New Method for Characterizing Soil Contrast

Limitations of existing definitions of similar and contrasting soils for soil survey interpretations relating to both inclusions in map units and landscape patterns of soils led to the development of a new procedure for characterizing soil contrast. Six classes, or levels of soil contrast, are defined based on differences in intrinsic soil properties. Soil texture, coarse fragments, depth of rooting, drainage, permeability, pH, salinity, slope, erosion, and flooding are used to define 12 parameters for comparing soils. The range of values for each parameter is divided into a small number of discrete classes to facilitate comparisons. Within a given parameter (e.g., surface texture), class comparisons are rated as very similar, similar, somewhat contrasting, contrasting, or very contrasting, depending on whether the property values are in the same class, an adjacent class, nearby classes, or remote classes. Repeating this procedure for each parameter generates a set of 12 parameter contrasts for the two soils being compared. The distribution of contrasts among contrast levels determines the overall degree of contrast between the two soils. Where one or two parameters have a higher contrast than any of the others, that contrast level becomes the overall degree of soil contrast. Where several parameters vary at the same level, the cumulative effect of multiple variation is expressed by increasing the overall contrast to the next higher level. Advantages of the new model include multiple classes, definition of contrasts in terms of soil properties, and a precise procedure that can be duplicated by any two people given the same set of data.