Optical canopy sensors are an emerging technology that can serve as a useful in-season N fertilizer management tool for corn (Zea mays L.) production. The sensors provide an estimate of plant biomass and N status at the time of sensing. These growth parameters can be used to make in-season N rate adjustments and variable rate N applications. Currently, a robust and accurate algorithm to determine the appropriate N rate based on canopy sensing is need in order to improve the effectiveness of active sensors in production fields. The objective of this study is to determine the ability of optical canopy sensors to differentiate N stress in corn for adjustment of N fertilization rates.