Remember, you only get one shot at collecting and recording yield data. Sometimes the variability in crop yield can be attributed to some historical event within the field. Look for patterns in your yield map. Patterns with straight lines tend to be artificially made. To interpret these patterns, a producer should refer to last year's management records and possibly the last ten to twenty years if they are available.
Historical records are extremely important in answering questions of yield variability.
Seek historical information from neighbors, past owners of the farm, and Court House records. Characteristics like old farmsteads and fence lines, manure, fertilizer and chemical applications, wood lots, feed lots, chemical spills, old tile lines, and compaction strips leave a long lasting effect on crop production. In addition, more recent practices such as crop variety, tillage, and previous crops should be considered. Be sure to record or map errors and variations in application of crop inputs. This may be valuable information in identifying yield variations in the map.