Use of Physical Methods to Expand Soil Survey Interpretations of Soil Drainage Conditions

Abstract

AbstractClassification systems of soil drainage conditions are used in the soil survey program to characterize hydrodynamics of soils in the field and these data are used for soil survey interpretations. Estimates of soil permeability and internal soil drainage, based mainly on inferences made from morphological features, and an estimate of runoff are used in the Soil Survey Manual to determine the placement of a soil in one of seven drainage classes. Different soil moisture regimes are defined in the new soil taxonomic system in terms of measurements made in situ. These methods do not provide the quantitative data needed for predicting what soil behavior will be under environmental conditions that have changed temporarily or permanently. Complex numerical procedures and simple approximate physical methods, both requiring hydraulic conductivity and moisture retention data, can be used to calculate hydrodynamic soil behavior for a variety of simplified boundary conditions. Two approximate methods were applied to four Wisconsin soils in which measurements of hydraulic conductivity had been made in situ. This work revealed that two soils that had been placed previously in different drainage classes on the basis of differences in soil mottling, actually had comparable hydrologic properties.