A prototype sensor which used near infrared (NIR) reflectance techniques to determine the organic matter content of the surface layer of soil was developed and was tested both in the laboratory and in the field. Laboratory predictions yielded an r² of 0.89 and a standard error of prediction of 0.23% organic carbon (0.40% organic matter) with 30 representative Illinois soils. Limited in-furrow field operation of the sensor produced a much higher standard error (0.53% organic carbon), due to the movement of the soil past the sensor as scanning was accomplished. Although improvements in sample presentation techniques are required before the sensor can be used in real-time field operation, the current configuration could provide rapid, on-site organic matter determination for mapping and subsequent application rate control using a positioning system.