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Corn+Soybean Digest

Corn Nitrogen Rate Calculator Is Online

Corn producers can calculate the economic return to nitrogen (N) application with different N and corn prices using a new regional Web-based tool located at the Iowa State University Extension Agronomy Web site.

The Corn Nitrogen Rate Calculator, online at, follows a newly developed regional approach for determining corn N rate guidelines that is being implemented in several Corn Belt states. The Web site includes an animated demonstration of the calculator.

University soil fertility specialists from the Corn Belt states began discussions in 2004 regarding N rates for corn production, according to John Sawyer, ISU Extension soil fertility specialist.

"We were looking at differences in methods for determining suggested N rates across states, misperceptions regarding N rate guidelines, concerns about application rates as corn yields have climbed to historic levels and current high N fertilizer prices," Sawyer says. Results of those discussions included the development of a regional approach to N rate guidelines and a method for determining the most profitable fertilizer N rates for corn production in states across the Corn Belt.

The Web site calculates the net economic return to N application and finds the maximum return to N (MRTN) rate directly from recent research data. "MRTN is the regional approach suggested for developing corn N rate guidelines in individual states," Sawyer says.

The Web site includes N rate trial data for four states (Illinois, Iowa, Minnesota and Wisconsin) that had an adequate number of research trials available for corn following soybean and corn following corn. These trials were conducted with spring, sidedress or split preplant/sidedress applied N, and sites were not irrigated.

Using the online calculator, producers can calculate returns for one set of N fertilizer and corn grain prices or multiple prices for the state and rotation they are interested in. An advantage is that prices can be tailored to a producer's specific N fertilizer purchase and corn grain marketing. The results of calculations are provided in a table and graphs.

The Web site calculates the MRTN rate in lb. N/acre and net return to N in dollars/acre. Graphs also show the distribution of economic optimum N rates for the N response trials and the relationship between yield and economic optimum rate.

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