Calibrating your yield monitor: Protecting the value of harvest data

By John Fulton and Elizabeth Hawkins

For many farmers, the grain yield monitor is one of the most important precision agriculture tools on the farm. Yield maps help identify high- and low-performing areas, evaluate hybrid and variety performance, assess management practices, and guide future decisions related to fertility, drainage, seeding rates, and other inputs. In short, yield data often becomes the foundation for many precision agriculture decisions. However, the old saying still applies: “garbage in, garbage out.” If a yield monitor is not properly calibrated, the resulting maps and analyses can be misleading and may lead to costly management decisions.

Modern yield monitors estimate yield using several sensors, in particular grain flow (lb./sec), grain moisture, travel speed, and header position (turns data logging on and off). The mass-flow sensor, located near the top of the clean grain elevator, is particularly critical because it converts grain impact into an estimate of grain flow. Research has shown that calibration errors can exceed 10% when monitors are not properly adjusted, and errors increase when grain flow rates fall outside the calibration range. Multi-point calibrations that span a range of harvest flow rates consistently improve accuracy compared with simple one- or two-point calibrations.

Calibration should not be viewed as a one-time task before harvest. Grain moisture, test weight, crop conditions, and machine wear can change throughout the season. Moisture sensors should be checked periodically against an accurate moisture meter, particularly when grain moisture changes significantly during harvest. Likewise, weight calibration accuracy should be verified occasionally by comparing monitor estimates to a certified scale, grain cart scale, or weigh wagon measurements. If calibration loads begin showing errors greater than about 5%, recalibration is warranted.

Key tips for yield monitor calibration

1. Calibrate every crop each season. Corn, soybeans, and wheat flow differently through the combine and require separate calibrations.
2. Use multiple calibration loads. Four to six loads covering low, medium, and high grain flow rates provide the best accuracy.
3. Use accurate scales. Verify grain cart or weigh wagon weights against certified scales before calibrating.
4. Inspect the mass-flow sensor. Check impact plates, elevator paddles, and chain tension for wear that can affect readings.
5. Check moisture sensor accuracy routinely. Compare monitor readings with a trusted moisture meter throughout the season.
6. Calibrate across expected harvest conditions. Include loads harvested at different flow rates, moisture levels, and yield environments.
7. Recalibrate after repairs or adjustments. Changes to elevator chains, paddles, flow sensors, or major combine components affect calibration accuracy.
8. Verify calibration periodically during harvest. A quick calibration check can prevent weeks of collecting inaccurate data.

Taking a few extra hours to properly calibrate and verify your yield monitor can pay dividends for years to come. High-quality yield data delivers more reliable yield maps, stronger agronomic insights, and better-informed management decisions across the farm.

Dr. John Fulton is a Professor in the Food, Agriculture and Biological Engineering Department at Ohio State University and can be reached at fulton.20@osu.edu.

Dr. Elizabeth Hawkins is a Field Specialist in the Department of Extension at Ohio State University and can be reached at hawkins.301@osu.edu.