Evaluation of pre-taxonomy soil surveys

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Virginia Polytechnic Institute and State University


A 1954 soil survey of Bland County, Virginia, was evaluated to determine if remapping was required to meet current soil survey standards. Considerable savings of time and money may be realized if a complete remap was not required. Ten random transects were chosen to study soil landscape units which formed the basis for the evaluation of soil boundary placement. The soil landscape units were determined by evaluating slope, parent material, and landscape position for each traversed delineation. Based on a binomial distribution, a numerical rating was used to evaluate each delineation. Out of 89 total delineations, there were 70, 71, and 81 successful observations with respect to slope, parent material, and landscape position, respectively. Out of 10 random observations of slope, parent material, and landscape position, the probability of observing 7 or more correct observations was approximately 85, 88, and 99%, respectively.

Five mapping units occurring on sideslope and/or colluvial positions were sampled according to a random effects, two-level nested analysis of variance (ANOVA) design. Physical and chemical analyses of the control section for 104 profiles were determined. All soils were described in the field and classified according to Soil Taxonomy of 1975. Variability in all mapping units with respect to cation exchange capacity (CEC), base saturation, total sand, and clay content was primarily among sites within delineations. All mapping units were composed of more than one soil. Similar soils comprised major percentages of each mapping unit.

The methodology proposed by this study suggested that the Bland County soil survey could not be significantly improved upon by remapping. However, a redefinition of mapping units and redrafting onto an aerial photobase would increase its usefulness to the comparable state of many current soil surveys.