Characterizing Soybean Vigor and Productivity Using Multiple Crop Canopy Sensor Readings.

Crop canopy sensors have become an effective tool to assess the crop status and to direct in-season management of several cereal grain crops; however, their utility in oilseed crops, such as soybean [Glycine max (L.) Merr.], has remained more elusive. Traditionally, crop canopy reflectance measurements are obtained at certain times during the growing season to infer physiological characteristics about the crop. The goal of this experiment was to determine if the use of sequential reflectance measurements could be used to characterize the vigor and productivity of soybean fields. Crop canopy reflectance measurements were taken from experimental sites evaluating the impact of seed and foliar inputs on soybean yield. Each experimental site was located within a soybean producer’s field. Red (R), red-edge (RE), and near infrared (NIR) measurements were recorded from each experimental plot using a RapidSCAN proximal sensor twelve times throughout the growing season. A method used by plant pathologists, the area under the disease progress curve (AUDPC), was utilized to calculate the cumulative normalized difference red-edge (NDRE) index values from early vegetative stages through R3 for each plot, hereby termed the area under the reflectance progress curve (AURPC). For each site, the top and bottom ten percent of plots by AURPC were selected to determine if the average yield was significantly different between the two groups. In five of the eight locations, plots with the higher AURPC values yielded more than the plots with the lower AURPC values (p=0.05). Although the area of each plot was small, between 0.39 ha and 0.45 ha, these results indicate that crop canopy sensors have the potential to characterize the relative yield potential of a soybean field before the critical time when foliar applications may be made at the R3 growth stage.