Active canopy sensors offer accurate measurements of crop growth status that have been used in real time to estimate nitrogen (N) requirements. NDVI can be used to determine the absolute amount of fertilizer requirement, or simply to distribute within the field an average rate defined by decision models using other diagnostics. The objective of this work was to evaluate the capacity of active canopy sensors to determine yield and N application requirements within a site at jointing stage (Feeks 6 or Zadoks 31), and in particular the capacity to detect non-responsive areas of the field. For this purpose a set of 6 large nitrogen response field experiments were conducted at contrasting sites where canopy readings were acquired with Cropcircle CS-45, and complimentary information (leaf area, biomass, and nitrogen absorption) was obtained.  In addition two fields were surveyed with a commercial canopy sensor (Cropscanner) and check/not-limiting plot pairs at different locations with contrasting NDVI readings were installed. Sensor readings correlated well with biophysical measurements and were good predictors of yield for treatments with and without fertilization after canopy readings. When grouping the plots by NDVI at the time of top dress, N response curves showed different optimum application rates according to NDVI readings. Sites or locations with medium NDVI presented response to larger rates of N, while sites or locations with either low or high NDVI presented response to lower rates of N. At the field level, similar trends were observed. Low NDVI areas show the greatest promise in N savings and return to variable rate technology use. Even when absolute requirements seem difficult to estimate for each location, sensors provide an objective evaluation of crop status across the field at the time of measurement that allows for the distribution of N across the field.