Can Unmanned Aerial System-Mounted Passive Sensors be Used to Recommend Sidedress Nitrogen Rates in Corn? a Comparison Among Active and Passive Sensors.

The objectives of this research were to (i) assess the correlation between active and passive crop canopy sensors’ vegetation indices at different corn growth stages and (ii) assess sidedress variable rate nitrogen (N) recommendation accuracy of active and passive sensors compared to the agronomic optimum N rate (AONR). This study is comprised of six site-years, being conducted on 2015 and 2016 on different soil types (silt loam, loam and sandy loam) and with a range of preplant N rates. The N source was either urea-ammonium nitrate (UAN) or anhydrous ammonia (AA). Crop reflectance data was acquired using three different sensors: RapidScan (handheld, active) and Tetracam or Red-Edge (UAS-mounted, passive). Sensors were utilized over different crop stages, from V6 through R2. For all sensors, NDVI and NDRE were calculated. The treatment receiving the highest N rate in a given site-year was considered as the N-sufficient reference in order to calculate a sufficiency index, then used as an input in the algorithm for sidedress N rate determination. Data is still being collected and further results will be included in the future.