Submitted to: Clays and Clay Minerals
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 16, 2004
Publication Date: September 3, 2004
Citation: Logsdon, S.D., Laird, D.A. 2004. Electrical conductivity spectra of smectites as influenced by saturating cation and humidity. Clays and Clay Minerals. 52:411-420.
Interpretive Summary: Electrical current can flow through soil water, especially when there are high levels of salts, and reactive clays or organic matter present. Several tools have been developed that measure how well the electrical current moves through the soil. These tools are used to map soil properties that might relate to crop yield. The soil properties that have been related to these electrical measurements include salt levels, water content, soil fertility, organic matter content, and clay content. This study showed that the electrical conductivity due to reactive clays can be very high because these clays have high electrical charges. The electrical conductivity varied according to the type of salt associated with the clay and the amount and type of electrical charges of the clay. This information will be useful for scientists who try to relate electrical conductivity to soil properties and crop yield.
The electrical conductivity in soils is often related to soil solution salinity, but contributions from charged colloids and exchangeable cations may be also important. The purpose of this study is to examine the influence of smectite properties on frequency-dependent complex electrical conductivity, EC, of hydrated clays. We used a vector network analyzer to determine the EC under alternating electrical fields for frequencies ranging from 300 kHz to 3 GHz. Four smectite clays were saturated with Ca, Mg, Na, or K and equilibrated at four relative humidities (RH) ranging from 56 to 99%. X-ray diffraction analysis was used to determine the amount of 1, 2, 3, or 4 layers of water in the interlayers. Each EC spectra was fit to an equation that included the d.c. EC, the frequency corresponding to the change in slope, and the slope of the log-log plot at the higher frequency end. Saturating cation, smectite properties, and RH significantly affected fitted components of the spectra. Low water content increased tortuosity of the flow path and reduced EC. As EC decreased, the high frequency slope increased. For each cation -- clay combination, EC was always correlated with increases in internal water content. Highly charged smectite clays and associated cations can have a large EC which should not be ignored in soil and sediment studies.