Field Comparison of Electrical Resistance, Electromagnetic Induction, and Frequency Domain Reflectometry for Soil Salinity Appraisal

Abstract

By using different physical foundations and technologies, many probes have been developed for on-site soil salinity appraisal in the last forty years. In order to better understand their respective technical and practical advantages and constraints, comparisons among probes are needed. In this study, three different probes, based on electrical resistance (ER), electromagnetic induction (EMI), and frequency domain reflectometry (FDR), were compared during a field survey carried out in a large salt-threatened agricultural area. Information about the soil bulk electrical conductivity (σb) at different depths was obtained with each of the probes and, additionally, other soil properties were also measured depending on the specifications of each instrument and, moreover, determined in samples. On average, the EMI and FDR techniques could be regarded as equivalent for σb measurement, whereas ER gave higher σb values. Whatever the case, EMI, and also ER, had to be supplemented with information about soil clay, organic matter, and water mass fractions to attain, despite this effort, poor soil salinity estimations by means of multiple linear regression models (R2 < 0.5). On the contrary, FDR needed only probe data to achieve R2 of 0.7, though root mean standard error (RMSE) was still 1.5 dS m−1. The extra measurements and calculations that modern electrical conductivity contact probes integrate, specifically, those based on FDR, remarkably increase their ability for soil salinity appraisal, although there is still room for improvement.

Review of Crop Response to Soil Salinity Stress: Possible Approaches from Leaching to Nano-Management

“…The spacing between electrodes influences the depth to which data are collected, and multiple electrodes on one instrument can collect data at multiple depth intervals. Electrical resistivity is the oldest and probably most widely used proximal sensing technique to determine soil salinity [107].…”

Assessment and Mapping of Soil Salinity Using the EM38 and EM38MK2 Sensors: A Focus on the Modeling Approaches

“…This is mainly amplified by the measurements of apparent electrical conductivity (ECa), which have been found to be correlated with soil salinity estimates and can be used as an indirect indicator for many soil properties [20]. Frequency domain reflectometry (FDR) technology, including WET sensors, has also been successful in the appraisal of soil salinity in the laboratory [21][22][23] and in situ [19,24] using ECa measurements. Nevertheless, the single utilization of these probes might be exacting and locally restricted since they have a substantially smaller measurement volume and are invasive, as their operation is based on contact with the soil and its sublayers [24].…”

“…Frequency domain reflectometry (FDR) technology, including WET sensors, has also been successful in the appraisal of soil salinity in the laboratory [21][22][23] and in situ [19,24] using ECa measurements. Nevertheless, the single utilization of these probes might be exacting and locally restricted since they have a substantially smaller measurement volume and are invasive, as their operation is based on contact with the soil and its sublayers [24].…”

Depth-Specific Soil Electrical Conductivity and NDVI Elucidate Salinity Effects on Crop Development in Reclaimed Marsh Soils

“…In addition, the measurements cannot be repeated at the same locations since the soil sampling procedure is destructive. Alternatively, networks of permanently installed electromagnetic sensors can be used to measure the soil moisture, temperature and bulk electrical conductivity at fixed depths [4]. Although such an approach yields quasi-continuous measurements in time, it provides only limited spatial information at the locations where the sensors are installed.…”