With both nitrogen and diesel fuel costs at near record highs, row crop farmers from coast to coast are looking for ways to cut fertilizer costs without jeopardizing the yield and quality potential of their crop.

In a cooperative project with NRCS, Virginia Tech researchers have worked with Greenseeker, a high tech system that senses color variations by reading chlorophyll levels in plant tissue. In tests at six sites in Virginia, Greenseeker use has produced yields comparable to standard applications based on soil and tissue sampling.

When the six sensors on the Greenseeker RT200 pass over a crop, it sends down two rays of light — one infra-red and one near infra-red. The infra-red light reads chlorophyll by sending down a thin band of light that reflects back up. The greener the tissue is, the less light is reflected back to the sensor, because the green absorbs the red light.

The near infra-red light measures the energy vibration inside a cell wall, or biomass. The color and thickness of a crop that is read by the six sensors across a 60-foot spray boom, provides an average of data than can determine how much fertilizer goes out every 20 feet.

Virginia Tech Extension Specialist Paul Davis, who demonstrated the Greenseeker RT200 at a recent field day in New Kent, Va., says the equipment is not quite user friendly enough to be widely adapted by farmers. “It’s close, Davis says, it’s getting there and it will be a great cost-saving tool when it is refined just a little.”

Using the Greenseeker on wheat, nitrogen application was compared to standard application. Standard application is based on 30 pounds of N at planting and coming back at Growth Stage 25 and doing a tiller count. If the stand is not adequate, 60 pounds of nitrogen is used. If adequate tillers are evident, 30-40 pounds are used to keep the plant going until Growth Stage 30. At Growth Stage 30, tissue samples are analyzed for percent nitrogen in the plant. Once the tissue sample comes back, precise amounts of nitrogen needed can be determined.

The algorithm used to develop the spray program used by Greenseeker in the Virginia tests was based on standard nitrogen use numbers as determined by a combination of visual and laboratory analysis of the plant’s needs.

The Greenseeker system comes with six sensors, a modem that averages data from the six sensors, a computer that has the equation, or algorithm, which goes to the spray control system. The computer has to compare the needed rate to something, so a test strip must be used to provide a comparison for the system.

Each year a new test strip must be left to give the computer an accurate reading of the current fertility level of the field. Even different varieties need their own test strip. Even if the same variety is grown year after year, a new test strip is required to keep the data current, which allows the Greenseeker system to make the most accurate nitrogen application possible to allow the plant the optimum chance to produce up to its genetic potential.

In field operation, the Greenseeker system will apply more nitrogen to areas of a field with greater yield potential and less fertilizer to weaker areas of a field. The system will apply a maximum amount of fertilizer, based on the amount used in the test strip. A minimum amount can also be set, providing a range within which the system will stay.

In the New Kent, Va., tests, at Growth Stage 25, the researchers added 90 pounds, instead of 40 pounds. The sensor then sets the sprayer to look like the test strip. Readings from the test strips can be made by the computer on-board the tractor, or by a hand held computer. The readings are presented in NDVI, or normalized different vegetative index.

The NDVI ratings can be programmed into the onboard computer, which drives the sprayer application. On smaller tractors, with 60-foot booms, optimum tractor speed is 7-8 miles per hour. On bigger booms, 90- feet or more, tractor speeds may be 12-15 miles per hour without losing efficiency.

Using a Raven controller, the Virginia researchers were able to make changes in fertilizer application approximately every 20 feet. “Every time the NDVI ratings change, the system beeps, and there is no silencer,” Davis jokingly told the field day crowd. “When the NVDI ratings remain fairly constant, there is no beep, or change in nitrogen rates,” the Virginia Extension leader explains.

“Last year was a real learning experience for us,” Davis says. “It sometimes took 6-7 days to get the information from the field, to the lab on the Eastern Shore and back to us, and the wheat was growing so fast, we couldn’t always keep up with the changes,” the Extension Leader explains. For the 2006 season, NTech Industries, manufacturers of the Greenseeker equipment will send a system with the Virginia wheat algorithm already encoded, which should make the system even more efficient, Davis adds.

e-mail: rroberson@farmpress.com