Precision agriculture technologies are an integral part of many operations in Iowa corn production. Active canopy sensors have been developed as a tool to determine plant N stress deficiency and provide on-the-go decisions for implementing variable rate N application. The objectives of this study were to assess N deficiency stress levels at the mid-vegetative corn growth stages with active canopy sensors, calibrate active sensors and associated canopy indices, and develop N rate algorithms that can be used to determine variable rate N fertilization.