Here’s a review of the major optical crop sensor options:

Ag Leader OptRx. Ag Leader introduced the OptRx system for use in corn in 2010. For 2011, Ag Leader also will support its use in wheat. OptRx was developed in conjunction with Holland Scientific, for which Ag Leader is the sole worldwide distributor for production agriculture markets.

OptRx sensors measure visible and near-infrared light reflected from the crop canopy to determine a vegetative index used to set varying nitrogen application rates. The system includes boom-mounted sensors, plus a Canbus module that carries sensor data to software contained in Ag Leader’s Insight or Integra displays.

Ag Leader recommends using three OptRx sensors on booms less than 80 ft. wide. Five sensors are recommended on wider booms. Sensors retail for $3,000 each. The Canbus module retails for $1,500. The cost of a five-sensor system is $16,500, plus the cost of an Insight or Integra display, if needed. For more information, visit www.agleader.com.

Topcon CropSpec. The CropSpec sensor system, which was available on a limited basis in 2010, will have its full U.S. launch in 2011. It was developed in conjunction with Yara International, a fertilizer and industrial chemical manufacturer based in Norway.

The sensor system uses two sensors mounted on each side of the application rig cab roof to measure red and red-edge light reflecting from the crop. The sensors are mounted at a 45° to 55° angle, which allows them to take readings from several crop rows contained in roughly a 3-meter ellipse.

The two-sensor CropSpec system retails for $19,500. It interfaces with the Topcon X20 display/controller, which retails for $5,665. The company plans to add compatibility with additional Topcon displays in the future. For more information, visit www.topconpa.com.

Trimble GreenSeeker. The GreenSeeker system has been available in the Corn Belt since 2005, first from NTech Industries and from Trimble since its purchase of NTech in 2009. It was developed in conjunction with crop scientists at Oklahoma State University as an outgrowth of a related product, the WeedSeeker optical sensor weed-control system.

GreenSeeker sensors measure red and near-infrared light to assess plant vigor and determine appropriate nitrogen application rates. In addition to corn, GreenSeeker has been used for variable-rate nitrogen applications in winter and spring wheat, sorghum, canola, cotton, barley and Bermuda grass. It also has been used for variable-rate applications of growth regulators and defoliants in cotton.

Trimble recommends use of six GreenSeeker sensors for booms greater than 60 ft. and four sensors for shorter booms or side-dress rigs. It is available in two configurations: one for use directly with the Trimble FMX display, and a second for use with the Trimble Nomad handheld computer, which can interface with John Deere GreenStar monitors and various controllers, including Raven controllers ranging from the Raven 440 to the Viper Pro.

GreenSeeker FMX configurations retail for $13,495 for six sensors, and $9,995 for four sensors. Configurations including the Nomad handheld computer retail for $19,995 and $16,495 for six- and four-sensor systems. For more information, visit www.trimble.com/agriculture.