Géophysique des sols et des formations superficielles : abstracts et résumés étendus

The electromagnetic conductivimeter (EM) is a tool to estimate soil salinity. It has been first used for reconnaissance surveys and is now widespreading. In our study, the EM38 (made by GEONICS) has an intercoil spacing of 1 m, allowing the measurement of soil salinity down to a depth of 2 meters. Calibration of instrument readings versus soil salinity has been done either by comparison with the four electrode probe response, or directly from the electric conductivity measurements of saturated paste extract. However, these calibrations are convenient for large surveys as long as soil porosity and soil water content are reasonnably constant, so that the calibration holds. This is not the case in irrigated lands, where soil salinity distribution may be inverted or normal, without sharp boundary between soil horizons. Furthermore, soil moisture content is highly variable and its effect cannot be neglected in surveys. In our paper we present the results of a simple calibration method which takes into account soil moisture and soil texture. Soil salinity is determinated with accuracy in the low range (1-5 dS/m) with one equation, and in the high range with another one (5-35 dS/m). These equations are applied for medium textured soils with an accuracy better than 20%. (Résumé d'auteur