The regional Corn Nitrogen Rate Calculator (CNRC) website was recently updated with a revised Iowa N response trial database that includes data through the 2016 crop year. Last year the CNRC website was revised and the url changed to (http://cnrc.agron.iastate.edu/). The ISU Extension and Outreach publication CROP 3073 (Nitrogen Use in Iowa Corn Production) will be updated in the near future to reflect the change in N rate guidelines for Iowa. Other states are also updating databases, and those changes have been made for some states or will occur in the future for others.
With the new Iowa database, Iowa N rate guidelines have changed slightly. In addition, last year in Iowa the state was divided into two regions: the major region/area of Iowa (Main) and a Southeast (SEIA) region. Details about the two Iowa regions can be found in CROP 3073 and in the Map help area of the CNRC website.
As before, the MRTN and most profitable N rates determined from the CNRC are directly the total N fertilization amounts for each rotation, with no need to further adjust rate for the previous corn or soybean crop.