Submitted to: Geoderma
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/4/2011
Publication Date: 7/14/2011
Citation: Hadzick, Z., Guber, A.K., Pachepsky, Y.A., Hill, R., Gish, T.J. 2011. Pedotransfer functions in soil electrical resistivity estimation. Geoderma. 164:195-202. Interpretive Summary: Surface electrical resistivity tomography is a powerful method to survey and monitor soils. It is analogous to medical tomography, and allows uncovering distinctly different structural formations within the studied soil body. Because differences between soil structural units usually result in differences in soil water contents in those units, and because soil water content is very important for soil use and functioning, research has been carried out to estimate soil water content from electrical resistivity. It has been noted that relationships between soil water content and electrical resistivity are site-specific; however, no attempt has been made to show which soil properties, other than clay content, affect these relationships, and the nature and extent of the effects. We measured electrical resistivity, water content, and other basic soil properties in 120 samples from 10 depths of a sandy soil from Maryland; regression analysis was applied to find the effect of basic soil properties on the power-law dependence between electrical resistivity and water contents. It appeared that taking soil properties into account leads to the drastic improvement in accuracy of ‘resistivity – water content’ relationships. The results of this work are important to soil surveyors and crop managers in that the work indentified the feasibility and advantages of developing site-specific relationships between the electrical resistivity soil water content, and soil basic properties.
Technical Abstract: Surface electrical resistivity tomography (ERT) is recognized as a powerful non-invasive soil survey and monitoring method. Relationships between ER and soil water contents that are needed to infer the spatial distribution of soil moisture from the ERT results, are known to reflect soil properties. However, pedotransfer relationships that relate ER, water content, and basic soil properties other than clay content have not been developed. The objective of this work was to evaluate the improvement in the estimates of ER from soil water contents if soil basic properties are included in the pedotransfer equations. Soil - coarse-loamy, siliceous, mesic Typic (or Aquic) Hapludult - was sampled in 12 locations at ten depths across a 30x30-meter experimental site. The resistivity was measured in disturbed samples in four-electrode cells. Water content, bulk density, texture, organic carbon, and pH were measured in these samples. The coefficient and the exponent in the power law-dependence of ER on volumetric water content were approximated with linear regressions that included any number of measured soil basic properties as inputs. A total of 1024 regressions were compared using the Akaike information criterion, and the best model was found that provided the best approximation with minimum number of regression terms. Six soil textural classes were encountered in the samples. When no pedotransfer relationships were included, the R2 of the log-log relationships between ER and water content increased from 0.45 at 10 cm to 0.91 at 190 cm. Splitting the dataset into topsoil and subsoil subsets resulted in favorable pedotransfer relationships with R2 about 0.85 both in topsoil and subsoil. Bulk density, clay content, sand content and pH appeared to be influential soil properties. Overall, accuracy of relationships between soil electrical resistivity and volumetric water content at ten depths in highly heterogeneous sandy soil could be substantially improved if pedotransfer relationships were established.