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Nitrogen Use: It's Not Your Grandfather's Corn

John Sawyer, Professor, Department of Agronomy, Iowa State University
February 8, 2018

Adequate plant available nitrogen (N) is a requirement for high yielding corn. Nitrogen fertilizer or manure is applied to supplement N supplied by the soil system. Fertilization rates are derived from on-farm research trials, and in Iowa suggested economic optimum N rates [Maximum Return To Nitrogen (MRTN) and most profitable N rate range] are provided through the online Corn Nitrogen Rate Calculator and the Iowa State University Extension and Outreach publication "Nitrogen Use in Iowa Corn Production".

Corn yields have increased substantially in Iowa over time, from around 40 bu/acre through 1940 to now around 200 bu/acre (statewide averages). As yield goals were used for a long time to determine N applications (ex. yield goal bu/acre times a factor), many people still expect the current high corn yields to require concurrent high N fertilizer application rates. However, suggested MRTN rates provided by the Corn Nitrogen Rate Calculator are not based on yield goals, but instead recent research trials that measure yield increase to applied N. Not using yield level (goal) in N rate determination leads many people to believe that rate guidelines are too low to support the current high yields.

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