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Soil Color

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Soil Color

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  1. Soil Color GES 394 Revised by Mr. Brian Oram http://www.water-research.net

  2. Quick Review

  3. Soil Structure • What are the structural types? Answer: granular, blocky, prismatic, platy, columnar, massive, Single grain, wedge, massive • What are the grades of structure? Answer: Structureless, weak, moderate, strong • Is weak subangular blocky a full description of structure? Answer: NO – A full description would be weak medium subangular blocky(1Msbk)

  4. Soil Color • Soil color is one property that can be used to describe horizonation and soil morphology. • The change in soil color with depth is directly related to a variety of processes that are occurring in the soil, see Table 1. • The soil color does not effect the behavior of the soils, but provides insights into environmental conditions, formation processes, and other influences on the soil. • Used is used in classifying soils.

  5. Range of Soil Color • Soil Colors – soils display a wide range of soil color. • Colors can range from reds, yellow, brown, green, blue, gray and black. • Colors vary in the brightness of the color, tint, and richness. Which one of these colors is GREEN ? Greenish Gray – 10GY5/1 Dark greenish gray – 5GY4/1

  6. Describing Soil Color • Munsell Charts are used to provide standard descriptions and names of color. Munsell Chart displays 322 standard color chips. • The Munsell description is divided into three parts: • Hue • Value • Chroma

  7. Soil Hue Hue refers to the predominant wavelength of Light that is reflected by The soil. The predominant spectral color ! This chart is a 10YR - Hue

  8. Soil Color Wheel- The Range in Soil Hue In NE PA, the most commons hues are 10YR and 7.5YR

  9. Value Value refers to the lightness and darkness of a color in relation to a neutral gray scale. A Value of 0 is black. Value of 10 is absolute white (pure white). Measure of the amount of light that reaches the eye under standard lighting conditions. Gray is the midway point and has a value of 5. 0 10

  10. Soil Value

  11. Chroma Chorma refers to the intensity or brightness of the color and has also been described as the purity of the color. It has also been described as the richness of the color. A Chorma of 0 is a neutral gray and the maximum Chroma is 20, but a value of 20 is never approached, but The Chroma scale on the Munsell Chart starts at 1. 0 8

  12. Soil Chorma

  13. Describing Soil Color – Three Components 10YR 3 6 10YR3/6 – dark yellowish brown

  14. Describing Soil Color – Three Components Issue: There are 4 colors described as a dark yellowish brown.

  15. Special Cases for Describing Color • For Colors that are pure gray, white, and black. There is no chroma and no hue. The letter N (neutral) takes the place of a hue designation, such as N 2.5/ (black). • When coloring soil – use a moist soil sample. • Describe the soil color in the field. Evaluate the color with the sun at your back. No sunglasses ! • Describe a fresh face and do not crush the sample. Describe the matrix and any “mottled” patterns. • The matrix color is the dominant soil color – 50% or more of the sample.

  16. What Colors the Soil ? • Organic matter darkens the soil and is typically associated with surface layers. Organic matter will mask all other coloring agents. • Water Content – Degree of Saturation Controls the rate of nature of the biochemical reactions. Moist soils tend to be darker in color. Primary factor the oxidation state of the system. • Mineral Content Iron (Fe) is the primary coloring agent in the subsoil. The orange brown colors associated with well drained soils are the result of Fe oxide stains coating individual particles in an oxidized state. Manganese (Mn) is common in some soils resulting in a very dark black or purplish black color.

  17. Soil Coloring

  18. Black organic coatings Thank you – Dr. David Lindbo (NCSU)

  19. Red: Hematite and Goethite Yellow: Goethite Gray: No coatings Thank you – Dr. David Lindbo (NCSU)

  20. Where is the Color? • Think of the soil ped as an M&M. An M&M has a hard outer shell and then a chocolate center. • Ok – Well the uncoated soil separates (sand, silt, and clay) are gray and the minerals (Fe, Mn, Silicates, Carbonates, and Organics) create the outer shell or coating. Under Reducing Conditions Brown Soil Coating Fe203 Fe+2 in Matrix, Less Fe+3 Gray – Low Chroma SoilIron Leached from Matrix

  21. Color Patterns-Mottling • Matrix color is the dominant color in the soil. • Mottling is spots or blotches of color in the soil that differ from the matrix color. The pattern may relate to the aeration or drainage of the soil. • Gleyed colors are low chroma matrix colors with or without mottles. If the soil is gleyed it is likely to be reduced and wet for much of the year. • Mottling associated with periods of saturation and anaerobic conditions are known as redoximorphic features. • Note the soil moisture condition when describing. Soils that contain reduced iron may appear light in place, but become darker as the reduce iron begins to oxidize.

  22. Describing Soil Color- For a Redoximorphic Feature • Describe the Matrix Color – 50% or more of the soil. • Describe the color for the Zone of Reduction – This will typically be the zone with a low chroma. • Describe the color and Zone of Accumulation – This will likely be an area with a high chroma. • When describing the color, include notation to include the amount of the surface that is represented by the color. This becomes most critical in determining hydric features and in some states siting land-based wastewater disposal systems. Use the following terminology to describe abundance. < 2% - few 2-20 % - common > 20% - many

  23. Matrix Color 5YR4/4 – reddish brown Zone of Reduction 5YR7/1 (10 % -common ) Zone of Accumulation5YR5/6 (> 20% many) Note- Any Ideas of the Soil Structure????

  24. Describing Mottled Size

  25. Degree of Contrast This represents the degree of difference between the matrix and the “mottled” pattern. Types of Contrast • Faint – difficult to see in place • Distinct – easy to see in the test pit • Prominent – easy to see from outside the pit.

  26. Degree of Contrast

  27. Example Prominent 7 Distinct 6 5 Faint Value 4 3 2 1 2 3 4 5 6 7 8 Chroma Thank You Dr. Lindbo

  28. Example 2.5YR Prominent 5YR Distinct 7.5YR Faint 10YR 2.5Y 5Y 7.5Y Thank You Dr. Lindbo

  29. Examples

  30. Reduced matrix Add a,a’-dipyridyl dye – A red color – positive for reduced iron Does the soil have reduced Iron?

  31. Quick Review

  32. What is the Soil Color ? 10YR Page 8 7 6 5 4 3 10YR6/3 – pale brown 2 2 1 3 4 8 6

  33. Soil Color GES 394 Revised by Mr. Brian Oram http://www.water-research.net