Since the introduction of synthetic fertilizers have increased crop yields, inaccurate fertilizer rates have been applied due to failure to recognize temporal variability. The calibration stamp technology is one method in which a producer can manage temporal variability by determining nitrogen (N) response in-season and making the suitable topdress N application. This study evaluated the use of early season N fertilizer strips (45, 90, and 135 kg N ha-1) to visually interpret N response mid-season and apply a field-based topdress N application compared to measuring in-season RI (RINDVI) using a GreenSeeker® Hand-held optical reflectance sensor. These comparisons were conducted at 10 different experimental sites across Oklahoma during the 2004-05 crop year.