Development of Students' Abilities to Match Soil Color to Munsell Color Chips

Abstract

The color of the soil along with texture and structure make up the three major soil morphological components. The matching of the soil with a Munsell color chip often seems easy for students, yet it often frustrates beginning students because of their lack of accuracy. The objective of this study was to monitor the ability of students to match the color of soil samples to Munsell color chips three times during the 10-wk quarter. Ten reference soil samples were used in a soil morphology class to measure the ability of the students to match soil colors to Munsell colors. The 10 reference soil samples used for the key had their Munsell colors calculated using the reflectance spectra of the soil. The mean score for the 1988 class did not change during the 10 wk, whereas the 1989 class significantly improved its mean score on the second try. Student scores for matching soil colors to Munsell color chips were divided into two groups based on those who scored above the 1988 mean (>19) for the first try. Students in the 19 on their first try. Students exhibited the greatest improvement in correct soil color matching from the first try to the last try with the chroma component of color; the hue and value components did not change. A dark reddish brown soil was the most difficult for the students to correctly match with the Munsell color chips, and the black soil was the easiest. S COLOR is one of the morphologic characteristics used for soil identification and classification. Shaw (1937) indicated that soil colors are distinct and definable and they can be measured and the components reported in brief and specific terms. The color Department of Soil Science, 439 Borlaug Hall, 1991 Upper Buford Circle, Univ. of Minnesota, St. Paul, MN 55108. Contribution of the Minnesota Agric. Exp. Stn. Journal no. 17373. Received 5 Sept. 1989. *Corresponding author. Published in J. Agron. Educ. 19:141-144 (1990). of the soil is the first characteristic mentioned in describing a soil, not only by pedologists but also by laypersons. Soil colors are determined in the field by visually matching the color of the sample to colored chips in standard Munsell color charts (Soil Survey Staff, 1981, p. 64). Soil colors rarely match any of the colors perfectly in the charts. The probability of a perfect match between a soil and a Munsell color chip is less than 1% (Soil Survey Staff, 1951, p. 202). The Munsell color system uses three elements of color (hue, value, and chroma) to make up a specific color chip notation. Hue is defined as the dominant spectral color or the quality that distinguishes red from orange and is related to the wavelength of the dominant component of light. Value refers to the relative darkness or lightness of the color. Chroma refers to the purity of hue or the apparent departure from neutral grays or white. Under field conditions measurements of color should be reproducible within 2.5 units of hue (one page) and one unit of value and chroma. Pomerening and Knox (1962) determined that it is not technically feasible to interpolate Munsell soil color notations more precisely than 1.0 unit for hue and 0.5 unit for value and chroma. The accuracy of visually matching soil color to the Munsell color chip in the field is determined by the incident light falling on the sample, the condition of the soil sample, the color chart surfaces, and the skill of the person making the match. Ideal light for matching soil colors would be with the sun directly overhead with minimal atmospheric interference. Soil samples are more evenly colored when rubbed so a single color is produced. For moist samples water should be added until the sample no longer darkens with additional water. Munsell color pages should be clean and unbleached by sunlight. Persons matching soil colors to Munsell colors should hold the sample so the sunlight comes over the shoulder. Soil samples can be held above the color chip or below the page where the hole J. Agron. Educ., Vol. 19, no. 2, 1990 141 in the page allows the sample to be placed near the closest matching chip. Beginning students of soil morphology find the matching of soil samples to the color chips a rather simple procedure in comparison to texturing soils by the feel method. Students, however, often become frustrated with their ability to match the soil color with the Munsell chip because they continue to make incorrect matches of soil color with Munsell colors, even after considerable practice. The objective of this study was to monitor the ability of students in a soil morphology course to match the color of soil samples to Munsell color chips.