Transcript Describing Soil Color

Soil
Color
GES 394
Revised by Mr. Brian Oram
http://www.water-research.net
Quick Review
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)
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.
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 ?
Dark greenish gray – 5GY4/1
Greenish Gray – 10GY5/1
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
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
Soil Color Wheel- The Range
in Soil Hue
In NE PA, the most commons hues are 10YR and 7.5YR
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
Soil Value
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
Soil Chorma
Describing Soil Color – Three Components
10YR
3
6
10YR3/6 – dark yellowish brown
Describing Soil Color – Three Components
Issue: There are 4 colors
described as a dark yellowish
brown.
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.
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.
Soil 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 coatings
Thank you – Dr. David Lindbo (NCSU)
Red: Hematite
and Goethite
Yellow: Goethite
Gray: No coatings
Thank you – Dr. David Lindbo (NCSU)
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 Soil
Iron Leached from Matrix
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.
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
Matrix Color
5YR4/4 – reddish brown
Zone of Reduction
5YR7/1 (10 % -common )
Zone of Accumulation
5YR5/6 (> 20% many)
Note- Any Ideas of the Soil Structure????
Describing 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 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.
Degree of Contrast
Example
Prominent
7
Distinct
Value
6
5
Faint
4
3
2
1 2 3 4 5 6 7 8
Chroma
Thank You
Dr. Lindbo
Example
Thank You
Dr. Lindbo
Examples
Matrix
Feature
Contrast
10YR 4/4
10YR 6/3
Faint
10YR 6/4
10YR 4/2
Distinct
10YR 5/6
10YR 4/1
Prominent
10YR 5/4
5YR5/3
Distinct
Reduced matrix
Does the soil have reduced Iron? Add a,a’-dipyridyl dye – A red
color – positive for reduced iron
Quick Review
What is the Soil Color ? 10YR Page
8
7
6
5
4
3
2
1
2
3
4
6
8
10YR6/3 – pale brown
Soil
Color
GES 394
Revised by Mr. Brian Oram
http://www.water-research.net