field testing on one of the enhanced efficiency products, Agrium's ESN, with mixed results. ESN's use of diffusion, a physical process, is dependant on both temperature and moisture.

"The warmer it is, the faster that diffusion process occurs," he says. "That same warmth also triggers the tillering in the plant."


The theory is that when the two mechanisms are triggered together, the plant gets fed when it is most hungry for nitrogen. But weather doesn't always cooperate.

"I have one site year where there was no difference between ESN and urea. I have one site year where I increased wheat yield by about seven bushels per acre," he says. "But this last year didn't turn out that way, and, in fact, the urea was more effective than the ESN."

The poorer results may be because of moisture issues, Sims says.

"I think the reason had nothing to do with the quality of the product, but that we had a very dry spring. That goes to the science of how these enhanced fertilizer sources work," he says.

Since moisture is key to the release mechanism in ESN, Sims thinks dry weather may have interrupted that process.

Three inches of rain fell early on the site that produced matched performance between regular nitrogen and ESN. After that, it was "bone dry" for the rest of the year.

In this case, Sims theorizes that the problem was the lack of moisture during tillering. Plants are going into rapid growth during tillering and therefore trying to take up as much nitrogen as possible.

"I think nitrogen got released, but it was just so dry the wheat couldn't take advantage of it," Sims says. "That same year, we had a trial . . . and there we got very timely rains, all year long, and we got that seven-bushel enhancement from ESN."


In 2008, Sims planted two sites when the weather still was cold and dry. In both cases, the regular nitrogen performance bettered that of the ESN.

"So while the diffusion process is temperature-dependant, it still has to have water," he says.

Early conclusion

Next year will be last for Sims' field trails and, depending on his results, he then may move into greenhouse trials. Right now, the jury still is out on it, Sims says.

"I've seen data from other places," he says. "There is a potential for real good benefit from products like ESN. But because we're dry-land agriculture and we can't control moisture, that may be the risk factor that we can't calculate into the equation."

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