Soil Color

Soil Color

NDWRCDP Disclaimer
This work was supported by the National Decentralized Water
Resources Capacity Development Project (NDWRCDP) with
funding provided by the U.S. Environmental Protection Agency
through a Cooperative Agreement (EPA No. CR827881-01
01-0) 0)
with Washington University in St. Louis. These materials have
not been reviewed by the U.S. Environmental Protection
Agency. These materials have been reviewed by
representatives of the NDWRCDP. The contents
of these materials do not necessarily reflect the views and
policies of the NDWRCDP, Washington University, or the U.S.
Environmental Protection Agency, nor does the mention of trade
names or commercial products constitute their endorsement or
recommendation for use.

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academic, regulatory, and private sectors of the
onsite/decentralized wastewater industry. These materials have
been peer-reviewed reviewed and represent the current state of
knowledge/science in this field. They were developed through a
series of writing and review meetings with the goal of
formulating a consensus on the materials presented. These
materials do not necessarily reflect the views and policies of
North Carolina State University, and/or the Consortium of
Institutes for Decentralized Wastewater Treatment (CIDWT).
The mention of trade names or commercial products does not
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Citation
-Lindbo, D.L., M. H. Stolt, R. Miles, and D. L.
Mokma. 2005. 3. Field Description of
Soils: Color – Power Point Presentation.
in (D.L. Lindbo and N. E. Deal eds.) Model
Decentralized Wastewater Practitioner
Curriculum. National Decentralized Water
Resources Capacity Development Project.
North Carolina State University, Raleigh,
NC.

‣ Why color?
Soil Color
• It is the most obvious and easily
determined soil characteristic. Important
characteristics can be inferred from soil
color.

Coloring agents in the soil
‣ Organic matter darkens the soil. Organic matter will
mask all other coloring agents.
‣ 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.
‣ Manganese (Mn) is common in some soils resulting in
a very dark black or purplish black color.

Color Patterns
‣ 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.
‣ Redoximorphic features are mottles that
relate to the aeration or drainage of the
soil.

Elements of soil color
‣ Coatings
‣ Structural grains

Types of Coatings
‣ Organic matter coatings
‣ Fe and/or Mn coatings (Mineralogy)

Source of Soil Colors
Material
Composition
Color
Manganese
Hematite
Goethite
Hydrated
Ferric Oxide
MnO 2
Fe 2 O 3
FeOOH
Fe(OH) 3 nH 2 O
Purplish Black
Red
Yellow
Red-Brown

Black organic coatings

Red: Hematite
and Goethite
Yellow: Goethite
Gray: No coatings

Fe-oxide coatings

Why is color important?
1 2 3

What color is this?

What color is this?

What color is this?

What are these colors?

Spectrum

PR
Hue
R
P
YR
PB
Y
B
GY
BG
G

Hue
‣ Hue is a measure of the chromatic
composition of light that reaches the eye,
such as: red (R) or yellow (Y).
‣ Hues (10R through 5Y) are divided into
four segments of equal visual steps, For
example, yellow-red (YR) hue are
identified as 2.5YR, 5YR, 7.5YR, and
10YR

Value
0 1 2 3 4 5 6 7 8 9 10

Value
‣ Value indicates the degree of lightness or
darkness of a color relative to gray;
‣ value extends from pure black (0/) to pure white
(10/);
‣ value is a measure of the amount of light that
reaches the eye, gray is perceived as about
halfway between black and white and has a
value notation of 5/.
‣ Lighter colors have values between 5/ and 10/;
darker colors are between 5/ to 0/.

Chroma
0 8

Chroma
‣ Chroma is the relative purity or strength of the
spectral color. Chroma indicates the degree of
saturation of neutral gray by the spectral color.
‣ chromas extend from /0 for neutral colors to /8
as the strongest expression of the color;
‣ Some cards have symbols such as N 6/. These
are totally achromatic (neutral color), and have
no hue and no chroma, only a value.

Hue, Value and Chroma

Munsell Color System
‣ Hue refers to the dominant wavelength of light
(red, yellow, green, etc.).
‣ Value refers to the lightness and darkness of a
color in relation to a neutral gray scale.
‣ Chroma is the relative purity or strength of the
Hue.
‣ Notation
• Hue Value/Chroma
• 10YR 5/6

10YR Page

Gley Colors
‣ Refer to colors on the Gley Pages
‣ 10Y, 5GY, 10GY, 10G, 5BG, 5B, 5B, or
5PB with value 4+ and chroma 1
‣ 5G with value 4+ and chroma 1 to 2
‣ N with value 4+
‣ 5Y with value 4+ and chroma 1
‣ Gray colors are not always Gley colors

Gley Pages

Recording Soil Colors
‣ Soil should be moist...This is the most
common way soil colors are recorded.
‣ Always use sunlight. Do not use artificial
light. Do not wear sunglasses or tinted
glasses.
‣ Always use a freshly exposed face or ped.
Do not crush or rub the soil before getting a
color.
‣ Determine the matrix and all subordinate
colors (mottles).

Size
‣ 76 mm – extremely coarse
‣ Rule of thumb
• your thumb nail is approximately 15 mm
• your pinkie finger nail is approximately 10 mm

Percent
‣ 20% - many

Each 1/4 th
of any one
square has
the same
amount of
black

Contrast
‣ Faint
‣ Distinct
‣ Prominent

Faint Contrast
‣ Evident only on close examination.
‣ Same hue (page):
• 0 to 2 units value change, and
• 1 chroma change

Distinct Contrast
‣ Readily seen but moderate to the color to
which compared.
‣ Same hue (page):
• 2 to 4 units value change and
•

Distinct Contrast (cont.)
‣ Or a hue change of 1 color chart (page):
•

Prominent Contrast
‣ Strongly contrasting colors to which they
are compared.
‣ Same hue (page):
• >4 value unit change and
• >4 chroma unit change
‣ Or a hue change of 1 color charts (page):
• >2 value unit change and
• >1 chroma unit change
‣ Or a hue change of 2 or more pages

Note that the criteria for
contrast for use of hydric
soil indicators are
different.

Example
Prominent
7
6
Distinct
Value
5
4
3
Faint
2
1
1
2
3
4 5 6
Chroma
7
8
9

7.5Y
10YR
2.5YR
5YR
7.5YR
2.5Y
5Y
Example
Prominent
Distinct
Faint

Contrast
Class
Faint
Distinct
Prominent
Code
F
D
P
Contrast
Difference in Color Between
Matrix and Mottle
Hue
same
same
same
1 page
same
1 page
2+ page
Value
0 to 2 to 0
or
and
and
and
and
or
or
or
Chroma
0

Example: Soil Ped
Matrix – 10YR 4/4
Coating – 10YR 5/6
Lining – 5YR 5/8
Depletion –10YR 4/1
Depletion –2.5Y 4/3

Example
Matrix
10YR 4/4
10YR 4/4
10YR 4/4
10YR 4/4
Feature
10YR 5/6
5YR 5/8
10YR 4/1
2.5Y 4/3
Contrast
Distinct
Prominent
Distinct
Distinct

Feature
Matrix

Matrix
Feature

Matrix
Feature

Feature 1
Feature 2
Matrix

Feature 1
Feature 2
Matrix

Feature 1
Feature 2
Matrix