Abstract
Pedological soil surveys usually based on auger sampling encounter methodological and economic difficulties. Electrical resistivity (ER) techniques could be used as a simple and practical method to determine their spatial variability. However, attempts to map soils using ER techniques have very often limited success, especially in bottomland areas, due to large variations inherent in ground data. The aim of this study is to seek the interest of a geophysical method, the radio magnetotelluric-resistivity (Radio-MT), to map field-scale hydromorphic horizons for loamy pedological systems in bottomlands characterized by large variations of soil water content and depth to upper boundary of saprolite. The sampling survey was carried in the Armorican massif (western France). The electrical measurements were taken along transects on an agricultural field (80×150 m). The soil sampling was performed on a regular grid with a mesh of 10 m. On each point, some soil properties were measured (type and thickness of the loamy horizons, depth to the upper boundary of saprolite, soil water content at 10, 20, 40 and 60 cm depths). A direct relationship between apparent resistivity and horizon type distribution was not established. The best correlations were between the electrical conductivity and depth to the upper boundary of saprolite and topsoil water content. The correlation coefficients, r, are 0.51 and 0.34, respectively. To identify the soil types, we modeled the influence of these two soil properties by multiple regression technique. Deviations from the regression model were then interpreted by taking into account the succession of soil horizons. These results seem to indicate that the electrical method used in this study could not be directly used to evaluate spatial prediction of the hydromorphic soil distribution, but indirectly by taking into account soil properties such as the soil water content and the upper boundary of saprolite.
Published Version
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