Comparing actual N rate responses to the N rate calculator (MRTN) approach to setting N rates (2014-2017)

Emerson Nafziger, University of Illinois, and Dan Schaefer, IFCA

The following slides show the actual yield responses to N rate in on-farm trials for each year and by previous crop – corn or soybean. “Optimum” symbols (Δ) on each response curve are where the last amount of N just paid for itself in that trial. The MRTN symbols (ο) are at the N rate (and yield) produced by the N rate calculator version for that year for the appropriate region (north, central, south) in Illinois. We used typical corn and N prices for each year.

Optimum N rates from trials in years or sites with more N loss tend to be higher than MRTN rates, while in years with less N loss, optimum N rates tend to be lower than MRTN rates. The “return to N” is the price of corn times yield minus the N rate times N price. The MRTN is based on a large set of data over years, so is the “best guess” N rate.  This research is funded by NREC.