Dynamic database provides farmers with nitrogen information

By Janet Kubat Willette

Farmers who want to check their nitrogen application rates against university data have a dynamic database of online information to turn to.

The N-rate calculator, located on the Web at, calculates directly from the database every time a producer enters nitrogen cost and corn price.

With a nitrogen price of 30 cents a pound and $3 per bushel corn on corn following soybeans, the Maximum Return to Nitrogen and most profitable nitrogen rate is 124 pounds of nitrogen per acre in Iowa, according to the calculator. The profitable nitrogen rate range is from 110 pounds per acre to 141 pounds per acre.


With the same scenario in Minnesota, the Maximum Return to Nitrogen rate is 101, with the profitable nitrogen rate ranging from 88 to 116 pounds per acre.

The Minnesota data is from 50 sites. The Iowa data is from 147 sites.

The calculator went online in 2005, said John Sawyer, an Iowa State University Extension soil fertility specialist. There are more than 800 nitrogen response trails in the database from Iowa, Minnesota, Wisconsin and Illinois.

The data is updated each year, Sawyer said, so producers can feel confident that the data reflects current genetics, climate and production practices. Illinois and Iowa have data through 2006 in the calculator’s database.

The N-rate calculator gives producers guidance and is a quick tool, Sawyer said. It can be rerun when circumstances change.

The calculator is the result of a new regional approach to nitrogen recommendations, said Gyles Randall, soils scientist at Southern Research and Outreach Center in Waseca.

Prior to the new recommendations, every state had different philosophies in making nitrogen rate application recommendations. In Illinois, for example, a yield factor of 1.2 pounds of nitrogen per bushel of corn was used, Randall said. Minnesota researchers knew that factor could be 0.8.

The regional approach is based on economic returns to nitrogen. The numbers still vary across states, but it does establish a common approach to making nitrogen rate recommendations, Randall said.


It’s mind-blowing that yield goals aren’t related to the optimum nitrogen rate, said John Lamb, a University of Minnesota Extension soil scientist. Rather, the maximum nitrogen rate changes with the price of corn and the price of nitrogen. The range gives growers flexibility. Those more concerned about environmental risk may want to cut back and those worried about paying the banker may want to go toward the higher end.

Corn plants have become more efficient over time. There is also generally less weed pressure and less insect stress, Lamb said.

Some growers have been reluctant to fall in line with the economic based approach, Randall said, but the data is pretty compelling. They prefer to stick with tradition.

In Iowa, the data has been pretty well accepted, Sawyer said.

Putting data into the database also revealed geographic holes in the data, Lamb said. Minnesota was lacking data from the northwest area, the western border counties and Fillmore, Chippewa and Renville counties.

The calculator provides recommendations for corn-on-corn and corn following soybeans. There isn’t enough data to make recommendations for corn following alfalfa, Sawyer said.

Producers who apply nitrogen in the fall should hold off until the soil temperature reaches 50 degrees and stands a good chance of staying there — generally not before Oct. 25 in Minnesota. Since soils profiles are full of moisture there may be greater potential for nitrogen loss in the spring, Randall said. If a grower applies nitrogen in the fall, a nitrogen inhibitor should be used.

No nitrogen should be applied in the fall on loss soils, generally from Byron, Minn., and east.

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