The advantages of using a crop model to select VRN across a field lays in the fact that N fertilizer dynamic is highly affected by other factors rather than just soil N or yield goal. To tackle the complexity of the problem, a systems approach is necessary to understand, simulate and predict the impact of N fertilizer application over space and time on crop yield. Furthermore, this study confirms that N response is field and season specific and can vary within a field. Side-by-side comparisons illustrated how much of the variability was due to inherent soil and weather conditions, versus the amount of N applied.