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New ideas block N loss

Agriculture.com Staff 03/12/2008 @ 1:29pm

It's a sobering fact that one half or more of the high-priced nitrogen that farmers will apply prior to growing this year's corn crop will be wasted. In the U.S. alone, this loss will amount to more than $1 billion. The nitrogen-use efficiency of wheat is even lower; it averages around 35% worldwide.

The major causes of nitrogen loss are leaching, denitrification, and volatilization. There are ways to manage these culprits through application methods and timing, but these often don't fit the logistics of many farming operations. However, technology is continuing to develop new products aimed at improving the economic and environmental impact of nitrogen.

Agrium's ESN (Environmentally Smart Nitrogen) is a controlled-release product that utilizes a polymer membrane that coats high-quality urea fertilizer. The membrane allows water to enter to dissolve the urea, but nitrogen must then diffuse through the membrane and into the soil. This diffusion is controlled by soil temperature and moisture, so it can be matched to the rate of crop growth.

"At soil temperatures around 65 degrees Fahrenheit, the nitrogen releases over a 60- to 80-day period," explains Agrium agronomist Alan Blaylock.

"With corn, this means you can apply it just ahead of planting, and the bulk of the nitrogen will be available 40 to 50 days later, when the crop enters its rapid-growth stage. As a result of that delay, most of the nitrogen is not available in the early spring when heavy rains often cause leaching and denitrification. You get the efficiency of sidedressing without the time and trouble of making that extra application," Blaylock says.

Winter wheat growers can apply ESN when soil is frozen, eliminating the need for split springtime applications to maximize efficiency. "Put it on in early February, and the nitrogen will become available in the spring when it is often too wet to be on the field making split applications," says Kelly Nelson, agronomist at the University of Missouri Greenley Research Center.

Compared to urea, ESN typically costs about 10¢ more per pound of nitrogen. "Our data shows the average advantage from ESN use on corn is 8 to 10 bushels per acre," says Blaylock. "In specific situations where the probability of nitrogen loss is high (such as wet, poorly drained soils), the benefit is twice that much. However, in dry conditions there is no benefit to ESN."

At the University of Illinois' Dixon Springs Research Center, agronomist Steve Ebelhar evaluated nitrogen products, separating findings for wet locations (more than 12 inches of rain within 15 weeks) and dry locations that got less. He found no difference in dry areas. But at wet locations, sidedressed UAN produced the highest average yield of 143 bushels per acre. ESN was next at a 138-bushel average, followed by urea with Agrotain (130 bushels) and UAN with AgrotainPlus (127 bushels per acre).

"In contrast, the average yield from traditional broadcast urea was 123 bushels per acre, and dribble-applied UAN was 125 bushels. It appears significant improvement in nitrogen-use efficiency can be made with these products, especially in wet years," says Ebelhar.

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