Evaluation of Algorithm Thresholds for Crop Canopy Sensor-Based in-Season Nitrogen Application.

The use of active crop canopy sensors for variable rate application of nitrogen (N) has been researched to the point that there are now commercialized systems being marketed to corn producers. These sensors rely on research-developed algorithms to determine the need for N application with the goal of improving N use efficiency and maintaining an economic benefit to the producer. The sensor systems have focused on applying nitrogen based on a sufficiency index derived from a well fertilized reference strip in the field. If the crop being sensed has a sufficiency index that indicates a lower value than the reference strip, nitrogen will be applied. As the index value decreases, the applied rate of N increases. However, at some point the increased yield due to N application will not pay for the added fertilizer, especially in areas with marginal plant stands or significantly stunted plants. This study evaluated economic thresholds to protect the producer from over-application of N fertilizer to a crop that will not respond to added nitrogen fertilizer. Data evaluating two threshold approaches will be presented from the 2009 and 2010 growing seasons.