Corn Nitrogen Rate Calculator Update

March 27, 2009

By John Sawyer, Department of Agronomy

Nitrogen (N) Response Trials Added
The Iowa Nitrogen (N) response trial database was updated March 24, 2009. Response trials were added from 2008 research and several trials from older research were removed. There are now 176 trials for corn following soybean and 78 trials for corn following corn. Being able to easily update the database with recent data is one of the many advantages to this dynamic approach for corn N rate guidelines. Having new response trial data allows rapid updating with changing hybrid genetics, rotations and climatic conditions.

With the updated database, calculated N rates have changed only slightly from last fall. The table below gives the N rate at the maximum return to N (MRTN) and the profitable N rate range from the updated calculator for several N:corn grain price ratios. You can work with any price of N and corn you wish when running the calculator. Output information includes the N rate at the MRTN, the profitable N rate range, the net return to N application, the percent of maximum yield, and the selected N fertilizer product rate and cost.


What is the Corn Nitrogen Rate Calculator?
The Corn Nitrogen Rate Calculator Web tool is a resource that aids N rate decisions for corn production and is helpful in determining the effect of fertilizer and corn price on application rates. The method for calculating suggested N rates is based on a regional (Corn Belt) approach to N rate guidelines. Details on the approach are provided in the regional publication Concepts and Rationale for Regional Nitrogen Rate Guidelines for Corn. This approach and the Corn Nitrogen Rate Calculator are now being used by seven Corn Belt states: Iowa, Illinois, Indiana, Michigan, Minnesota, Ohio, and Wisconsin; with Michigan and Ohio being added this year.


Resources for N Rate Decisions
The Corn Nitrogen Rate Calculator Web tool is located at

The regional publication Regional Nitrogen Rate Guidelines for Corn, PM 2015, can be ordered through any ISU Extension county office, on the Web through the extension online store , or by calling 515-294-5247. An electronic copy of the publication is available at

The ISU Agronomy Extension Soil Fertility Web site is located at

John Sawyer is professor with research and extension responsibilities in soil fertility and nutrient management

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