Effective management of fertilizer nitrogen (N) in corn production is needed to maximize economic return for producers and control N losses that can cause environmental problems. Environmental concerns with N use in corn production are mainly focused on nitrate leaching to ground water and surface water nitrate contributions to Gulf of Mexico hypoxia. The key to improving N management to achieve economic and environmental goals is accurate selection of the optimum N rate needed for profitable production in each production unit. Many corn N response experiments have shown that optimum N rates vary widely from site to site, and substantial within-field variation in optimum N rates is expected, although little work has been done to confirm or quantify the within-field variation of optimum N rates. Variable rate N applications should have potential for applying optimum N rates to all areas of production fields with substantial spatial variation in optimum N rates. If rates of applied N can be matched to actual corn N requirements throughout production fields, the economic and environmental goals of N management could potentially be achieved to a greater extent than would be possible with a single N rate applied to the entire field.