ABSTRACT
The dielectric constant of soils can also be derived based on capacitance. This method includes the soil as part of the capacitor in which the permanent dipoles of water in the dielectric medium are aligned by the electric field and become polarized. The capacitor is arranged to be part of an oscillator circuit, the resonant frequency of which allows inferring capacitance, hence soil water content (Gardner et al., 1991, Robinson et al., 1998). Capacitance probes are fast, safe and relatively cheap. Monitoring depth can reach 5 meters below the ground level, by means of appropriate installing procedures (Caruso, 2007). Response time of the probes, less than 1 second, is one of the most attractive features of capacitance probes. Influence of soil salinity and soil temperature is also reported, but literature works (Kelleners et al., 2004, Schwank et al., 2006, Schwank & Green 2007) suggest that these effects can be accounted for through adequate calibration.
