Ten extra minutes at harvest is all it takes to adequately calibrate a yield monitor, says Paul Jasa, University of Nebraska Extension engineer. Unfortunately, some farmers fail to invest their time in that endeavor and end up reaping bad data that could misguide their management decisions for years to come.

“Almost every farmer knows they're supposed to calibrate their yield monitor before harvest,” says Jasa, “but I don't think enough of them take the time to do it, or do it properly.”

Crop consultants, grain elevators and seed dealers will sometimes calibrate yield monitors for their clients, but most farmers should be tech-savvy enough to take care of it themselves, says Jasa. “The only hassle is lining up a weigh wagon to measure the loads,” he adds.

Proper calibration requires using a scale to weigh grain and a standard moisture tester to determine grain moisture content, says Jasa. The numbers attained from these measurements can then be entered into the yield monitor's computer so that the system's sensors are set to display and record the correct moisture content and grain flow rates while operating in the field.

The calibration procedure for most yield monitors typically involves harvesting several loads at different grain flow rates, says Jasa. The first load is harvested under normal operating conditions. The next several loads are taken at reduced grain flow rates, such as ¾ speed (or ¾ cut width), ½ speed (or ½ cut width), and ¼ speed (or ¼ cut width).

“If varying the speed, keep the width of cut constant; or likewise, if varying width of cut, keep the speed constant,” says Jasa. “This calibrates the mass flow sensor for the high- and low-flow rates that occur when harvesting high and low areas in the field.”

The goal is to calibrate the equipment for variable grain flow rates — not variable loads, he emphasizes. “The main error is that farmers calibrate several different-sized loads at full speed ahead rather than calibrating for reduced speeds or reduced grain flow,” he says.

Farmers can use the hydrostatic drive on the combine to vary the ground speed and keep the grain flow rate fairly constant for each load. “Most yield monitors can show grain flow rate through the combine in bushels per hour,” Jasa points out. “Research and experience have shown an improved calibration can be obtained by using this reading on the display to operate the combine during calibration. For instance, if the grain-flow rate under normal operating conditions is 1,800 bu./hour, then calibration loads should be run at 600, 900, 1,200, 1,500, 1,800 and 2,100 bu./hour.”

The idea is to calibrate both above and below normal grain flow rates, says Jasa. Otherwise, the yield monitor will tend to overestimate the low grain-flow rates and underestimate the high grain-flow rates, he adds.

If done right, farmers typically only need to calibrate once per season per crop, says Jasa. The exceptions to this rule are when hybrids differ drastically in maturity (early vs. late), moisture content (high vs. low) or purpose (food grade vs. feed corn) or after yield monitor components have been cleaned or replaced.

“Some farmers think that if it was calibrated last year, it's good enough for this year,” says Jasa, “but that's not always true.”

For instance, if the grain elevator chain or the grain-flow sensor has been taken out, replaced or cleaned, yield monitor readings will likely be drastically different than before, he says. Also, a switch from harvesting corn above 21-22% moisture to lower moisture levels, or visa versa, will also likely require separate re-calibrations.

Jasa advises farmers to review the owner's manual before harvest begins. “Take the time and plan how to do it right,” he says. “If the yield monitor is calibrated wrong, it will give you wrong answers to questions you might have about the crop's performance.”