Soil Soil ColorColor

GES 394 GES 394 Revised by Mr. Brian OramRevised by Mr. Brian Oramhttp://www.water-research.nethttp://www.water-research.net

Quick ReviewQuick Review

Soil Structure Soil Structure

What are the structural types?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)

Soil ColorSoil Color Soil color is one property that can be used Soil color is one property that can be used

to describe horizonation and soil morphology.to describe horizonation and soil morphology.

The change in soil color with depth is The change in soil color with depth is directly related to a variety of processes directly related to a variety of processes that are occurring in the soil, see Table 1.that are occurring in the soil, see Table 1.

The soil color does not effect the behavior The soil color does not effect the behavior of the soils, but provides insights into of the soils, but provides insights into environmental conditions, formation environmental conditions, formation processes, and other influences on the soil.processes, and other influences on the soil.

Used is used in classifying soils.Used is used in classifying soils.

Range of Soil ColorRange of Soil Color

Soil Colors – soils display a wide range Soil Colors – soils display a wide range of soil color.of soil color.

Colors can range from reds, yellow, brown, Colors can range from reds, yellow, brown, green, blue, gray and black.green, blue, gray and black.

Colors vary in the brightness of the Colors vary in the brightness of the color, tint, and richness.color, tint, and richness.

Which one of these colors is GREEN ?Which one of these colors is GREEN ?

Dark greenish gray – 5GY4/1 Greenish Gray – 10GY5/1

Describing Soil ColorDescribing Soil Color

Munsell Charts are used to provide Munsell Charts are used to provide standard descriptions and names of standard descriptions and names of color. Munsell Chart displays 322 color. Munsell Chart displays 322 standard color chips.standard color chips.

The Munsell description is divided The Munsell description is divided into three parts:into three parts:• HueHue• ValueValue• ChromaChroma

Soil HueSoil Hue

Hue refers to theHue refers to the

predominant wavelength ofpredominant wavelength of

Light that is reflected byLight that is reflected by

The soil. The predominantThe soil. The predominant

spectral color !spectral color !

This chart is a 10YR - HueThis chart is a 10YR - Hue

Soil Color Wheel- The Range Soil Color Wheel- The Range in Soil Huein Soil Hue

In NE PA, the most commons hues are 10YR and 7.5YR

ValueValueValue refers to the lightness and darkness of a color inValue refers to the lightness and darkness of a color in

relation to a neutral gray scale. A Value of 0 is black.relation to a neutral gray scale. A Value of 0 is black.

Value of 10 is absolute white (pure white).Value of 10 is absolute white (pure white).

Measure of the amount of light that reaches the eyeMeasure of the amount of light that reaches the eye

under standard lighting conditions. Gray is the midwayunder standard lighting conditions. Gray is the midway

point and has a value of 5.point and has a value of 5.

0 10

Soil Value

ChromaChromaChorma refers to the intensity or brightness of the colorChorma refers to the intensity or brightness of the color

and has also been described as the purity 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. It has also been described as the richness of the color.

A Chorma of 0 is a neutral gray and the maximumA Chorma of 0 is a neutral gray and the maximum

Chroma is 20, but a value of 20 is never approached, butChroma is 20, but a value of 20 is never approached, but

The Chroma scale on the Munsell Chart starts at 1.The Chroma scale on the Munsell Chart starts at 1.

0 8

Soil Chorma

Describing Soil Color – Three Components

10YR3/6 – dark yellowish brown

3

6

10YR

Describing Soil Color – Three Components

Issue: There are 4 colors described as a dark yellowish brown.

Special Cases for Describing ColorSpecial Cases for Describing Color

For Colors that are pure gray, white, and black. For Colors that are pure gray, white, and black. There is no chroma and no hue. The letter N There is no chroma and no hue. The letter N (neutral) takes the place of a hue designation, (neutral) takes the place of a hue designation, such as N 2.5/ (black).such as N 2.5/ (black).

When coloring soil – use a moist soil sample.When coloring soil – use a moist soil sample.

Describe the soil color in the field. Evaluate Describe the soil color in the field. Evaluate the color with the sun at your back. No the color with the sun at your back. No sunglasses !sunglasses !

Describe a fresh face and do not crush the sample. Describe a fresh face and do not crush the sample. Describe the matrix and any “mottled” patterns.Describe the matrix and any “mottled” patterns.

The matrix color is the dominant soil color – 50% The matrix color is the dominant soil color – 50% or more of the sample.or more of the sample.

What Colors the Soil ?What Colors the Soil ? Organic matterOrganic matter darkens the soil and is typically darkens the soil and is typically

associated with surface layers. Organic matter will mask associated with surface layers. Organic matter will mask all other coloring agents.all other coloring agents.

Water Content – Degree of SaturationWater Content – Degree of Saturation Controls the rate Controls the rate of nature of the biochemical reactions. Moist soils of nature of the biochemical reactions. Moist soils tend to be darker in color. Primary factor the tend to be darker in color. Primary factor the oxidation state of the system. oxidation state of the system.

Mineral ContentMineral ContentIron (Fe)Iron (Fe) is the primary coloring agent in the subsoil. is the primary coloring agent in the subsoil. The orange brown colors associated with well drained The orange brown colors associated with well drained soils are the result of Fe oxide stains coating soils are the result of Fe oxide stains coating individual particles in an oxidized state.individual particles in an oxidized state.

Manganese (Mn)Manganese (Mn) is common in some soils resulting in a is common in some soils resulting in a very dark black or purplish black color.very dark black or purplish black color.

