The regional Corn Nitrogen Rate Calculator (CNRC; http://cnrc.agron.iastate.edu/) website was recently updated with a revised Iowa N response trial database. The changes to the suggested N rates in Iowa are small with this update. Some of the other participating states are also updating their database.
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 seven states across the Corn Belt: Iowa, Illinois, Indiana, Michigan, Minnesota, Ohio and Wisconsin.
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.
Resources for N Rate Decisions
The Corn Nitrogen Rate Calculator Web tool is located at http://cnrc.agron.iastate.edu/.
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 https://store.extension.iastate.edu/, 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 https://store.extension.iastate.edu/, 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 http://www.agronext.iastate.edu/soilfertility/