Soil Color Contrast
This technical note provides uniform definitions for color contrast terms among the Soil Survey Manual (Soil Survey Staff, 1993), the Field Book for Describing and Sampling Soils (Schoeneberger et al., 1998), and the Field Indicators of Hydric Soils in the United States (U.S. Department of Agriculture, 1998). It also describes a new procedure to determine the difference in hue between colors.
The contact for this technical note is the National Leader for Soil Classification and Standards, National Soil Survey Center, Lincoln, NE.
In an effort to synchronize the definition among the Soil Survey Manual, the Field Book for Describing and Sampling Soils, and the Field Indicators of Hydric Soils in the United States, a provisional definition for color contrasts was field tested nationally in 1998. After the testing period, a call for final comments was requested regarding final adoption of the provisional definition. The definition and other items contained in this technical note are the result of these collaborations and deliberations.
Color contrast is the degree of visual distinction that is evident between one soil color compared with another in close proximity. In this application it is a visual impression of the prominence between a minor color component (mottle or concentration) and an associated major color component (matrix). The Soil Survey Manual provides three categories of soil color contrast:
This technical note provides guidelines to help the soil scientist assign contrast terms consistently. Determining soil color contrast is not always simple. Prominent mottles are likely the first thing one notices when observing a freshly broken piece of soil fabric. However, if a fabric has several shades and less contrast, it takes time and concentration to fully record colors and color patterns. The contrast between two colors decreases with decreasing value and/or chroma, and it becomes faint if value is 3 or less and chroma is 2 or less, regardless of differences in hue. Furthermore, there can be a considerable amount of error in distinguishing and contrasting the colors of two features, depending on the water state; the quality of light; the time of day; roughness of the soil surface; the quantity, size, and shape attributes of the two features; and boundary distinctions. Error can be exacerbated when the two features are among an intricate pattern of other soil colors. Care in the identification of soil colors in the field thus continues to be of primary importance in minimizing errors.
Definitions of soil color contrast terms
Note: If the mottle and matrix both have values of ≤ 3 and chromas of ≤ 2, the color contrast is Faint, regardless of the difference in hue.
Faint - Evident only on close examination. The contrast is faint if the:
Distinct - Readily seen but contrast only moderately with the color to which compared. The contrast is distinct if the:
Prominent - Contrasts strongly with the color to which compared. Color contrasts that are not faint or distinct are prominent.
Tabular key for contrast determination using Munsell® notation
Note: If both colors have values of ≤ 3 and chromas of ≤ 2, the color contrast is Faint (regardless of the difference in hue).
Procedure for determining the difference between hues
Munsell book of color. 1976. Macbeth, a Division of Kollmorgen Corp., Baltimore, MD.
Schoeneberger, P.J., D.A. Wysocki, E.C. Benham, and W.D. Broderson. 1998. Field book for describing and sampling soils. Version 1.1. USDA-NRCS, National Soil Survey Center, Lincoln, NE (http://soils.usda.gov/technical/fieldbook/).
Simonson, R.W. 1993. Soil color standards and terms for field use - history of their development. In Bigham, J.M., and E.J. Ciolkosz (eds.) Soil Color, pp. 1-20. Proc. Symposium sponsored by Divisions S-5 and S-9 SSSA, San Antonio, TX. 21-26 Oct. 1990. SSSA Spec. Publ. 31. ASA, CSSA, and SSSA, Madison, WI.
Soil Survey Staff. 1993. Soil survey manual. SCS. U.S. Dep. Agric. Handb. 18. U.S. Gov. Print. Office, Washington, D.C. (http://soils.usda.gov/technical/manual/).
U.S. Department of Agriculture. 1998. Field indicators of hydric soils in the United States. Hurt, G.W., P.M. Whited, and R.F. Pringle. (eds.). Version 4.0. USDA, NRCS, Ft. Worth, TX (http://soils.usda.gov/use/hydric/).