Optical sensing marketers say the key benefit of their technology in corn and wheat is that it makes it possible to apply varying rates of nitrogen across a field by measuring actual crop needs. The goal is to optimize yield by using only as much nitrogen as is needed, benefiting the pocketbook and the environment. 

They say that sensor systems address a reality that a growing cadre of university fertility scientists has emphasized in recent years: It’s virtually impossible to predict the amount of nitrogen that will be released by soils during the growing season, not to mention predicting in-season nitrogen losses. So it’s difficult to know how much supplemental nitrogen to apply. Differing soil types, organic matter levels, and other variables compound the challenge by releasing varying amounts of nitrogen across individual fields.

“Fields that have variations in organic matter and high and low areas can really benefit from variable-rate nitrogen application,” says Roger Zielke, product manager for Ag Leader’s OptRx crop sensor system. “There is a lot of money being left on the table with uniform application rates.”

Whether mounted on farm machinery, airplanes or satellites, optical sensors work roughly the same way to measure a crop’s nitrogen needs.

In ground-based systems, for example, crop sensors shoot a beam of light at the growing crop, then take ongoing readings of specific light wavelengths that bounce back. The reflected light measures crop vigor associated with variations in green plant color. This correlates with nitrogen status and the crop’s yield potential. An on-board computer then interprets the reflected light readings to adjust nitrogen rates in real time.

Aerial systems work similarly. But since they rely on sunlight, they can’t assess crops when there’s cloud cover.