Failure of Pore‐Water Analyses for Dispersion

Abstract

The method of Sherard, et al., where soil saturation extract cation data are plotted on a percent sodium versus TDS (total dissolved solids in milliequivalents per liter) graph to classify clayey soils as dispersive or nondispersive, is applied to 223 soil samples from six different soil groups. The method exhibited poor overall agreement with physical test results. These data were subsequently evaluated using analysis of variance and discriminant analysis (a multivariate classification technique) which indicated that each soil group exhibits unique classification criteria based on pore‐water cation data. It appears that, for most soil groups in this study, pore‐water cation data do not provide adequate identification of dispersive and nondispersive clay soils. Reasons for the observed lack of agreement between pore‐water data and physical tests are reviewed and suggestions for further research are presented.