Fine-tuning N fertilization is important for improving the economic and environmental impact of corn production. Reflectance measurements with active sensors during the growing season may be useful for determining the need for additional N. Field scale experiments were established at five locations throughout Indiana with a single corn hybrid, Pioneer 34A19, sidedressed at V3 to V5 growth stage with 0, 45, 90, 135, 180, and 224 kg N/ha. Reflectance of 590 and 880 nm wavelengths from the crop canopy was determined at V11 with a Crop Circle active sensor. The ratio of reflectance at 880 nm and at 590 nm at each N rate, expressed as a percentage of the ratio at 224 kg N/ha, were highly correlated (R-squared of 0.82 – 0.92) with leaf N at silking, Minolta SPAD readings, and yield.