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Gary Wagner studies a yield map Lon Tonneson
GOOD MAPS: Gary Wagner studies a yield map of one of his fields

Producing better yield maps with careful calibration

Precision ag farmer Gary Wagner checks and rechecks his sensors to ensure accuracy.

Gary Wagner is keenly aware of the computer age axiom “garbage in equals garbage out,” especially when it comes to yield maps. The Crookston, Minn., farmer has been using precision farming technology for 29 years and has even taught a college class on the topic at the University of Minnesota Crookston.

Wagner takes extra time at the start of harvest to calibrate his family’s AgLeader combine yield monitors.

“If you want to have yield maps that you can actually use to make decisions, the data needs to be accurate,” he says.

Wagner and his brothers, Wayne and Daryl, and his son-in-law, Jason Bailey, operate Wagner Acres, of Crookston, Minn., together. They grow sugarbeets, wheat, soybeans, sunflowers and corn.

On the first day of harvesting any of their grain or oilseed crops, they fill the hopper three to six times with at least 3,000 to 6000 pounds of grain weigh the grain each time with a grain cart scale. They operate the combines at different speeds each time, usually between 2 and 6 mph, to calibrate the yield monitors across the full grain of grain flow they expect to see. At the same time, they calibrate the combines’ grain moisture and temperature sensors. They also calibrate for zero-flow combine vibration.

During harvest, if weather or crop conditions change significantly, Wagner rechecks the sensors.

“Normally if we do a good job calibrating the first day the need for additional calibration loads is not necessary,” he says. “We can get our yield monitors to within plus or minus 3% of the scale.”

Why calibration is so important

It’s important to the Wagners to have accurate estimates of the yield across a range of combining speeds because Wagner uses yield maps to help create variable rate fertilizer and seeding prescriptions. He also frequently compares variety and hybrid and crop input performance across management zones.

If you don’t calibrate the monitors for the full range of operating speeds, you’ll see false differences between the yields, he says.

For example, if a farmer only calibrates his or her monitor at one speed, and if he or she speeds up to finish a field before nightfall, a rain shower or at the end of the season, then the yield values will be overestimated compared to the single calibrated values.

The same thing happens at night or in dusty conditions. Normally in these conditions the combine will travel slower, and if the yield sensor is only calibrated at one speed (for accuracy) a 10% yield reduction can be noticed. Then the next day, when traveling at the single calibrated speed the yield values will return to normal.

If you run two combines and they weren’t calibrated properly or are being operated at different speeds, they may show yield differences where none really existed.

“There is no easy button for calibration,” Wagner says, “but it is worth doing it right. I have to be able to believe my yield maps.”

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