Just How Good Is Yield Data?
This leads to the problem of assumed position for mapping purposes. Although yield monitors gather constant data points for the grain mass flow rate striking the sensor, they don't necessarily reflect the actual mass per unit area produced at corresponding GPS coordinates.
"There is an averaging effect that takes place as the grain moves from the header through the combine threshing and cleaning mechanisms, in particular when the cylinder is full, and finally to the clean grain elevator," said Shearer. "As combines continue to get bigger, there is more averaging over greater areas."
The time delay from where the grain was harvested and where the mass flow data point was collected when the combine is at full field speed can be misleading. The impact of this delay is multiplied with adjacent passes in a field when pass-to-pass yield comparisons are made. This difference can be amplified when making adjacent harvest passes in opposite direction on sloping fields. Shearer emphasized the importance of making adjacent passes in the same direction with all operating parameters as similar as possible when using yield monitors to compare test plot results or treatment difference.
Any correction of these problems is going to come with a cost, suggested the researcher. "Looking ahead, reflectance-based biomass sensors mounted on the header may have some potential for improving accuracy and resolution," said Shearer. "We may even see hybrid systems where mass flow sensors are augmented with relative reflectance sensors."
Since the first yield monitors were introduced, they and their data have come a long way. Where sensor technology and yield monitor accuracy go in the future is an economic decision, suggested Shearer. One thing is certain, the more accurate the yield estimates, the more real value these data will carry.