The spatial and temporal organization of soil water at the field scale as described by electrical resistivity measurements

Characterizing water processes at the field scale requires an accurate and high-resolution description of the variability of representative state variables, such as water content. Obtaining these data, however, is unrealistic with conventional soil water sensors; we therefore propose an empirical approach to measure water content based on electrical resistivity. This geophysical method provides exhaustive and time-repetitive information on the resistivity of a DC signal. Resistivity can be used to estimate water content, although the interpretation is not straightforward. As the approach is inexpensive and allows for repeated high-resolution measurements, its potential benefits for the monitoring of soil water processes at the field scale warrant greater investigation. Soil electrical resistivity and soil water content were monitored at the field scale on four dates in 2006, by MuCEP (MultiContinous Electrical Profiling), which gives measurements at high spatial resolution, and by precise measurements of soil water content. The spatial organization of soil water dynamics was extrapolated from the geostatistical analysis of the spatial and temporal variability of electrical resistivity, and then improved data were obtained for the whole of the studied area. Homogeneous zones were then delineated and compared with soil units defined on a soil map. We demonstrated that the zones that had less than average soil water content over time for the whole area corresponded to those zones that had greater than average electrical resistivity values over time. The spatial similarity between these zones and the soil units defined on the soil map suggested that water flows were mainly vertical in the field. Nevertheless, our method could be used to characterize some specific hydrodynamic processes, such as lateral flows or upward capillary flows, that are usually difficult to characterize from the information derived from the soil map.