Iowa State University Extension has several resources to help farmers make corn nitrogen rate application decisions, including a corn N rate calculator. ISU soil fertility specialist John Sawyer has updated that management tool for 2009.

The Iowa nitrogen response trial database for the calculator was updated in late March. Yield response trials were added from 2008 research and several trials from older research were removed. There are now 176 trials for corn following soybeans and 78 trials for corn following corn.

"Being able to easily update the database with recent data is one of the many advantages of using this approach for corn N rate guidelines," says Sawyer. "Having new response trial data allows rapid updating of the calculator with changing hybrid genetics, crop rotations and climatic conditions."

New nitrogen response trials added

With the updated database, calculated N rates have changed only slightly from last fall, he says. 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," notes Sawyer. "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 tool that helps you make 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." Sawyer says 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.

Helpful resources for N rate decisions

The Corn Nitrogen Rate Calculator Web tool is located at extension.agron.iastate.edu/soilfertility/nrate.aspx.  

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 www.extension.iastate.edu/Publications/2015.pdf.  

The ISU Agronomy Extension Soil Fertility Web site is located at extension.agron.iastate.edu/soilfertility.