Journal of Agricultural Science and Practice

Spectral-induced polarization (SIP) of glass beads, gravel, sand and sand-clay mixtures (5, 10 and 20% clay by weight) was measured over 10 mHz to 100 Hz by employing an SR810 DSP lock-in amplifier. Phase shift (j), and real part (s¢) and imaginary part (s¢¢) of complex electrical conductivity of the materials were calculated from the measured voltage and its x- and y-components to link them to physico-chemical properties of the materials. The phase shift decreased with the increase in salt concentration in pore water and diminished above a material-specific limiting salt concentration. The imaginary part of electrical conductivity was strongly correlated with clay content of the samples. For gravel and sand, j was strongly sensitive to pore-water content at 0.1 Hz, and there was a material-specific correlation between j and pore-water content. The ratio of the real part of electrical conductivity of the unsaturated samples to that of the saturated samples increased linearly with the increasing degree of pore-water saturation (ratio of water content of a sample to its water content at saturation) except for sand+20% clay mixture, in which the real part of electrical conductivity ratio first increased linearly and then leveled off at high (» 0.6) water saturation. The real part of electrical conductivity ratio versus the degree of pore-water saturation relationship was different for sand+10% clay and sand+20% clay samples but unique for sand and sand+5% clay samples. Such relationships of real part of electrical conductivity ratio of soils to their pore-water saturation provide prospects of predicting important soil properties such as soil salinity.