Albert Munsell, a professor and artist, devised a method of evaluating and classifying colors based on three properties; hue, value, and chroma, also referred to as (HVC). These properties have helped soil scientists standardize and record their observations through the Munsell Soil Color Chart, described in detail below.
Hue describes the quality we use to distinguish one color from another. Such as red, yellow, green, blue and purple. These colors form a natural order, which progresses continuously. Munsell put these colors in a circle, according to their natural progression. For instance, red will proceed to yellow, then green, and so on.
At the beginning of the colors, he inserted five boundary hues; yellow-red (YR), green-yellow (GY), blue-green (BG), etc. For colors without a hue, such as grey and black he called them neutral. Scientists can identify hues in the electromagnetic spectrum within the visible region.
The value defines the degree of lightness or darkness of a color. On the Munsell soil color chart, lightness increases from the bottom of the page to the top of the page. A scale used ranges from 0 for complete black to 10 for white. At five the value is grey.
Chroma describes the intensity, saturation or purity of a color. On the Munsell color chart, it is the horizontal axis, and scale is from 0 to 8. Grey has a weak chroma, with value 0, since it has fewer pigments or no color. Vivid colors have concentrated pigments or most color, thus a high chroma.
Munsell Soil Color Chart
The Munsell soil color chart facilitates the identification and communication of the color of soils. Wetland soils are often grey (reduced), or dark brown to black. This description, if used verbally, is not very exact; thus those undertaking the study of the soils, use the Munsell color system for consistent classification.
Munsell soil books have been the standard methods of evaluating soil for over 60 years. The USDA adopted the technique as its official system for research in the 1930s. Use of the charts significantly improved soil mapping across the country, by adding accuracy, consistency and precision.
Application of the Munsell Color System
Various other industries also use the Munsell color system. Archeologists use it when classifying soils around a site, bones, rocks, and artifacts. Forensic scientists use the system to identify soils in crime scenes.
Based on how the eyes identify color, artists employ the method when selecting colors. Photographers and image equipment manufacturers use it in balance and control of equipment. Food scientists utilized the Munsell system to create consistency in products. Other sectors include academia, health departments, landscaping, real estate, and geology.
How to Use the Munsell Soil Color Chart in a Wetland
The Munsell color chart is a collection of different pages, with color chips on them. In soil identification only two hues are used; Red and Yellow. The hue is identified by a notation on the upper right corner.
Pages in the book are prearranged to follow the natural progression, starting at most red which is the 0R and ending at most yellow 10Y. You will notice a hue notation in the series 5R, 7.5R, 10R, 2.5YR, 5YR, 7.5YR, 10 YR, 2.5Y, 5Y. The difference between hues is 2.5.
The symbol 2.5YR means two and a half parts of yellow to one-part red. Such soils are redder and found in well-drained areas. As the value of (Y) increases, the ground becomes more yellow. For wetlands with poorly drained soils, the main indicator is dark or reduced soil color. There are also a few pages in the book that are almost always represented by hydric wetland soils; the Gley pages. The word Gley is a Portmanteau (a linguistic blend of words in which parts of multiple words or their sounds are smashed into a new word), derived from Grey and Blue. These colors are often ultra-indicative of hydric soils.
Procedures when Using the Color Chart
The Munsell book has two sections. On the right page, you identify the color by matching the soil sample to the chips. The descriptive elements, hue, value, and chroma are always written following the order (HVC) for instance, 10R 3/6.
On the left page, you can determine the color name by matching this value from the right side, which has a notation. For instance, 10R 3/6 becomes dark red.
Before using the book, ensure that all the pages are readable. You can use a chip mask to hide other chips when reading the value. Also, before taking any reading, confirm that you have adequate natural lighting present on a clear sunny day and the soil should be humid but not wet. Some things to remember:
- Depending on the color of the soil in the surrounding, start at the most appropriate hue. In grey soils found in a wetland, begin on the gley page. Most people start at the 10YR page, which is the universally accepted standard.
- After determining the hue page, take a sample of soil in your right hand. Break it down to create a uniform texture and color. For dry soils, spray a small amount of water on them, but avoid soaking the soil. Excess water will make the soil sparkle in the sunlight and impair accuracy.
- Hold the soil sample behind the page you selected, and determine if it matches the selected chips. Do this, until you find the matching color chip. Next determine the value, which is the vertical reading, and the chroma, across the bottom.
Finally, note the value and match it to the left page to know the name.
When to Buy a New Book
The color chips determine the accuracy of the readings. Although Munsell Soil color books endure harsh conditions world over, they need periodic replacement. You may need to buy a new chart if:
- The book becomes outdated – the company is continuously making small alterations to values and chromas.
- To add more hues for classifying soils in new environments, such as the olive green soil chart with green-yellow color chips.
- After extended use, chips peel and fall off. They become dirty and lose their original color.
- If the book falls in a wetland or has been rained on; replace it. Avoid laminating them; it affects the way light falls on the colors making them unreadable.
