A Procedure to Determine in-Season Optimal N Fertilizer Using Crop Models.

Managing nitrogen (N) fertilizer is a key aspect for increasing crop yield and reducing environmental impact.  The optimal N fertilizer amount should be the rate at which the farmer’s financial return is maximized. The optimal N (Nopt) amount varies between site location and between years for the same field cropped with the same cultivar.  Soil water availability is an important parameter to consider when making decisions about the Nopt application rates. Soil water can be highly variable within a field because of variation in

rainfall, topography, and soil properties and it affects the amount of crop N uptake during the growing season.

In this study we simulated different N rates using a long-term weather record to establish a procedure to tactically (in-season) apply the optimal amount N that would increase profitability and reduce environmental impact in rainfed-maize production in the Upper Mid-west. The SALUS model was used in this study and tested with measured data.