Soil ColoringSoil Coloring

Material Chemical Composition Color

Manganese Mn02 Purplish Black

Hematite Fe203 Red

Geothite FeOOH Yellow

Hydrated Ferric Oxide Fe(OH)3*nH20 Red Brown

Calcite CaC03 Whitish

Glauconite KMg(Fe,Al)(SiO3)6.3H2O Greenish

Black organic coatingsBlack organic coatings

Thank you – Dr. David Lindbo (NCSU)

Red: Hematite and Goethite

Yellow: Goethite

Gray: No coatingsGray: No coatings

Thank you – Dr. David Lindbo (NCSU)

Where is the Color?Where is the Color? Think of the soil ped as an M&M. An M&M has a hard outer Think of the soil ped as an M&M. An M&M has a hard outer

shell and then a chocolate center.shell and then a chocolate center.

Ok – Well the uncoated soil separates (sand, silt, and clay) Ok – Well the uncoated soil separates (sand, silt, and clay) are gray and the minerals (Fe, Mn, Silicates, Carbonates, are gray and the minerals (Fe, Mn, Silicates, Carbonates, and Organics) create the outer shell or coating.and Organics) create the outer shell or coating.

Brown Soil Coating Fe203

Under Reducing Conditions

Gray – Low Chroma SoilIron Leached from Matrix

Fe+2 in Matrix, LessFe+3

Color Patterns-MottlingColor Patterns-Mottling Matrix color is the dominant color in the soil.Matrix color is the dominant color in the soil.

Mottling is spots or blotches of color in the soil that Mottling is spots or blotches of color in the soil that differ from the matrix color. The pattern may relate to differ from the matrix color. The pattern may relate to the aeration or drainage of the soil.the aeration or drainage of the soil.

Gleyed colors are low chroma matrix colors with or Gleyed colors are low chroma matrix colors with or without mottles. If the soil is gleyed it is likely to without mottles. If the soil is gleyed it is likely to be reduced and wet for much of the year.be reduced and wet for much of the year.

Mottling associated with periods of saturation and Mottling associated with periods of saturation and anaerobic conditions are known as redoximorphic anaerobic conditions are known as redoximorphic features. features.

Note the soil moisture condition when describing. Soils Note the soil moisture condition when describing. Soils that contain reduced iron may appear light in place, but that contain reduced iron may appear light in place, but become darker as the reduce iron begins to oxidize.become darker as the reduce iron begins to oxidize.

Describing Soil Color- For a Describing Soil Color- For a Redoximorphic FeatureRedoximorphic Feature

Describe the Matrix Color – 50% or more of the soil.Describe the Matrix Color – 50% or more of the soil.

Describe the color for the Zone of Reduction – This will Describe the color for the Zone of Reduction – This will typically be the zone with a low chroma.typically be the zone with a low chroma.

Describe the color and Zone of Accumulation – This will Describe the color and Zone of Accumulation – This will likely be an area with a high chroma.likely be an area with a high chroma.

When describing the color, include notation to include When describing the color, include notation to include the amount of the surface that is represented by the the amount of the surface that is represented by the color. This becomes most critical in determining hydric color. This becomes most critical in determining hydric features and in some states siting land-based wastewater features and in some states siting land-based wastewater disposal systems. Use the following terminology to disposal systems. Use the following terminology to describe abundance.describe abundance.

< 2% - few< 2% - few2-20 % - common2-20 % - common> 20% - many> 20% - many

Matrix Color

Zone of Reduction

Zone of Accumulation5YR5/6 (> 20% many)

5YR4/4 – reddish brown

5YR7/1 (10 % -common )

Note- Any Ideas of the Soil Structure????

Describing Mottled SizeDescribing Mottled Size

Size Class Symbol Criteria

Fine 1 < 2 mm

Medium 2 2 to < 5 mm

Coarse 3 5 to < 20 mm

V. Coarse 4 20 to < 76 mm

Extremely Coarse 5 > 76 mm

Degree of ContrastDegree of Contrast

This represents the degree of difference between theThis represents the degree of difference between thematrix and the “mottled” pattern.matrix and the “mottled” pattern.

Types of ContrastTypes of Contrast

Faint – difficult to see in placeFaint – difficult to see in place Distinct – easy to see in the test pitDistinct – easy to see in the test pit Prominent – easy to see from outside the pit.Prominent – easy to see from outside the pit.

Degree of ContrastDegree of Contrast

ExampleExample

Faint

Distinct

Prominent

Chroma

Val

ue7

5

4

3

2

87654321

6

Thank You Dr. Lindbo

ExampleExample

Faint

Distinct

Prominent

10YR

2.5Y

5Y

7.5Y

2.5YR

5YR

7.5YR

Thank You Dr. Lindbo

Examples Examples

MatrixMatrix FeatureFeature ContrastContrast

10YR 4/410YR 4/4 10YR 6/310YR 6/3 FaintFaint

10YR 6/410YR 6/4 10YR 4/210YR 4/2 DistinctDistinct

10YR 5/610YR 5/6 10YR 4/110YR 4/1 ProminentProminent

10YR 5/410YR 5/4 5YR5/35YR5/3 DistinctDistinct

Reduced matrixReduced matrix

Does the soil have reduced Iron?

Add a,a’-dipyridyl dye – A redcolor – positive for reduced iron

Quick ReviewQuick Review

What is the Soil Color ? 10YR Page

2

3

4

5

6

7

8

1 2 3 4 6 8 10YR6/3 – pale brown

Soil Soil ColorColor

GES 394 GES 394 Revised by Mr. Brian OramRevised by Mr. Brian Oramhttp://www.water-research.nethttp://www.water-research.net