Determining in-season corn N status variability is important to optimize N fertilizer use and economic return. Currently there are several methods available to identify in-field N variability; however these methods are often cost prohibitive, labor intensive, and destructive to the crop. One way these limitations can be overcome is to use hand-held or tractor mounted active remote sensing devices that calculate normalized difference vegetation indices (NDVI). There are several sensors commercially available that determine NDVI and studies have found that they adequately quantify N variability. The focus of this study was threefold. 1. To compare the NDVI readings of three commercially available active remote sensors when assessing N variability within irrigated corn fields. 2. To determine the ability of a ground based active remote sensors to detect previously delineated production level management zones based on corn N variability. 3. To determine the effects of environmental factors such as wind and corn row spacing on the accuracy of ground based NDVI sensors. We concluded that, depending on corn growth stage, all three units accurately quantify corn variability as affected by N fertility level. The NDVI readings collected in corn at the V12 growth stage relate well to previously delineated high and low production level management zones and that all three sensors accurately determine N variability across a wide range of environmental factors as long as these factors are constant. Active remote sensors appear to have the potential for large scale use in the field to differentiate N status of corn plants over a wide range of environmental conditions.