You should visit the newly formatted and revised Corn Nitrogen Rate Calculator (CNRC) website. The site has a new url ( http://cnrc.agron.iastate.edu/ ). For Iowa, there are now two regions, the Main Iowa area and a Southeast Iowa area (SEIA) – see the descriptions below. The Iowa corn following corn and corn following soybean N rate response trial databases have also been updated, so suggested N rates have changed somewhat. Check out the site and try different N and corn prices and see how they affect suggested N rates. The site is also more user friendly on smartphones.
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. Rates from the CNRC will now match those in Iowa State University Extension and Outreach Publication CROP 3073, Nitrogen Use in Iowa Corn Production.
Iowa Geographic and Soil Regions – N 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.
Map of Iowa soil regions from USDA-NRCS.
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- Retired Nitrogen Soil Fertility Specialist and Professor