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Nailing down nitrogen

Agriculture.com Staff 10/07/2008 @ 1:44pm

Nitrogen management has long been one of the biggest challenges most corn growers face each year. The run-up in nitrogen prices over the past two years has greatly exascerbated the situation.

"The bottom line on nitrogen use in corn is that we're dealing with a biological system that interacts with everything else under the sun, including the sun," says Purdue agronomist Bob Nielsen.

When nitrogen prices were somewhat stable and relatively cheap compared to corn, optimum nitrogen rates didn't vary much. The common approach was to apply enough nitrogen to ensure that corn was never deficient in that nutrient.

The nitrogen rate was often based on yield goals. But evidence continues to mount that there isn't much correlation between yield levels and nitrogen rates. And several land-grant universities have moved away from using yield goals as a basis for nitrogen decisions.

"Throughout the Midwest, there is a growing movement away from yield-based N-rate recommendations toward data-driven recommendations that are sensitive to N and grain prices," says Purdue agronomist Jim Camberato. "This so-called new approach to N rates is not necessarily new, but it simply links documented yield responses to N with the relative economics of grain price and N cost. In other words, maximum dollar return to nitrogen."

There is a regional publication about the new approach, which is referred to as maximum return to N or MRTN, available online at www.agronext.iastate.edu/. Scroll down to Soil Fertility. Under Current Topics, click on Concepts and Rationale for Regional N Rate Guidelines for Corn.

The MRTN approach is being used in Illinois, Indiana, Iowa, Michigan, Minnesota, Ohio, and Wisconsin.

Higher nitrogen prices are also increasing the interest is split applications of nitrogen.

"The main reason that sidedress N applications will be more efficient in the long haul is that there is a shorter calendar window between application and plant uptake for sidedress than for preplant applications," says Nielsen.

"The shorter time period means there are fewer opportunities for heavy rainfall events and nitrate-N loss. Thus, nitrogen-use efficiency will be greater, on average," he says.

"Sidedress applications often do not add dollar cost to your fertilizer program. But they obviously alter the logistics of your farming operation and are more at risk from rainy weather prior to too-tall corn," he adds.

Nitrogen management has long been one of the biggest challenges most corn growers face each year. The run-up in nitrogen prices over the past two years has greatly exascerbated the situation.

In an effort to protect expensive nitrogen, some growers are taking a fresh look at nitrification inhibitors, urease inhibitors, coated urea, and other products that promise to protect nitrogen from leaching, denitrification, and volatilization.

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