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Enlightening Research

Special instrumentation for soil SP method is needed

solid state Ag-AgCl electrodesLandMapper ERM-02, in addition to electrical conductivity and resistivity measurements also allows non-invasively measure natural electrical potentials in soils and plants when two special non-polarizing electrodes are connected to MN terminals (Figure 3).

Potentials generated by subsurface environmental sources are lower than those induced by mineral and geothermal anomalies and often associated with high noise polarization level (Corwin, 1990). Therefore, the usage of non-polarizing electrodes is mandatory when the SP method is applied in soil and environmental studies.  The non-polarizing electrode consists of a metal element immersed in a solution of salt of the same metal with a porous membrane between the solution and the soil (Corwin, 1990).  Because of easy breakage of the membrane and leakage of the electrode solution we adopted firm non-polarizing electrodes (carbon cores from the exhausted electrical cells) to develop non-polarizing electrodes for soil studies (Pozdnyakov, 2001). In addition, low-polarizable and non-polarizable electrodes used in medical studies (available from Landviser, LLC or directly from In-Vivo Metrics, CA) were successfully used on soils/plants in the field and lab conditions. For soils with high potential differences between horizons gold-plated electrodes can be used. For seasonal monitoring in plant physiology we recommend high quality solid sintered Ag-AgCl sensor electrodes (Figure 7). Those silver-silver chloride electrodes are very stable and performance is exceptionally reproducible. Should the electrode surface become damaged or contaminated, a new surface can be exposed with sandpaper to restore the electrode's original performance.

To measure small electrical potential differences in soils accurately, in addition to non-polarizing electrodes, the measuring device should be modified and as such should have isolated connectors and high internal impedance. Most leading geophysical resistivity instruments, such as ABEM SAS, Syskal, and Sting provide such connections, but coupling electrodes are bulky, leaky and generally not useable in plant/soil studies. LandMapper ERM-02 with self-potential measuring capability and easy coupling with medical-grade non-polarizing electrodes.  

Detail description of SP method with LandMapper ERM-02 and case studies were presented in (Golovko and Pozdnyakov, 2010). The technique was tested in a few case studies, summary of which is provided below.