Spot-drop Biosensor-based Spatial Nitrogen Management

Abstract. Rain-fed corn fields do not behave the same every year. The swing interactions can flip which parts of a field perform best, making nitrogen (N) decisions risky. To make N decisions more responsive to what the crop needs, we evaluated a Spot-drop biosensor approach that uses the crop as the “sensor.” With Spot-drop, small N-rich georeferenced spots are applied at planting. Remote sensing compares the crops inside these N-rich spots to the surrounding crop. That difference is used to generate zone-specific, in-season N rate recommendations, helping match N rates to within-field demand instead of relying only on pre-season expectations. We tested this approach in on-farm precision trials across 116 acres of rain-fed corn in SD, comparing Spot-drop recommendations to a flat-rate strategy and a conventional variable-rate prescription. Crop response in the N-rich spots varied across four field zones, with the strongest NDVI response in Zone 1 and the weakest in Zone 4, showing that N need and yield potential were not uniform across the field. Across zones, higher N rates generally increased grain yield, while lower N rates improved Nitrogen Use Efficiency (NUE). Spot-drop–guided variable-rate N improved corn yield by up to 20%, demonstrating strong potential to refine in-season N decisions, boost returns, and reduce unnecessary N losses.