“The fertilizer question is alive and well,” says Dr. Emerson Nafziger, professor emeritus at the University of Illinois Urbana-Champaign, in a farmdoc webinar hosted by the Illinois Corn Growers Assoc. As a specialist in crop and soil management, he, like many farmers today, has struggled to pinpoint the most economical amount of nitrogen (N) fertilizer needed for any particular crop.

“About 20 years ago, several of us met together in the Midwest and talked about the fact that we had data for N responses,” Nafziger says, “but we were wondering what we could do with it to make N recommendations come alive.”

From this question and years of data collection, Nafziger developed the MRTN, or Maximum Return to Nitrogen, which he stresses is not just an economic tool but also an agronomic one.

The MRTN is essentially a calculator in which farmers can enter expected corn prices and expected cost of N to receive data on the most profitable application of N per acre. Nafziger stresses these are guidelines, rather than recommendations.

Initial Conclusions

Data was accumulated from 7 sites in northern, central and southern Illinois on corn-on-corn acres and corn-soybean rotations over the course of 10 years.

“Part of our early observation was that the yield goal-based system that we had in place since the 1970s was starting to fall apart, and it was falling apart primarily because yield levels and the need for N were not very closely associated,” Nafziger says.

The goal-based guideline purported that expected…