The best way to find out if a crop has enough nitrogen may be to simply ask it. Light reflectance is the language to use - infrared and near-infrared light reflected by plant leaves are measures of their nitrogen status. Now, two new optical sensing systems are available that allow farmers and researchers to tune in to the crop's response.

This season, the GreenSeeker optical sensing and application system, introduced in 2003, offers a more economical, low-resolution model. The RT200 features sensors mounted at wider intervals on the spray boom than the 3-foot spacing previously used on the RT500 model. The system connects to a standard spray controller to apply nitrogen at variable rates as it moves through the field.

Equipping a 60-foot boom with the RT200 GreenSeeker system costs $12,000 to $15,000.

Nitrogen savings add up

The GreenSeeker system allows growers to make a midseason determination of additional nitrogen requirements. First introduced for use in wheat, field data from Oklahoma and North Dakota show increased revenue of $8 to $10 per acre - generally because total nitrogen rates are reduced without significant yield loss.

Last year, researchers at Oklahoma State University found the system doubled the efficiency of nitrogen utilization compared to flat-rate preplant and sidedress nitrogen applications.

"The unit was also used on 800 acres of corn in Iowa, Minnesota, and Illinois," says Ted Mayfield, vice president of NTech Industries, Ukiah, California. "On average, those growers showed a revenue increase of $18.25 per acre."

In another series of on-farm tests, USDA-ARS researcher Newell Kitchen of Columbia, Missouri, used the GreenSeeker in cooperation with seven farmers. "In some cases we found dramatic nitrogen savings - up to 90 pounds per acre in one field. On average, we found nitrogen savings of 35 pounds per acre and increased revenue of $4 to $5 per acre," he says.

A new sensor in the field

The Crop Circle unit, from Holland Scientific, Lincoln, Nebraska, is a new plant canopy reflectance sensor. One or more of the units can be mounted to virtually any vehicle to sense the biomass of a crop canopy while driving through the field.

"For nitrogen application work, we suggest four to six sensors on a 12- to 16-row sidedress unit," explains company representative Kyle Holland. "This system could be put on an existing sprayer for $5,000 to $10,000."

Holland says the Crop Circle unit has been used primarily in the turf industry. This season, researchers in Nebraska, Iowa, and Missouri will be using it for mapping and variable-rate nitrogen application in corn.

Learn more:

NTech Industries Phone: 707/467-3747 Web: www.ntechindustries.com

Holland Scientific Phone: 402/488-1226 Web: www.hollandscientific.com

Photo courtesy of NTech Industries. The GreenSeeker optical sensor uses reflected infrared and near-infrared light to gauge a corn plant's size and color for determining its nitrogen needs.