Iowa nitrogen (N) response trial data for the 2016 crop year was recently added to the Corn Nitrogen Rate Calculator (CNRC). The regional web site provides a process to calculate economic return to N application (the Maximum Return to Nitrogen, or MRTN) with different nitrogen and corn prices and to find profitable N rates directly from recent N rate research data. The method uses a regional approach used by several Corn Belt states in determining recommended corn N rates.
With the new Iowa database, Iowa N rate guidelines have changed slightly (that is, comparing the previous MRTN and ranges with the newly revised MRTN and its ranges). In addition, last year Iowa 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 Iowa State University Extension publication, Nitrogen Use in Iowa Corn Production (CROP 3073), and also in the Map help area of the CNRC website. As before, the MRTN and the most profitable projected 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.
Also, CROP 3073 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.
In addition, the MRTN concept is fully explained in the ISU publication, Concepts and Rationale for Regional Nitrogen Rate Guidelines for Corn (PM 2015).
For more information, contact Dr. John Sawyer, ISU professor of agronomy and an extension soil fertility and nutrient management specialist, (515) 294-1923, firstname.lastname@example.org.
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