Corn Nitrogen Rate Calculator Website Update

May 3, 2016
ICM News

The regional Corn Nitrogen Rate Calculator (CNRC) website was recently updated with a fresh look and a revised N response trial database. The concept and calculation process remains the same. The CNRC website url has changed to ( The site is now more user friendly on smartphones.

With the new database, state N rate guidelines may have changed (including in Iowa), as well as Iowa now having two regions: the major region/area of Iowa (Main) and a Southeast (SEIA) region. The two regions of Iowa in the CNRC will match Iowa State University publication CROP 3073. Details about the two Iowa regions can be found in CROP 3073 and in the Map help area of the CNRC. As before, the MRTN and most profitable N rates determined from the calculator are directly the total N fertilization amounts for each rotation, with no need to further adjust rate for the previous corn or soybean crop.

If you are not familiar with the Corn Nitrogen Rate Calculator

The CNRC is an online tool that allows determination of N application rates for corn production and is helpful in determining the effect of fertilizer and corn price on needed 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 was first implemented in 2005 and the CNRC is the current university N rate guideline system used in six states across the Corn Belt: Iowa, Illinois, Michigan, Minnesota, Ohio, and Wisconsin.

Iowa Geographic and Soil Regions

Nitrogen response trial sites for Iowa are now grouped by two geographic regions. The main Iowa region is the majority of the state. A second Iowa region is Southeast Iowa, which includes Soil Regions 21, 22, and approximately the south half of Soil Region 17 (generally about south of highway 92). Soils for trial sites in the Southeast region include poorly drained soils like Haig, Kalona, Macksburg, Mahaska, Nira, Otley, Richwood, Taintor, and other similar soils. If soils in the Southeast region are better drained, then use the main Iowa region.

Iowa map of soil regions from the USDA/NRCS.

Resources for N Rate Decisions

The Corn Nitrogen Rate Calculator Web tool is located at

Publication CROP 3073, Nitrogen Use in Iowa Corn Production, can be ordered through any ISU county extension and outreach office, downloaded from the ISU Extension Online Store at, or by calling (515) 294-5247.

The regional publication Regional Nitrogen Rate Guidelines for Corn (PM 2015) can be ordered through any ISU county extension and outreach office, downloaded from the ISU Extension Online Store at, downloaded from the CNRC website, downloaded from the ISU Agronomy Extension Soil Fertility website, or by calling (515) 294-5247.

The ISU Agronomy Extension Soil Fertility website is located at


Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Integrated Crop Management News, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on May 3, 2016. The information contained within may not be the most current and accurate depending on when it is accessed.