Title: Soil spatial heterogeneity effect on soil electrical resistivity Authors
|Hill, Robert -|
Submitted to: BARC Poster Day
Publication Type: Abstract Only
Publication Acceptance Date: March 16, 2009
Publication Date: April 15, 2009
Citation: Hadzick, Z.Z., Guber, A.K., Hill, R.L., Rowland, R.A., Garzio-Hadzick, A.M., Pachepsky, Y.A. 2009. Soil spatial heterogeneity effect on soil electrical resistivity. BARC Poster Day April 15, 2009.. Technical Abstract: Electrical resistivity (ER) is growing in popularity due to its ease of use and because of its non-invasive techniques, which are used to reveal and map soil heterogeneity. The objective of this work was to evaluate how differing soil properties affect the electric resistivity and to observe these effects spatially in a coarse-textured soil. The 20x20-m study plot was located at the USDA-ARS OPE3 agricultural field located in Beltsville, Maryland. Relationships between ER, bulk density, and soil water contents were first studied in disturbed 80-cm3 soil samples. The samples were collected from 10 depths in 20 cm increments. Soil water contents were brought to six predetermined levels in each sample and were in the range from air dry to 0.27g g-1. The soil samples had varying bulk densities that ranged from 1.28 g cm-3 to 1.45g cm-3. The ER in soil samples decreased as the gravimetric water content increased. The ER decrease became more pronounced as bulk density decreased. Additional soil samples were taken at field water contents from 10 depths at 12 locations. Particle size distribution, pH, water content, and ER were measured in each sample. Bulk density values found below 80 cm in the soil profile ranged from 1.5 to 1.8 g cm-3. A dependence between ER and water content could not be established in this soil layer where the lowest values of ER was recorded. The low ER values below 80cm in the soil profile could be due to lower pH values not found in the upper soil horizons. The lowest sand contents corresponded to highest ER values in this soil layer. Lastly, vertical electrical sounding (LandMapper ERM-02) was used to infer spatial distribution of soil resistivity along a 9-m transect at OPE3 agricultural field. This was done on different dates when the soil was dry and when it was wetted with low-intensity rains. The Wenner-Shlumberger array with 31-electrodes spaced 30-cm apart was used. Soil temperature and water content were monitored at 10 depths down to one meter during ER measurements using a multisensor capacitance probes (SENTEC). Averaging ER data along the transect resulted in a good correspondence with data from soil samples as described above. The gradual increase in ER values from the surface to the depth of about one meter probably reflected the general increase in bulk density and changes in soil texture. The small ER values found at the lowest depths with sounding were similar to those observed in samples from large depths. Depending on the range of their values, both bulk density and soil texture apparently affected or did not affect the ER. Coupling the information on soil properties in the soil profile with the sounding data appears to be useful for interpretation of general trends in sounding results.