Selecting the “Best” Yield Response Curve – How Much Does It Matter?.

Computing the economic optimum N rate (EONR) for corn yield response to N fertilizer rate is one of the fundamental first steps in designing an optimum application program for N fertilizer.  Numerous studies have examined the strengths and weaknesses of various mathematical equations for the optimal fit to measured yield – N rate response data.  However, none of these efforts have carried forward the uncertainty inherent with the estimation of the equation parameters to the final computation and reporting of the EONR.  In this paper, I examine the strengths and weaknesses of several common equations used to describe corn yield response to N rate data and show how uncertainty in the equation parameter estimates need to be considered when computing the EONR.  The resulting EONR estimates for the various response functions are then compared using experimental data to illustrate that the resulting differences in EONR from the different response functions are not as different as many researchers have concluded.