Question:Ken, you mentioned at the Louisville farm show last winter that a poorly calibrated yield monitor would closely match scale tickets. Why is this, and what is the best way to calibrate a monitor?
Answer:A poorly calibrated yield monitor can still match scale tickets, but it doesn’t mean it always will. And just because your yield monitor matches scale tickets for the field, doesn’t necessarily mean the monitor is calibrated correctly. A poorly calibrated monitor can under-estimate high yields just as much as it over-estimates low yields, which means you could be pretty accurate on a whole field basis. Yield monitors generate a source of geo-referenced yield data that can enable growers to document the extent of spatial yield variability within fields. That’s what we’re after—spatial variability. A well calibrated yield monitor will show more definition in our field maps, making it easier to see the management zones and the variations within those fields. We have even seen accuracy decrease slightly with a good calibration, but the maps will show better spatial variability. This can happen because now instead of over estimating by 2% and then under estimating by 2% creating a wash, we over estimate by 2% all the time. This will create a map that better shows variation and at the end of the year can be accurately scaled down 2% to show real yields. As for actually calibrating the monitor correctly, you will need to calibrate at various crop flows. Pick the most consistent yield spot in your field and run multiple loads at differing speeds. Doing so will ensure that you are calibrated for differing flows (i.e. differing yields). If your monitor will allow, run four to five different calibration loads. If your monitor will only allow for two calibration loads, like a John Deere monitor, make sure you are running both a normal flow and a low flow for increased precision and spatial variability. All calibration loads should be between 5000 lbs. and 8000 lbs. and should not be unloaded on the go. You should also avoid passing water ways or any inconsistent yielding areas in the field. Also, check the accuracy of the yield monitor calibration throughout the season by harvesting and weighing loads and recalibrating as necessary.
Consider these steps provided by Bob Nielsen at Purdue University.