A hand-held greenseeker device that measures nitrogen levels of field crops could come in handy this spring, should fertilizer be in short supply in the United States.

The GreenSeeker crop sensor , manufactured by Trimble Navigation , uses red and infrared light to evaluate general crop health. Farmers can enter the sensor’s digital reading into an online nitrogen rate calculator to determine the nitrogen needs of specific areas of their fields.

The device is available for purchase through SpraySmarter.com. Testing conducted by Oklahoma State University researchers, who helped develop the technology with Trimble, found that GreenSeeker saves farmers about $10 per acre in unnecessary nitrogen applications and/or increased yields.

“This is what I refer to as a gateway technology,” said Brian Arnall, a soil nutrient specialist at OSU and a member of the development team. “This is going to lead producers from the hand-held sensor to variable rate technologies. It’s the light bar technology leading to auto steer.”

Weighing 11 ounces with its rechargeable battery, GreenSeeker is smaller and lighter than a hand-held vacuum cleaner. As they walk through cropfields farmers aim the sensor on the bottom of the device at plants and press the trigger. Within moments a reading between 0.00 and 0.99 appears on a display screen. The number is based on the Normalized Difference Vegetation Index (NDVI), a table used to determine plant photosynthetic activity, or “greenness,” through its light reflectivity.

“One of the things NDVI represents is the ability of a crop to respond to nitrogen,” said Micah Eidem, Trimble’s marketing manager. “One of the things we ship with every GreenSeeker is a fertilization estimation chart. That chart will walk you through the process of using the device for crops that will respond to additional nitrogen application.

“For instance, with corn production a lot of folks are looking at secondary applications of nitrogen. This device is able to look at a nitrogen-rich strip, measure the value of that strip and then take several samples throughout the field to assess what additional nitrogen is needed for crops to perform at their best level.”

Trimble also makes a spray boom-mounted GreenSeeker crop sensor system. That system can be used with most existing rate control systems and in any weather condition. It sells for around $20,000.

Farmers could find an immediate use for GreenSeeker should nitrogen supplies be limited this spring. Industry experts say the combination of a brutal winter that stalled grain traffic and rising transportation needs within the booming U.S. oil industry have slowed rail and river barge nitrogen shipments.

Nitrogen shortages are not expected to be severe but could force farmers to change their fertilization strategies.