Landsat-Based Soybean Field Yield Quantity & Variability Comparison to Surrounding Cropland
NIR reflectance and soybean yield prediction comparison
Above: Landsat imagery is centered on a field of interest; the different colors represent how histograms for individual fields may vary (bushels per acre are shown on axis [based on NIR reflectance]); the larger gray histogram represent soybean values in the surrounding cropland area.
Below is the histogram comparison for the actual field in the center
Assessment of field: The field in the center above is represented by the green histogram on the right that is within the larger soybean area of the cropland histogram. The field shows slightly lower yield (less than one bushel lower) than the average for the eight center bins (within the brackets), but has the same mode. The field has the same or lower variability than soybeans of the overall area (based on simply viewing the shapes of the histograms) which is a good characteristic.
A map can have continuous predicted yield values as shown below (pixels will have yield values)
Development steps for Landsat Yield Prediction Map to field extent
Yield amounts can be associated with the zones 
By mapping soybean yield with the Landsat product described here, you will have a good estimate of how much a field yielded or will yield based on NIR average reflectance; particularly if imagery is from R5 or R6. You can have an even better estimation of the differences in yield throughout a field.
Contact GIS Ag Maps if you are interested in mapping yield for other crops.