Precision agriculture technologies are an integral part of many crop production operations. However, implementation for N application has lagged, primarily due to lack of a viable system for variable N rate decisions. Active canopy sensors have been developed as a tool to determine plant N stress deficiency and provide an on-the-go decision for implementing variable rate. There are two general approaches. One is to conduct canopy sensing each year, with a reduced N rate applied preplant, at planting, or early sidedress and then sensing at mid-vegetative growth to determine additional application need. A second is to conduct sensing only if conditions result in N loss from the primary N application, or other factors change expected crop requirements. Both approaches could address variable N fertilization and seasonal conditions.