Determination of Soil Pore Water Salinity Using an FDR Sensor Working at Various Frequencies up to 500 MHz

Abstract

This paper presents the application of a frequency-domain reflectometry (FDR) sensor designed for soil salinity assessment of sandy mineral soils in a wide range of soil moisture and bulk electrical conductivity, through the determination of soil complex dielectric permittivity spectra in the frequency range 10–500 MHz. The real part of dielectric permittivity was assessed from the 380–440 MHz, while the bulk electrical conductivity was calculated from the 165–325 MHz range. The FDR technique allows determination of bulk electrical conductivity from the imaginary part of the complex dielectric permittivity, without disregarding the dielectric losses. The soil salinity status was determined using the salinity index, defined as a partial derivative of the soil bulk electrical conductivity with respect to the real part of the soil complex dielectric permittivity. The salinity index method enables determining the soil water electrical conductivity value. For the five sandy mineral soils that have been tested, the relationship between bulk electrical conductivity and the real part of dielectric permittivity is essentially linear. As a result, the salinity index method applied for FDR measurements may be adapted to field use after examination of loam and clayey soils.

Simultaneous Monitoring of Soil Water Content and Salinity with a Low-Cost Capacitance-Resistance Probe

“…Moreover, the metrics of fitting regression would have shown a slope and intercept of 0.837 and 0.680, yielding very similar results to those obtained by Malicki and Walczak in their work. With some limitations, the model by Malicki and Walczak might therefore be used in capacitance applications as well as TDR [21] and frequency-domain reflectometry [10]. …”

“…The value of θ is related to ε’ only. On the other hand, ε″ changes according to soil salinity, soil temperature ( T ), and the operating frequency of the sensor [5–10]. Especially in low-cost sensors working at low frequencies (<1 GHz), the contribution of ε″ in saline soils cannot be ignored [3,11,12].…”

A TDR-Based Soil Moisture Monitoring System with Simultaneous Measurement of Soil Temperature and Electrical Conductivity

“…Simultaneous measurement of soil electrical conductivity and bulk dielectric permittivity in the same soil volume can be used to determine soil salinity, i.e. , electrical conductivity of soil water extract [31,59]. Also, temperature dependent soil electrical conductivity can be corrected to the normalized value at 20 °C or 25 °C because both variables are recorded by the monitoring system.…”

Spatiotemporal Distribution of Soil Moisture and Salinity in the Taklimakan Desert Highway Shelterbelt

“…Information about the spatial patterns of soil moisture content and salinity on the field scale are lacking in this region. Soil salinity and moisture are highly variable over time and space [19][20][21][22], especially in harsh environments. To understand the factors governing hydrological process, information is needed about the spatiotemporal evolution of soil moisture and salinity under saline drip irrigation.…”