Variance and Scale Influences on Classifying and Interpreting Soil Map Units1
- W. J. Edmonds,
- J. C. Baker and
- T. W. Simpson2
Residual variance including the variance contributed by sampling and laboratory procedures, by soil profiles within circular 7-m diam sites, by sites within delineated soil bodies, and by delineated soil bodies within each of three second-order soil survey map units were evaluated using a nested sampling design. Residual variances were small for base saturation, clay, and free iron and large for pH, quartz in the sand fraction, kaolinite, and gibbsite in the clay fraction, and the oxidic ratio. Naming and interpreting map units using classes based on the dissection of variable with large residual variances will be confounded by the sampling and laboratory procedures. Distributions of variance for the soil properties studied revealed that mutually-exclusive classes were not delineated by these map units. Shortrange variability in field observable soil properties was not mapped because of the constraint of scale. Therefore, users of soil survey information would be better served by procedures for naming and interpreting map units that describe the content and pattern of occurrence of soils rather than relying on classificational units or soil series defined by limits of taxa in Soil Taxonomy to convey map unit content and interpretations.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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