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Properties, classification, and upland oak site quality for residual soils derived from shales, phyllites, siltstones, and sandstones in southwestern Virginia
Edmonds, William J.
Rector, Dean D.
Wilson, N. O.
Arnold, T. L.
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Profiles of residual soils developed in materials weathered form shales, siltstones, phyllites, and fine-grained sandstones in Rockbridge, Botetourt, Wythe, Smyth, and Washington Counties were characterized in order (I) to select soil properties for differentiating soils developed from rocks of different time-stratagraphic units, (2) to produce a uniform correlation of these soils, (3) to evaluate the influence of soil properties on upland oak site index, ( 4) to evaluate the taxonomic classes of Lithic and Typic Dystrochrcpts as predictors of upland oak site index, and (5) to develop a multiple regression equation for predicting upland oak site index for soils classified as members of Lithic and Typic Dystrochrepts. Univariate and multivariate statistical analyses were used to evaluate differences among the parent materials, to select soil properties as differentiae, and/or to develop the regression equation for predicting site index for upland oak growing on these soils. Soils developed from rocks of the Chilhowee group contain lower amount of exchangeable bases. Therefore, we recommend that soils developed from these rocks be correlated as members of the Sylco and the proposed Sylvatus series, members of Lithic and Typic Dystrochrepts, respectively. Soils developed from rock of the Rome-Waynesboro formation contain more exchangeable K+ and sand-size feldspar. We recommend that soils developed from these rocks be correlated as members of the Litz and the proposed Chiswell series, members of Ruptic Ultic and Lithic Dystrochrepts, respectively. Soils developed from rocks of the Martinsburg and Athens and from the Brallier, Chemung, and Millboro formations that classified as members of Lithic and Typic Dystrochrepts were not separated by the properties studied. We recommend that these soils be correlated as members of the Berks and Weikert soils, a recommendation which agrees with previous correlations. Distributions of site indices were significantly different at the 10 percent level of probability for soils developed from the parent materials, with soils developed from rocks of the Martinsburg and Athens and Rome-Waynesboro formations having higher median values than soils developed from rocks of the Chilhowee group and the Brallier, Chemung, and Millboro formations. Site indices for upland oak were not significantly different at the 10 percent level of probability for soils classified as members of the loamy-skeletal, mixed, mesic families of Lithic and Typic Dystrochrepts. Site indices were slightly higher for soils classified as Lithic Dystrochrepts. These results can be explained by the well distributed rainfall pattern which decreases the importance of the greater available-water capacity of the Typic Dystrochrepts and by the higher exchangeable Cai+ and by the lower exchangeable A[J+ saturation of the cation-exchange capacity of the Lithic Dystrochrepts. A regression model based on a single value, base saturation by sum of cations (SBS), gave the highest R2 value for predicting site index for upland oak on these soils. Although no significant differences in site index were observed for classes of soils based on a limit of 20 inches to bedrock; i.e. Lithic and Typic Dystrochrepts, depth to bedrock was an important character for predicting site index on these soils. The development of a useable multiple regression equation for predicting site index of upland oak growing on these soils was influenced by collinearity of the soil and site properties, by the lack of even-aged, well-stocked timber stands at the sample sites, and by our inability to access nutrient levels and amount of available moisture during the growing season.