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New handheld GreenSeeker sensor debuts

By Doug Rich

GREENSEEKER—The newest handheld GreenSeeker sensor is now available from Trimble. The unit is about the size and weight of a large flashlight. (Journal photo by Doug Rich.)

Farmers in southeast Kansas had an opportunity recently to learn about the latest improvements in GreenSeeker technology at an educational meeting, sponsored by Record Harvest.

The new GreenSeeker sensor really is a handheld unit. The old handheld version was about 51 inches long and with the complete case weighed in at 38 pounds. The new unit is about the size and weight of a large flashlight.

The size was not the only thing that was reduced. The new handheld GreenSeeker sensor costs $500 compared to $5,000 for the old unit. Trimble began offering the new, smaller sensors to customers in August.

GreenSeeker technology is not new. The National Aeronautics and Space Administration first introduced it in 1972 on their Landsat 1 satellite. Trimble engineers took the technology off the satellite and put it on farmer's sprayers and now they have put in to farmer's hands.

Russ Linhart, Trimble sales manager for GreenSeeker, said the senor uses light-emitting diodes to generate red and near-infrared light. This light reflects off the crop and is measured by a photodiode in the front of the senor head. Basically, healthy plants absorb more red light and reflect more NIR than do unhealthy plants. The amount of reflection is converted to a number that can be managed with the Normalized Difference Vegetative Index.

GreenSeeker technology can be used with a variety of crops but it is very useful in determining when and if to topdress winter wheat. The system begins by planting a nitrogen rich strip across the field to serve as a reference strip. David Mengel, Kansas State University professor of agronomy, suggests making this strip at least 125 percent of the normal rate, point it at the reference strip and take a reading. Then using the same handle unit, he takes numerous readings across the rest of the field. Steve Cubbage, president of Record Harvest, said the location and number of readings taken across the field would be like taking soil samples in a grid pattern.

Brent Rendel, a farmer from Miami, Okla., has been using intensive nitrogen management for eight years. In 2005 he put out three different levels of nitrogen rich strips in a field on his farm as part of an Oklahoma State University demonstration. A visual observation of the field showed that no more nitrogen was needed.

Rendel said his local County Extension agent had just learned how to use the GreenSeeker system so he had him come out two weeks later and use it on the same field. They got the exact same results. No more nitrogen was needed on that field.

All the other fields on his farm received 30 pounds of nitrogen in a topdress application in addition to the 75 pounds he put down at planting. At harvest that year the farm average was 33 bushels per acre. The field that received no topdress application yielded 33.9 bushels per acre.

"If you go to this system you need to get out of the mode of bushels per acre and get into the mode of profit per acre," Rendel said. "Sometimes lowering your nitrogen will lower your yield but it will rarely lower your profit."

Currently Rendel puts out 25 pounds of nitrogen at planting and puts nitrogen rich strips in each field prior to emergence. These strips get at least 150 pounds of nitrogen. Rendel said it is essential to mark these strips with a flag and write down where they are located in the field. Then he uses a handheld GreenSeeker unit to monitor NDVI readings beginning at growing degree-day 80. Finally he topdresses the crop, using a variable rate sprayer, according to the readings from his GreenSeeker sensor.

"If you are growing wheat and you are not using a sensor based system of some kind then you are losing money," Rendel said. "It is not an option that we farmers start using nitrogen more efficiently."

For more information you can go to or

Doug Rich can be reached by phone at 785-749-5304 or by email at

Date: 10/29/2012


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