Dielectric Spectroscopy Analysis of Air-Dried Soils from Plovdiv District, Bulgaria

Abstract

Measurements of the electric conductivity, σ, and relative dielectric permittivity, εr, were conducted (0.1 Hz – 15 MHz) on 40 air-dried soil probes that were subsequently analyzed for pH, iron and heavy metal concentrations and organic matter. The pH of soil probes varied between pH 5.25 and pH 7.73 (mean pH 6.70), the humus content varied between 1.07% and 2.46% (mean 1.82%). The mean content of Fe was 3.4%, which was 87 fold higher than the mean concentration of the heavy metals (Pb, Cd, Cr, Ni, Cu и Zn). We found a moderate linear relation between σ (1 MHz) and the indicated physicochemical parameters; pH (coefficient of correlation, r = 0.58), iron concentration (r = 0.44), content of humus (r = 0.37) and heavy metal concentration (r = 0.53). Similar relationships and correlation coefficients were found between εr (10 kHz) and the same physicochemical parameters. As the latter represent general biogeochemical parameters, our findings suggest that dielectric spectroscopy may provide useful approach in probing soil geochemistry and iron cycling. Furthermore, our results yield insights into the impact of various physicochemical parameters on the induced polarization of soils.