Just How Good Is Yield Data?
Since its introduction, yield monitor data has gone from a novelty to a requirement for everything from variable rate planting and nutrient application to assigning values to productivity zones in fields. Many producers now have 10 to 15 years or more of yield data available for input in decision making. However, as in the case of any data, the first question that needs to be asked is how good is it?
"Early yield monitor data is as good as the operator who collected it," said Scott Shearer, professor and chair, Food, Agricultural and Biological Engineering, Ohio State University. "The way the monitor was calibrated and how the machine was run were the major factors in the quality of data."
RESOLVING TECHNICAL PROBLEMS
A 1997 side-by-side swath comparison of several makes and models of combines and yield monitors conducted by Shearer found differences in measured yield, attributable to machine and operator variability. He recalled one operator who started the wheat harvest season with wheat at 30 percent moisture and never recalibrated again as moisture levels dropped. Shearer suggested that even with the improvements that have been made in ease of calibration, calibration remains more of a concern than innate monitor accuracy. However, there were problems with early monitors.
"I think the manufacturers have done an excellent job of resolving problems such as sensor temperature drift," said Shearer. "They also recognized the importance of placement of impact and moisture sensors for improved accuracy, ease of servicing and better coordination of moisture and mass flow sensing data."
Shearer has visited and revisited yield monitor technology throughout much of his career, working his way through academic ranks to professor and later chair of the Department of Biosystems and Agricultural Engineering, University of Kentucky. Working with a grain elevator gimble in his University of Kentucky lab, he simulated a wide variety of field conditions, including grain flow rate profiles and variations in topography. Research conducted in that lab did much to encourage improvements in yield monitor accuracy.
Yet for all the improvements in the technology, one problem that can't be resolved is unrealistic operator expectations. One of those expectations arises from the name "yield monitor," when in fact, what is monitored is the impact of grain striking the sensor plate.
PHOTO COURTESY OF CLAASCalibration remains the biggest challenge to capturing accurate yield data from yield monitors. "People tend to judge the accuracy of the yield monitor by how well the accumulated mass flow rate compares to the weight of the crop across the scale," said Shearer. "In fact, the yield monitor was intended to measure the variation of yield across the field. What they need to know is how accurate the estimate of yield is for a given geographic location in the field."
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