YIELD VARIABILITYWITHINACENTRAL IOWA FIELD

Technologies to support precision farming (PF) began to emerge in 1989 when the Global Positioning System (GPS) became available to a limited extent and was tested as a means for locating farm equipment within fields. Substantial PF technology is available with rapidly decreasing costs and increasing capabilities. However, one major class of information that is missing is a method for determining how much material to apply or what action to take as a result of a specific condition at any position within a field. Developing this information will require knowing the spatial and temporal variability of plant response and will most likely be obtained by measuring yield variability. This field study was designed to quantify yield variability within a 16 ha field which has had consistent practices for several years. Crop yields showed a coefficient of variation ranging from near 12% in 1989 and 1992 to over 30% in 1990 and 1993. Rankings of the long-term relative yield for 224 locations were not stable even after 6 years when recalculated each year. Many PF scenarios are based on the assumption of a stable yield pattern within a field, but only a few points in this field have exhibited such a pattern. Perhaps stable patterns will eventually emerge, but the time frame for this to occur may be quite long. Overall, this study suggests that implementation of PF practices within the Clarion-Nicollet-Webster soil association area will reveal both difficulties and opportunities.