Bob Nielsen is a big believer in calibrating yield monitors. He's not a fan of doing it once per season or waiting until the end of the season to use software to calibrate it after the fact.
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Why not? The Purdue University Extension corn specialist says neither method usually leads to accurate results. Conditions change during harvest. Moisture of the corn changes too. If you're not recalibrating the moisture portion of the yield monitor and corn moisture content drops from say the low 20's to 15% moisture, it's likely the monitor is no longer as accurate as it was, even if it was calibrated precisely when you started the season.
It also needs to be recalibrate if you switch corn hybrids. Obviously that's impractical if you're running a test plot, and does give pause to how accurate they are. However, many people use yield monitors to run test plots.
However, Nielsen advises that if you are running whole fields and switch hybrids, you may want to recalibrate. That's especially true if the hybrid has a totally different type of kernel than the hybrid you harvested in the last field. Differences in shape and depth of kernels can influence sensor readings in the clean grain elevator, and thus influence yield results.
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In a plot last year where only two hybrids were involved, and another factor was being tested with each hybrid, it wasn't possible to recalibrate for the second hybrid, Nielsen recalls.
Error shot up on the second hybrid. Kernel size and shape was very different on this hybrid than the first hybrid which was harvested. As a result, yields for the second hybrid appeared higher than they actually were. It made accurate comparisons between the two hybrids impossible, at least with any degree of accuracy.
For good maps for yield to look at this winter, take time to calibrate now.