Visual Assessment and Interpolation of Low Chroma Soil Colors

Color is one of the most obvious properties of soils and is utilized in many soil evaluation strategies. Color data are usually documented using Munsell notation of hue, value, and chroma, with the latter two parameters normally documented to the nearest whole unit. Soil colors with chroma less than or equal to 2 are particularly important in soil classification and soil interpretation, especially with regard to the identification of field indicators of hydric soils. During a field study of dune soils on late Holocene barrier island landscapes, the investigators sought to improve the quality of color data by noting color value and chroma to the nearest half unit by interpolating between chips in the Munsell book. To evaluate whether interpolating color to half units of value and chroma was justifiable, a study was initiated using 23 homogenized and randomized soil samples collected from dune profiles in the study area. Moist color values were generally 6 or less and moist chromas were 3 or less, while hue mostly ranged between 10YR and 5Y. As experienced soil morphologists, we estimated moist and dry colors to the nearest half unit of value and chroma, using the same reference color book and under fixed lighting conditions. A digital colorimeter was used to measure the color of the soil samples to the nearest 0.1 unit of hue, value, and chroma. This study demonstrates that when individuals are forced to select a whole chip rather than interpolating between chips, there is a significantly greater error in the estimation of both the Munsell value and chroma. Therefore, experienced soil morphologists appear to be justified in interpolating Munsell value and chroma to the nearest half unit.