Comparing bulk soil electrical conductivity determination using the DUALEM-1S and EM38-DD electromagnetic induction instruments

Earth conductivity instruments based on the principle of electromagnetic induction (EMI) are extensively used for mapping soil salinity and, increasingly, for mapping soil texture. Environmental variables such as temperature can impact sensor response beyond the effect of soil solution electrical conductivity. This study was conducted to compare the bulk soil electrical conductivity (ECa)-depth relationship between the DUALEM-1S and Geonics EM38-DD devices and to determine the effect of variable temperature environments on instrument response. The relationship of ECa to the depth below ground was investigated by raising each instrument in increments of 0.15 m up to 1.8 m above ground level. The effect of temperature on both instruments was investigated under two soil salinity levels at two sites. The instruments corresponded reasonably with theoretical models describing the ECa-depth relationships, which are primarily coil-orientation dependent. Under the effect of variable-temperature test conditions, both instruments were prone to a higher margin of error (10-40%) at lower ECa readings while the error became less significant (approximate to 5%) at higher ECa (> 100 mS m(-1)). The difference in response of the instruments can be ascribed to the temperature-dependent change in soil ECa due to a 20 degrees C diurnal temperature variation in addition to instrumental drift caused by temperature effects on the processing circuitry. The EM38-DD's real-time display and internal powering are its advantages while the lower priced DUALEM-1S does not need instrument calibration and can store data internally