Settling the Nitrogen Rate Debate

New publication lays out an approach to N guidelines that provides more consistency between states. Compiled by staff

Published on: Aug 3, 2006

A new publication, developed jointly by soil fertility specialists from Midwest universities, illustrates a regional Corn Belt approach to nitrogen rate guidelines.

Concepts and Rationale for Regional Nitrogen Rate Guidelines for Corn was developed jointly by soil fertility specialists from the University of Illinois, Iowa State University, the University of Minnesota, The Ohio State University, Purdue University and the University of Wisconsin.

Using recent nitrogen rate trial data from multiple states, this publication illustrates a suggested approach for developing corn N rate guidelines. The approach uses an economic evaluation of N application rates, called the maximum return to N (MRTN). The goal of the regional effort was not to develop one N rate recommendation for the region, but rather to explain the science behind corn N use and fertilization requirements, and develop an approach to N guidelines that could provide more consistency between states.

The publication primarily deals with N use in rain-fed conditions, with corn following soybean and continuous corn. The publication also addresses the question of determining N rates with ever-increasing corn yields. Instead of relying on yield goal, this publication outlines an approach that uses yield increase to N application and determines maximum economic return. Nitrogen application rate is critical because it improves corn yield dramatically, but also is one of the largest corn production expenses.

Another outcome of the regional effort is a Web-based tool called the Corn Nitrogen Rate Calculator. Producers in Illinois, Iowa, Minnesota and Wisconsin can use this tool to calculate the MRTN rate, profitable N rate range, net return, percentage of maximum yield, and other information directly from N response trial databases for each respective state. The calculator is located at

Copies of the publication are available on the web through the ISU Extension Distribution Center at or by calling (515) 294-5247.