A 2D electrical resistivity tomography survey of a vineyard plot of the Gaillac appellation (France): interpretation with respect to possible implications on vine water supply

Aims: The aim of this 2D electrical resistivity tomography (ERT) survey performed on a vineyard plot of the Gaillac appellation was to investigate spatial and temporal variations in subsurface water supply in relation with pedo-geological and morphological features. Methods and results: The ERT surveys were carried out under two contrasted - dry and humid - climatic conditions. All the resistivity profiles showed the superposition of two layers: a lower layer characterized by very low resistivity values (< 40 Ω.m) corresponding to a marly molassic subsoil overlaid by an upper layer characterized by moderate to high resistivity values (300 Ω.m to 1500 Ω.m) corresponding to a silty-sandy and gravely-pebbly soil sequence. The resistivity values of the molassic subsoil stayed very low independently of water supply conditions whereas those of the soil sequence decreased by a factor 2 (300/750 Ω.m versus 750/1500 Ω.m) when the plot was close to field capacity. Conclusion: The ERT results coupled with pedological and morphological data strongly suggest that the water flow is preferentially restricted at the molassic subsoil/soil sequence interface, short-lived and of low amplitude. Significance and impact of the study: Consequently, the water supply regime, which points out a potential risk of drought stress for vine crops, implies a minimization strategy when choosing vegetal material and viticultural management operations