Route 1: Yield Monitor Secrets

July 28, 2008 07:00 PM

Your yield monitor can build a road map to higher yields or it can be an expensive cab ornament, producing about as much useful information as a TV sitcom. The difference hinges on understanding a handful of basic facts about monitors.

Assuming you own a monitor capable of creating a good yield map, calibration is critical. "If you don't do a good job of calibration, a yield monitor is kind of useless,” says Dennis Noland, Blue Mound, Ill., farmer. "Your yield map may be pretty, but the picture won't tell you much. With a good map, you'll have clear spatial definition. You'll see that yields line up with factors like soil type and drainage.”

Sharp definition lets you define management zones—which lets you start taking advantage of variable-rate technology, leading to more efficient use of inputs and higher yields. You can overlay your yield maps with other tools like a Normalized Difference Vegetation Index (NDVI) images for even greater precision.

Not all yield monitors are created equal. Some can do a good job of recording total bushels but not as good a job of building spatially accurate yield maps required for precision agriculture.

Here are several principles, courtesy of Farm Journal Field Agronomist Ken Ferrie, you must understand.

The road to accuracy starts with pre-season maintenance. Inspect your clean grain elevator chain and the pressure plate of your monitor, where yield sensing takes place. "Check the clearance between the paddle and the pressure plate,” Ferrie advises. "Pull the pressure sensor out, and check the plate for wear. If it is thin, it might need to be replaced.”

"Check the tightness of the clean grain elevator chain,” Ferrie continues. "If the chain is too loose, it could hit the pressure plate. Also look at the paddles; if a rivet comes out, the paddle can hit the pressure plate.”
Turn the machine on, and make sure the monitor is working. Rodents may have chewed through a wire.

Now that everything is working, clear out last year's data. Enter any new field names or numbers. That will help you keep information labeled and organized when you go to the field—and it is easier to do at your desk.

Decide in advance where you're going to calibrate. "A very important part of calibration is finding the right spot to do it,” Ferrie says. "You need an area in a field that yields uniformly because you are going to simulate different yield levels by varying the combine speed. Look for a spot where the yield is uniform and you can harvest 4,000 lb. to 6,000 lb. of grain. Avoid wet spots and hills.”

You can do this planning well before harvest season. "Use past yield maps to find areas where yield has been consistently uniform from year to year,” Ferrie says. "Pick uniform areas in as many fields as possible.

If it's your first season to use a yield monitor, recall past yields and field scouting to find a calibration area. You may need to put in a headland with your combine, in the middle of the field, to get to a uniform section.

The calibration procedure varies with each brand of monitor, so you'll want to read your operator's manual or the help pages. Prior to harvest, you must calibrate temperature, distance and vibration and inspect the moisture sensor. You can set the header stop height and check for software updates.

"With Ag Leader, Case IH AFS or Kinze Vision System monitors, your objective is to ‘train' the monitor for different grain flow rates,” Ferrie says. "The range of rates is based on the anticipated yield range. If you think your best corn will yield 240 bu. per acre and your poorest corn 90 bu. per acre, you want to calibrate for yields in between. Break the yield range into five equal segments.”

Because you're harvesting in an area with uniform yield, varying the combine speed will simulate different yields of grain. "Push the combine at its highest practical speed to find out how fast you can harvest in good conditions,” Ferrie says. "Then, back down the speed in equal increments based on the range of yields you're trying to cover.”

Harvest a strip at each of the five selected speeds; weigh the grain and input the amount into the monitor. After five trips, tell the monitor to calibrate. Harvesting at five different speeds will keep the monitor more accurate later, if you have to slow down to cross a waterway, unload on the go or power up to climb a hill.

"Failing to calibrate at five speeds is a common mistake with users of Ag Leader, Case IH AFS and Kinze Vision System monitors,” Ferrie says. "As soon as you get outside that one flow range, your yield map will no longer be as accurate.”

Another common mistake is to harvest a truck load of grain, rather than one field pass. "The separator empties out and loads back up each time you turn on the headland, adding possible error to the data,” Ferrie says. "You want to harvest the same weight of grain each load, varying only the speed.”

Your calibration will be good until the moisture content of the grain changes by about five percentage points. Then, you will need to calibrate again (which is a reason to pick out calibration areas in multiple fields).

"When you recalibrate, select a different grain type,” Ferrie says. "If you don't, the Ag Leader, Case IH AFS and Kinze Vision System monitor will recalibrate everything you've already harvested under that grain type, and you'll wind up with distorted data.”

Put it into practice. Illinois farmer Noland summarizes the calibration process: "We harvest five loads of one pass each, at different speeds, in a ¼-mile field, where the yield is uniform. We start with the high-speed, high-flow calibration load, which helps us know what our combine can actually handle. Then we reduce our speed by 1 mph for each load after that.

"If the corn gets drier, we calibrate again. It takes a little time, but it's not too bad once you get the system down.

"We started out hauling each hopper load to the elevator to get the weight,” Noland adds. "Last year, we had access to a weigh wagon. Last spring, we bought a seed tender with a scale, so now we will use that.”

John Deere's GreenStar monitor differs from Ag Leader in that you only enter two flow rates when you calibrate. "A lot of farmers only calibrate at one flow rate, which produces a lower-quality yield map,” Ferrie says.

With GreenStar monitors, Ferrie suggests users fine-tune their calibration factor. Harvest three loads at typical groundspeed. Record the calibration factor for each load, take the average and input it into the monitor. Then, harvest three loads at half speed. Average the flow compensation number and enter it. The process gives you a high- and low-flow calibration.

Another difference between the Ag Leader, Case IH AFS, Kinze Vision System and GreenStar, Ferrie points out, is that with a GreenStar, once you calibrate, the new calibration only works from that point forward.

For the best-quality yield map, keep your combine speed as even as possible, Ferrie says. "Sometimes growers calibrate their monitor, and then think they can run any speed they want,” he explains. "It's true that you calibrate so that the monitor will remain accurate as you change speeds. But even with a calibrated monitor, maintaining an even speed produces better maps.”

"Getting the best possible map may sometimes require a compromise with harvesting efficiency,” Ferrie continues. "You may want to select a harvest speed that will not force you to slow down to unload on the go. If you have downed corn, and you want to produce a good map, you may want to take the extra time to harvest all of it from the same direction, rather than from two directions at different speeds.”

If you think that sounds extreme, Ferrie has clients who stop harvesting if their yield monitor breaks down. "Getting the best possible yield map is that important to them,” he says. 

For More Information
  • Find a preharvest season maintenance checklist for Ag Leader yield monitors at Click on "Pre-Harvest Checklist.”
  • For more about how to use a good yield map, visit, and search for "Road Map to Bigger Yields.”

Take the Wheel With The Systems Approach

This story marks the beginning of our third Corn Navigator Series. Popular with readers, the series of straightforward articles helps guide corn growers in mastering the key components of The Systems Approach to high-yield corn.

You can e-mail Darrell Smith at

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