The nitrogen (N) supplying capacity of the soil available to support corn (Zea mays L.) production can be highly variable both among and within fields. In recent years, canopy reflectance sensing has been investigated for in-season assessment of crop N health and fertilization. Typically the procedure followed compares the crop in an area known to be non-limiting in N (called a N-rich area) to the crop in areas inadequately fertilized. Measurements from the two areas are used to calculate a relative reflectance to represent the potential need for additional N fertilizer. Putting in N rich areas or strips is often inconvenient for farmers, since this coincides with other demanding spring operations. Thus the question has been asked, is an N-rich reference needed? The objective of this study is to answer that question. A total of 16 field-scale experiments were conducted over four growing seasons (2004-2007) in three major soil areas of Missouri, USA: river alluvium, deep loess, and claypan. Multiple blocks of randomized N rate response plots traversed the length of the field. Each block consisted of 8 N treatments from 0 to 235 kg N ha^-1 on 34 kg N ha^-1 increments, top-dressed between vegetative growth stages V7 and V11. Adjacent to the response blocks, N-rich (235 kg N ha^-1) reference strips, along with strips of the usual producer practice and of candidate N algorithms were also established. These ran the full length (400 to 800 m) of the field. Crop canopy reflectance sensor measurements were obtained from the N response blocks and adjacent treatment strips at the time of top-dress N application. Grain yield was measured with a yield-monitor equipped combine. Other available data included soil electrical conductivity (EC), topographic attributes calculated from RTK-DGPS data, growing-season weather, and aerial imagery. The datasets will be examined using different processing and filtering techniques to explore if an alternative to an N-rich reference is feasible. This research is expected to provide an increased understanding of how canopy reflectance-based N recommendations can be employed to improve variable-rate fertilization on farmers’ fields.