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Mosaic with A Meaning
New Technology Records Yield Variations in the Field

Top Producer
Written By:  Larry Reichenberger
December 1993 pgs. 36-37

Gary and Wayne Wagner with their laptop computer used in determining yield
Gary (left) and Wayne (right) display their laptop computer they use in determining yield.

In what may be the ultimate modern art, some farmers are suing high-tech flow sensors, laptop computers and a space-age navigational system to paint pictures of their fields.  More precisely, the art work depicts yield variation mapped while harvesting those fields. As with all good art, there’s meaning to every shape and color of the mosaic.

Gary, Wayne and Daryl Wagner drew yield maps for 1,200 acres of their Red River Valley farmland as they harvested wheat this fall.  The brothers, who operate AWG Farms Inc., in Crookston, MN, were amazed to see yields range from 29 to 80 bu. an acre on fields they thought were fairly uniform.

Yields in this 160-acre field were checked roughly every second and the results plotted according to their location.  The resulting data were color-coded to reveal yield-variation patterns ranging from below 30 bu. an acre (red) to more than 50 bu. acre (green).

AWG Farms Wheat Yield Map

“We’ve never imagined we had so much variation,” says Gary.  “Yields changed 20 to 25 bu. an acre in wheat that looked uniform from the combine. Now we’ll go back to the low-yield areas looking for low fertility, compaction and poor drainage.”

The Wagners worked with Ted Macy of Application Mapping in Frankfort, IL (815-469-7504), to assemble their mapping system.  The main component is the Yield Monitor 2000.  It measures yields on the go by sensing the strain on a pressure plate in the top of the clan grain elevator.  The monitor corrects for moisture and logs yield data to a laptop computer (miniumum 286) with Macy’s MapSight software.  At the same time, a receiver logs location data from satellites in orbit as part of the global positioning system (GPS).

“The monitor and receiver log yield and location of data on the computer every second,” explains Macy.  “This information is stored on a data card that is then plugged into a mapping program back in the office to generate the yield map.”

Price Tag. The Wagners’ system cost roughly $8,000, including a roving GPS receiver.  This does not include a differential GPS base station, which most farmers won’t need.  The Department of Defense, which operates the GPS system, puts an error factor in the satellite signals. To restore accuracy, a differential receiver and radio link are needed.  Because the Wagners aren’t within range of an operating differential GPS tower, they installed a tower a their shop.  However, subscriber networks are springing up around the country to provide differential signals for a fee- generally around $500 a year.

“With the differential tower, location was accurate to within 10’ or 15’,” says Gary. “The biggest error with the yield monitor was 1.2%, so the entire system was extremely precise.”

The Wagners are convinced the system will pay. Their main cash crop is sugar beets, whose quality is easily affected by soil conditions, including fertility.  Discounts for poor-quality sugar beets run up to $200 an acre.

Telltale. “We hope to use wheat as an indicator crop to point out low- and high- yielding areas of the field before we plant sugar beets,” says Gary. “This will help us balance fertility in the field and improve the quality of the sugar beet crop.”

Even in wheat, Gary sees payback potential. “An obvious way it will pay is in weed control,” he says. “Wild oats are a major problem for us.  Typically, chemical control costs us $13 an acre.  However, we can log areas with wild oats as we harvest. Using the field map and a GPS receiver, we can go back and treat only the weedy areas prior to seeding the next crop.  On one 80-acre filed we’ll only have to treat 12 acres. That will save $884 in chemical costs in the field alone.”

Gary also thinks he can either increase yields or decrease costs by basing fertilizer rates on the yield map.  Researcher are only beginning to assess the economics of variable application. In a study of three fields in Missouri it raised gross returns by $40.89, $16.38 and $9.14 an acre.  It increased costs by $10 to $15 an acre, so only one situation was clearly profitable.

Still, yield mapping may play a major role in making variable application more affordable. “Previously, we've had to take a huge number of soil samples to get an accurate map of variability in a field,” say Kansas State agronomist John Havlin.  “Soil sampling became a major part of the overall expense. However, with a yield map, we should be able to test only the areas where yield variations occur.  This could dramatically lower the cost of variable-rate systems.”

Gary Wagner and the Yield Monitor 2000

The Yield Monitor 2000 continuously measures and displays crop yield, moisture, combine speed, grain flow and acres per hour.

The Yield Monitor 2000, which the Wagners used to develop the map, can be installed without mapping capabilities. “We’ve got more than 100 units out, and 15 or 20 of them operate with the GPS mapping capability,” says inventor Al Myers of Ag Leader Technology, Ames, Iowa (515-232-5363). “Most users simply use it for yield information while harvesting.  It’s especially valuable this year to determine the yield impact of ponded areas and delayed maturity.”

The monitor sell for $2,995. The optional moisture sensor adds another $395.  Myers is working on a new version of the unit that reads and records GPS data itself, so the laptop computer now required for mapping can be eliminated.  “With our new unit, we’ll record all the information on a data card that farmers can take to their crop consultant, fertilizer dealer or their own office computer to print out and analyze,” says Myers.

Micro-Trak, Mankato, MN (800-328-9613), is also marketing a new yield monitor. The company purchased the Harvestyield monitor, which was marketed last year by Dawn Equipment, then solved some electrical problems and reintroduced it last summer. It sell for $1,250.

The Harvestyield monitor is not available with a moisture sensor and can’t be teamed with a GPS receiver for yield mapping. For that, Micro-Trak is developing a new Grain-Trak yield monitor.

“The Grain-Trak monitor will be available next season,” says Scott Veldman, president of Micro-Trak.  “It will sell for $2,300 with moisture sensors. An optical Data-Trak interface ($575) will provide the GPS hookup needed for yield mapping.”

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