SPATIAL AND TEMPORAL VARIABILITY OF SOIL MOISTURE CONTENT OBTAINED USING GPR DATA: ACCURACY, RESOLUTION, AND IMPLICATIONS FOR PRECISION VITICULTURE

The ability to optimize winegrape production necessitates an understanding of the factors that influence their spatial and temporal variability. In the U.S. and in Australia, the majority of precision viticulture has focused on investigating the link between winegrape parameters and above-ground factors, such as the training, cultivation, and harvest timing of the grapes. Through trial and error and over hundreds of years, French winemakers have learned that certain soils and meteorological conditions produce finer wines than others. However, within new-world wine producing areas, where much of the active development and experimentation of grape growing and wine making is performed, very little emphasis has been given to investigating the role of soil properties on winegrapes. This is partly due to that fact that heretofore, most soil characterization has been performed using invasive methods (such as by digging backhoe pits). These techniques are invasive and laborious, and yet still provide information at a single point in time/space only, which is often insufficient to capture the field-scale variability in soil properties that are observed in winegrapes.

We have investigated the applicability of ground penetrating radar (GPR) methods to provide very high resolution estimates of near surface water content within two California vineyard study sites: the Robert Mondavi Vineyard in Napa County and the Dehlinger Vineyard within Sonoma County. Using the travel time of ground- and reflected wave events, we estimated the dielectric constant and subsequently the soil water content of the soil layers in very high resolution at both sites. Comparison of our GPR-obtained estimates with conventional measurements of water content, soil texture and plant vigor measurements illustrated that the GPR estimates are accurate and reliable, and that water content, soil texture and plant vigor are correlated. Use of the GPR-obtained information in ecosystem numerical models suggested that high-resolution water content information is crucial for optimal management of vineyards. In this study, we illustrate the potential of GPR as a tool for investigating the spatial variability of soil water content, as well as the impact of utilizing high resolution water content information for precision viticulture practices.