Crop Sensors to Control Variable-Rate N Applications: Five Years of On-Farm Demonstrations.

Optimal N fertilizer rate often varies widely from year to year, field to field, and place to place within a field. Site-specific N management is needed to meet crop needs without over-fertilizing. Crop sensors are an option for site-specific N management that potentially can account for year-specific factors (weather, management). From 2004-2008 we have conducted on-farm demonstrations of sensor-guided N applications in 92 fields. We had good replicated comparisons of sensor-guided variable-rate N to the producer’s normal rate in 55 of these fields. Both treatments were applied at the same time at growth stages ranging from V6 to V16. From 2004 to 2007, the two systems produced the same average yield but sensor-based N management saved 23 lb N/acre. In 2008, an unusually wet year, sensors recommended an average of 12 lb N/acre more than the producer’s rate and produced an additional 8.5 bu/acre. Crop sensors show promise to develop into a profitable and environmentally beneficial system for N rate decisions.