Each spring, a crop is planted down on the farm operated by Hydro Agri. And each fall, along with the produce, researchers reap data on the effectiveness of various fertilizer materials. While these materials optimize the crop yield, the harvest of scientific data is refined by a tractor-mounted spectrometer system that directs the distribution of materials where the crop needs them most. Agriculture is sprouting a new crop of applications for reflectance sensors such as this one conceived by Hydro Agri and integrated by tec5 GmbH, both of Germany. The cab-mounted sensor uses reflected visible and infrared light to measure chlorophyll content in the crop and to efficiently dispense fertilizer. Courtesy of Hydro Agri. The N-Sensor system, designed and integrated in less than two years by tec5 GmbH in Oberursel, actually incorporates two spectrometers. One sensor scans each forward and rear diagonal from the tractor, while the other stares upward to measure and reference irradiance. Each sensor is a standard industrial unit manufactured by Carl Zeiss Jena GmbH with 256 pixels detecting reflectance in a 3- to 4-nm range between the visible and near-infrared of the spectrum. The optical data from each sensor are streamed via optical fibers into an onboard computer, which derives the chlorophyll content of the crop and signals the spreader to drop more or less fertilizer. The system also integrates differential global positioning satellite technology to create a map of distribution patterns for later reference. "Previous methods enabled a uniform application of fertilizer, which was not always the most efficient approach," explained Stefan Reusch, a researcher at Hydro Agri's research institute. "The optical device allows us to use the same amount of fertilizer, but just by redistributing it over the field more efficiently, we get more use out of the same amount." Easy calibration In earlier iterations, the sensors dangled on a boom stretching in front of the vehicle and required calibration prior to scanning each new field. The current prototype has a weatherproof housing about 3 m above the field atop the tractor cab. Aimed at the crop, the system collects data in a 13-m-wide swath. To use the N-Sensor that is now being introduced in US agricultural markets, farmers calibrate it simply by entering the crop variety they wish to analyze and the crop's current growth stage.