Soil Properties and Colors
Back in the 1800s farmers emphasized on soil texture, and rarely on its appearance. During the early 1900s, scientists began to realize that the soil’s appearance could change. By the 1920s, Russian scientists had device three qualities to visually classify soil; tonality or shade, brightness, and saturation. Working with the Munsell Company the USDA adopted the charts in the 1930s; however, the wetland gley page was incorporated later in the 1950s. Currently, they are two gley pages used for soils in the wetlands.
Using Color to Classify Soils
The color of the soil is useful, for indicating the mineral content. It can also distinguish hydric soils (wetland) and non-hydric soils. A firm understanding of how color develops is a necessary foundation, before grasping other soil properties.
Three things influence the color of the soil; drainage, organic matter, and degree of weathering. The first process in soil development is weathering, which involves the mechanical breakdown of rocks to form soil. As they weather they release manganese and iron the two most abundant minerals in the earth surface. With time, living things die and form humus. Drainage also disrupts the color through leaching and influences the type of bacteria in the soil.
How to Interpret the Color of Soil
The color of the soil is never constant. It remains variable depending on the chemical processes taking place at any given time. Reactions include weathering, redox reactions, and decomposition of Matter by living organisms (bacteria). Climatic conditions, precipitation and geographic processes such as erosion affect the rate of these reactions.
Most aerobic soils are well-drained, and many have red, yellow, and intense brown hues. Soil with a yellow tint (10YR 8/7) has high amounts of goethite (FeOOH) crystals. Smaller amounts of goethite crystals result in brown shades. A soil with a red pigment indicates the presence of hematite (Fe2O3). These types of soils are found in temperate climates, and red hues are present in the tropics and deserts.
Anaerobic are soils that are mostly waterlogged; occurring where a table of water sets over an impermeable layer. In nature, this happens during the rainy season. When a table of water covers a layer of soil, aerobic bacteria consume all the oxygen in the water and become inactive.
Anaerobic bacteria, (thrive in low oxygen) can oxidize (Fe3+) in goethite and hematite rocks to ferrous iron (Fe2+), which is colorless. The reaction leads to the loss of the red color in hematite and goethite soils. The grey color found in hydrotropic soils can also result from the reduction of Mn4+ to Mn2+ (colorless). The reaction is responsible for soil colors in the wetland.
When a waterlogged area dries up, further reactions take place where ferrihydrite (FeOOH, dark red) is converted to lepidocrocite (FeOOH, reddish-yellow). Both have the same chemical formula as goethite, but different chemical structures.
Influence of Organic Matter on Soils
Organic matter or humus is responsible for black soils. Humus sits on the top of the soil surface, decreasing with depth. The amount of humus on the ground determines the type bacteria active and level of redox reactions.
For wetland soils, anaerobic bacteria are dominant and will thrive in soils with high organic matter. In such soils the increased humus leads to more grey soil. The property occurs in soils that are waterlogged for one season in a year.
Clear or White Soils
Indicate the presence of his amounts of calcium and magnesium. The soils are common in arid areas and form due to precipitation of carbonate in water. Carbonates may form nodules or films. They can accumulate in root pores. Such soils can also indicate prolonged washing in the area due to a humid climate.
Why are Wetlands Important?
Currently, many soil scientists are involved in the identification of hydric soils, which indicate the presence of a wetland. Before the 19th Century, during the colonial times, wetlands covered an estimated 200 million acres of land in the US. The government encouraged people to convert and use them for agriculture. Floodplains and wetlands, reduced in acreage, in turn leading to more agriculture production.
The conversion of the wetlands created a host of problems, which were not anticipated. The first negative consequence was the destruction of hydrophytic vegetation and disruption of the wetland hydrology. Some implications of fewer wetlands are still experienced today, such as flooding due to the short residence time of surface runoff water on land.
Wetlands used to slow the movement of water, reducing soil erosion, and recharged underground stream. They further provided storage of flood waters and filtered toxins.
At the end of the 20th century when most wetlands, had become agriculture farmland; the benefits of wetlands emerged forcing the government to implement laws to restrict their use. Laws against the exploitation of wetlands have since become strict. Landowners under the Wetlands Reserve Program (WRP) receive compensation for restoring wetlands in their properties.
Soil scientists are important for the ongoing identification of wetlands. The legal wetland delineation process involves identifying hydric soils, wetland hydrology and hydrophytic vegetation in any area. To identify and record these three parameters, scientists use soil pits dug to at least 16” depth, aerial coverage of vegetation estimates, and real-time observations of hydrology (even if past events).
Purchasing the Munsell Soil Color Chart
Products from Munsell are accessible from their main website or Amazon. The full book runs around $195. A more reasonably priced, smaller, and more waterproof option does exist! The Globe Soil Color Book is an alternative for the color chips, based on the same system. In the Globe Soil Book, hues appear as stripes employing the same pattern used in the Munsell soil book.
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Read More At:
- Percent Agriculture on Hydric Soil, EnviroAtlas National Data
- Soil Surveys
- NYSWF Wetland Soils
- Munsell Color Products
- The Color of Soil | NRCS Soils
- Munsell Hue Circle Poster | Munsell Color System; Color Matching from Munsell Color Company