Relationship between soil electrical conductivity and water content: A multiscale petrophysical calibration

Electrical resistivity tomography (ERT) is widely used to study water transfer dynamics in soils, but accurate quantification depends on petrophysical relationships that must be calibrated. Traditionally, calibration is done either in the laboratory on undisturbed samples or directly in the field. This innovative study addresses a crucial scientific question by exploring how spatial scale influences petrophysical relationships and its implications for water content estimation. This study uses a novel experimental setup that compares three distinct footprints within a heterogeneous soil profile: (1) laboratory calibration on centimetric samples, (2) field calibration using decimetric quadrupole (QDR) arrays, and (3) decametric ERT profiles. The results reveal consistent value ranges across scales. The main results show that it is preferable to choose laboratory calibration method to prevent generating additional systematic errors that can be created by ERT and QDR approaches. Moreover, it is preferable to use a calibration based on multiple samples to better capture soil heterogeneity at decametric scales. These findings provide insights into how petrophysical relationships should be considered in heterogeneous natural soils and highlight the uncertainties of corresponding water content estimates.