Harvest gets exciting when high numbers appear on the yield monitor screen as you're going across the field. One farmer I rode with recently became very excited when the monitor readout popped over 300 bushels per acre for corn, not once, but several times. The whole field average wasn't that high, but places in the field were going that high.
How accurate are those numbers, and are those spots really yielding that much? Here are some insights based on conversations with farmers and crop consultants.
• Calibrate, calibrate! If you want to see accurate numbers, the monitor must be calibrated. This means harvesting a known amount of acreage, and weighing it by a scale son a weigh cart or over a farm or elevator scales that is known to be accurate.
• Calibrate again: If moisture or hybrid changes significantly, you need to recalibrate if you want to make sure the readings are accurate. Here's where some people draw the line and decide being close is good enough – calibrating can take time if it means harvesting off separate loads, especially if you're going to an elevator and lines are still long right now.
• 'About ' is ok? One farmer I rode with on soybeans knew his yield monitor was about 5 bushels per acre too low, based on scale tickets. Rather than bother to calibrate it, he ran with it as it was. His reasoning was that it was consistently low, so he could still get an idea of how one part of the field was yielding compared to another part of the field. The yield maps would also reflect the lower, known-to-be inaccurate yields.
• Slugs of material: If material doesn't feed into the combine evenly then the yield data may be choppy. Monitors are set to record a data point at a certain interval, like once a second. Although the map is one color once you see it, the actual data map stored somewhere inside the monitor is a series of dots representing each data point. Each dot is a certain spot within the field. If a bunch of corn or soybeans enters the machine at one time because it goes into the feederhouse as a slug, the monitor will think it's all yield from that spot.