Fifty Shades of Gley-Using Munsell Soil Color to Assess Pine Bark’s True Colors

Aged pine bark is a commonly used organic substrate component in the southeast United States. Growers often select bark they want to use by its color, smell, "feel," and consistency in addition to physical and chemical properties. Color has been suggested as a sensory property to evaluate the aging process of composts and other organic materials, but its use as a characterizing parameter to assess the quality of pine bark substrates has not been investigated. The Munsell Soil Color system is frequently used to quantify and analyze the color of different soils. It consists of approximately 250 colored chips arranged on hue cards. Three coordinates - hue, value, and chroma - are used to describe the colors. Hue refers to the dominant spectral color, with red (R), yellow (Y), yellow-red (YR) green-yellow (GY), gray (GLEY), and white being the dominant hues in communicating soil color. The Munsell soil hue cards include 10R, 10YR, 2.5Y, 2.5YR, 5Y, 5YR, 7.5YR, 10Y – 5GY, GLEY 1 and 2, 5R, 7.5R, and white. Value indicates the degree of lightness or darkness of a color on a gray scale ranging from black to white. In the Munsell color charts, value ranges from 0 (pure black) to 10 (pure white). Chroma is the purity or saturation of a color. Chroma ranges from 0 (neutral colors) to 8 (strongest color) in the Munsell color system. A long term study was implemented to quantify the effects of aging and pile management of pine bark substrates. Fresh pine bark was processed and the ½” fines were placed in three replicated piles with 250 cubic yards of material per pile. As part of a larger project looking at the physical, chemical, and biological properties of pine bark during the aging process, the use of the Munsell Soil Color book is being utilized as a tool to assess color changes. Over the course of seven sampling dates we observed that the color of the bark darkened with age. This is expressed in the decreasing value/chroma coordinates of the Munsell hue cards (read as hue, value/chroma), which were 5YR, 3/4; 2.5YR, 3/4; 5YR, 2.5/2; 2.5YR 2.5/2; 5YR, 2.5/1; 2.5YR, 2.5/1; and 2.5YR, 2.5/1 on day 0, 52, 84, 112, 146, 173, 211 respectively. The Munsell Soil Color system shows potential as a tool to help better quantify the use of color as a parameter to assess the pine bark aging process.