Comparison of Geonics EM38 and Dualem 1S electromagnetic induction sensors for the measurement of salinity and other soil properties

Abstract

The electromagnetic induction (EMI) Geonics EM38 (G-EM38) and Dualem 1S (D-1S) sensors are used frequently for assessment of soil salinity and other soil characteristics in irrigated agriculture. We compared these two sensors to determine whether they could be used interchangeably for the measurement of apparent soil electrical conductivity (ECa) in horizontal (ECa-h) and vertical (ECa-v) coil receiver modes. Readings were taken at 201 locations identified in three irrigation districts in both modes, and statistical comparisons were made on the raw data and from maps of a 2-ha irrigated field made using 1680 horizontal mode readings. Both sensors gave the same ECa-v readings (mean G-EM38 and D-1S difference = 0), whereas the ECa-h readings were slightly greater with the Geonics EM38 than with the Dualem D-1S (mean difference = 0.075 and 0.05 dS/m for the 201 and 1680 observations, respectively). The degree of coincidence between both sensors for soil profile ECa classification was acceptable: 82% for normal profiles (i.e. ECa-h/ECa-v < 0.9) and 90% for inverted profiles (i.e. ECa-h/ECa-v > 1.1). In practical terms, Geonics EM38 and Dualem 1S sensors could be used interchangeably with similar or very close results.