Utilization of active canopy sensors for nitrogen fertilizer management in corn

Abstract

Identifying factors that can significantly affect optical sensor performance is important if active canopy remote sensing technology is to be used in production agriculture. The objectives of this research were to determine the effects of different lighting conditions on active sensor values, vertical depth penetration of active sensor light into a corn (Zea mays L.) canopy, and differences between canopy reflectance values from single vs. multiple active sensors units. Corn was sensed at the V10 growth stage with the GreenSeeker Green model 506 (GS-506) and Crop Circle ACS-210 (CC-210) active canopy sensors. Canopy sensing was conducted during the day and at night, and with and without artificial light. The bottom 2, 4, 6, 8, and 10 leaves of corn plants were removed and canopy sensing was conducted after each leaf removal treatment. A three-sensor CC-210 unit was used to determine differences between individual sensors and to compare means when sensor reflectance values were combined. Near-infrared (NIR) and visible (VIS) reflectance values from the CC-210 were not affected by different lighting conditions. The GS-506 generated greater reflectance values during the day, indicating the sensor measured some passive reflectance via sunlight. The GS-506 had greater vertical light penetration into the corn canopy compared to the CC-210, likely due to a more concentrated field of view. Different NIR reflectance values were found with each of the CC-210 active sensor units and with