YIELD VARIABILITY WITHIN A CENTRAL IOWA FIELD

Technologies to support precision farming (PF) began to emerge in 1989 when the Global Positioning System (GPS) became available to a limite d 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 inform ation 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 a ny position within a field Developing this information will require kn owing the spatial and temporal variability of plant response and will most likely be obtained by measuring yield variability. This field stu dy was designed to quantify yield variability within a 16 ha field whi ch has had consistent practices for several years. Crop yields showed a coefficient of variation ranging from near 12% in 1989 and 1992 to o ver 30% in 1990 and 1993. Rankings of the long-term relative yield for 224 locations were not stable even after 6 years when recalculated ea ch year Many PF scenarios are based on the assumption of a stable yiel d pattern within a field but only a few points in this field have exhi bited such a pattern, Perhaps stable patterns will eventually emerge, but the time frame for this to occur may be quire long. Overall, this study suggests that implementation of PF practices within the Clarion- Nicollet-Webster soil association area will reveal both difficulties a nd opportunities.