Changes in Field Soil Water Tracked by Electrical Resistivity

Abstract

Recently, geophysical methods have been developed that can monitor soil characteristics spatially at high resolution. However, interpreting electrical measurements is difficult because geophysical data can be influenced by many soil variables, some of which vary over time. Our objective here was to use spatial measurements of electrical resistivity to define zones of homogeneity, to interpret them in terms of changing water contents, and to compare them with a soil map. Our underlying assumption was that the time variation of electrical resistivity at the field scale was only due to the dynamics of soil moisture in our studied field. Monitoring of soil electrical resistivity and soil moisture was performed at four dates during 2006 by two methods: by the use of the MUCEP (MultiContinuous Electrical Profiling) device, which gives measurements over a whole field, and by local gravimetric measurement of soil water content. Homogeneous zones were defined directly from measurements of the electrical resistivity and after ordinary kriging of the water content. Our analysis of spatial and temporal variability has permitted us to discriminate three temporally homogeneous zones, in terms of both electrical resistivity and water content, which were broadly related to the soil map. The use of electrical measurements enabled us to directly describe spatial and temporal changes in soil water content at the field scale and to describe some hydraulic processes, like lateral flows or upward capillary flows, that would be difficult to derive from soil maps.