Statistical verification of soil discontinuities in Virginia.

Soil discontinuities, defined by significant texture and mineralogical, and/or age differences, are usually verified from a small number of pedons without producing information about the local distribution of properties that define the discontinuity. A discontinuity has geomorphic significance as well as important implications for interpretations. Along the western footslopes of the Virginia Blue Ridge, Typic Paleudults and Typic Fragiudults seem to have two depositional sequences in the sole: soil texture differences and abrupt color changes are present. Our objective was to show the discontinuity occurring in the soils using data analysis and multivariate statistics. Stratified systematic unaligned sampling within a 50-m(2) area, the Wilcoxon Signed-Rank test, principal component analysis, and discriminant analysis were used to verify the discontinuities at four locations. Twenty-five soil properties were evaluated by the Wilcoxon Signed-Rank test. Nineteen significantly different properties (P = 0.10) were detected at Site 1, 17 at Site 2, 13 at Site 3, and 15 at Site 1. The first principal component (PC) loadings showed most properties contributed about equally to the first PC, with the exception of clay-free properties at Site 2 and Site 4. The second component loadings also identified clay-free properties as the best indices for defining the discontinuities. Discriminant analysis of scores from the first five principal components showed the components contributed from 91 to 96% to the discriminant functions. Discriminant functions clearly separated Unit A from Unit B at each site. Hotelling's T-2 test showed the distances were significant (P less than or equal to 0.001) between Unit A and Unit B multivariate means. We conclude discontinuities are present at the four locations, and they can be differentiated spatially by textural differences and clay-free indices.