The most robust site-specific management system is based in part on high quality maps of soil data. However, creating useful, accurate maps of soil information can be complicated by the natural variability of soil characteristics. This study addresses optimal sampling locations and grid sizes for soil moisture mapping, which is a valuable input for site-specific applications that depend on moisture status, such as precision irrigation and application of chemicals which require moisture transport into the root zone. Variogram analysis of surface moisture data for a central Illinois field revealed that the geospatial characteristics of the soil moisture patterns are similar from one date to another, which may allow for a single, rather than temporally variable, variogram to describe the spatial structure. For this field, a maximum cell size of 13 meters was found to be appropriate for soil moisture. This could indicate an appropriate scale for precision farming operations or for intensive ground sampling. The temporal stability of moisture patterns was studied in order to identify optimal sampling points for field-average soil moisture. Such points were identified by calculating their deviation over time from field average. Topographic data were analyzed to determine if these sampling points could be identified from time-invariant data. While no topographic indices were identified as being strong indicators of these locations, the points tended to be located in areas that were neutral in plan curvature compared to the field average.
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