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Soil Fertility

Questions? Contact John Sawyer

Professor
Extension Soil Fertility Specialist
Phone: (515) 294-7078
Email: jsawyer@iastate.edu

Antonio Mallarino

Professor, Soil Fertility
Phone: (515) 294-6200
Fax: (515) 294-2458
Email: apmallar@iastate.edu

Soil Fertility Home Page

Welcome to the Iowa State University Agronomy Extension Soil Fertility Home Page. Nutrient topics are listed on the left side. Simply click on a topic of interest and you can find information about that topic, including Extension publications, newsletter articles, conference proceedings and reports, presentations, and links to other related sites. Links also provide access to soil fertility decision aid tools, a photo gallery, and the ISU Soil and Plant Analysis Laboratory.

Current Topic

NITROGEN FERTILIZATION RATES FOR CORN PRODUCTION

John E. Sawyer, Professor, Department of Agronomy, Iowa State University
October 14, 2014

There has been a large change in corn grain prices this fall. How might that affect recommended nitrogen (N) fertilizer or manure-N application rates, and planning for the 2015 crop? The answer depends on more than just the price of corn, but also the price of nitrogen. It is the ratio of these prices (price ratio, where the $/lb actual N is divided by the $/bu corn; example, $0.50/lb N and $3.50/bu corn is a 0.14 price ratio). Both prices are important and influence recommended N rates as the ratio reflects the last unit of N that can be paid for by the yield increase from that N application. In Iowa, recommended rates (Maximum Return to N, MRTN) come from the Corn Nitrogen Rate Calculator (CNRC), which is the on-line tool providing rate recommendations for corn following corn and corn following soybean. The rates derived from the CNRC are adjusted for user specified N and grain prices. While a significant change in grain price may be troublesome, it may or may not affect recommended rates because of current N price. Read on.


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Iron chlorosis symptom - soybean. Photo © John E. Sawyer

Iron chlorosis symptom - soybean. Photo © John E. Sawyer

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