LINCOLN, Neb. -- As corn prices rise and nitrogen fertilizer prices are lower in some cases than in recent years, corn growers may want to increase the amount of nitrogen they apply to their corn fields. However, University of Nebraska-Lincoln soil specialists caution against excessive nitrogen application.

"With corn prices currently in the $3.60 to $3.80 per bushel range and nitrogen in the 25 cent to 45 cent per pound range, the corn-to-nitrogen price ratio can range as high as 13-to-1 to 15-to-1," said Richard Ferguson, UNL soils specialist. "However, the incremental yield increase with more fertilizer is relatively small and the risk of leaving substantial residual nitrate-nitrogen in the soil becomes much higher."

To discourage over-application of fertilizer, UNL soil scientists are recommending a maximum 10-to-1 corn-to-nitrogen ratio and a minimum 5-to-1 corn-to-nitrogen ratio when calculating economic nitrogen rates for corn.

"We believe these limits will not significantly impact profit potential for Nebraska's corn growers and will allow for good stewardship and minimize excessive nitrogen applications from seeping into and contaminating groundwater," said Achim Dobermann, soil fertility/nutrient management specialist.

The demand for corn is being driven mostly by ethanol production and Nebraska corn growers anticipate a much more positive economic outlook for 2007 than in recent years.
From 2005-2006, producers were facing expensive nitrogen fertilizer prices and low corn prices. This, combined with recent UNL research evaluating optimal fertilization rates for irrigated corn, led UNL researchers to set nitrogen recommendations at a base price ratio of 8-to-1, where the value of corn is eight times the value of a pound of nitrogen fertilizer, Doberman said. With lower price ratios of 5-to-1 or 6-to-1 in 2006, the economic adjustment to nitrogen fertilizer recommendations reduced rates from this base by 20 to 40 pounds per acre.

"These lower rates slightly reduced yield potential, but more importantly maximized profit," Doberman said.

When applying nitrogen this spring, corn growers also must take into account all nitrogen sources, Ferguson said.

"In Nebraska, the UNL recommendation procedure for corn is based on accurate soil sampling every three to five years for organic matter, annually for residual nitrate-nitrogen and accurate yield goal estimation using at least five years of yield history," Ferguson said.

It also is important to account for other nitrogen credits which may be available, such as legumes as a preceding crop, nitrate in irrigation water and nitrogen derived from manure.

For more information about nitrogen rates, the most current nitrogen rate calculator for corn is available as a downloadable Excel spreadsheet from UNL's soil fertility Web site at The most recent version is called UNL N calculator 2007.xls.

Other UNL soil fertility faculty involved with this research and in making these recommendations include: Ken Cassman, Gary Hergert, Charles Shapiro, Dan Walters and Charles Wortmann.

SOURCE: University of Nebraska news release.