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									Colorado Agriscience Curriculum

Section:               Plant & Soil Science

Unit:                  Soils

Lesson Number:         PS U6 L5

Lesson Title:          Determining Soil Color

Colorado Agricultural Education Standards:
      Ag. II 10.9: The student will demonstrate an understanding of soil fertility and its effect
                   on crop production.

Colorado Science Standards:
      4.1: Students know and understand the composition of Earth, its history, and the natural
      processes that shape it.

Student Learning Objectives (Enablers)
      As a result of this lesson, the student will …

        1. Identify soil color and its causes
        2. Classify soil according to color

Time: Instruction time for this lesson: 50 minutes.

      Munsell Soil Color Charts
      Soils in our Environment

Tools, Equipment, and Supplies
        Overhead projector or computer with projector
        PowerPoint: PS U6 L5 Instructor PowerPoint
        1 copy per student of Soil Color Job Sheet
        1 copy per student of Soil Color Evaluation
        Student Notebooks
        Soil for color demonstration
        Water bottle
        Writing tools

Key Terms: The following terms are presented in this lesson and appear in bold italics:
       Hue                                                Value
       Chroma                                             Mottles

Interest Approach

Have two samples of soil at the start of class. Dampen each sample – then as the students why
the soils look different. Continue discussion until they decide they came from different parent
material and have different mineral and organic matter content.

Who can tell me what the difference between these two types of soil is? Why are they different
color? Good hypothesizing. You are correct – they come from different parent material, or may
have a different mineral or organic matter content. Today we are going to discuss soil color and
its causes. For centuries people have recognized that wearing white clothes in hot climates is
cooler then wearing dark-colored clothes because more heat is absorbed by dark colors.
Similarly, dark soils absorb more heat than do light-colored ones. Some black coal mining wastes
and dark-colored oil-shale residues reach temperatures of 150 – 158 degrees F. This temperature
would be lethal to many plants that could otherwise grow in those soils. Although black soils
having high humus content absorb more heat than light-colored soils, they also frequently hold
more water. The water requires a relatively larger amount of heat than the soil minerals to raise
its temperature; water also requires considerable heat to evaporate it. The net result is that many
dark soils are not warmer than adjacent lighter-colored soils because of the temperature-
modifying effects of the soil moisture, in fact, they may be cooler except for a centimeter or so at
the dry surface.

We are going to look at some specific soil color information. I would like for you to take notes
during today’s lesson – then at the conclusion we are going to practice determining soil color.

Summary of Content and Teaching Strategies

Objective 1: Identify soil color and its causes

Utilize PS U6 L5 PowerPoint to teach the content of this lesson. You can teach in notes format
or use the job sheet provided at the end of this lesson to guide the discussion.

Slide #2
Factors that give soil color
•Organic matter
•Weathered mineral material composing the soil
•Quantity and condition of iron present
Slide #3
Dark Color in the A Horizon
•Usually indicates the presence of organic matter
•This is a characteristic of the A horizon
Slide #4
Sub-soil Color Determination
•Quantity and condition of iron
•Red colors = usually associated with unhydrated iron oxides and indicate a well drained soil
•Yellow colors = largely due to hydrated iron oxides and generally indicate a somewhat more
moist condition than red colors

Slide #5
Basic Color Classifications
Slide #6
Color Determination in the field
•Munsell’s color charts
•Absolute black = 0
•Absolute white = 10
•Light soils hue value = 7 or more
•Medium soils hue value = 5 – 6
•Dark soils hue value = 4 or less
Slide #7
Munsell Color Charts
Hue = dominant spectral or “rainbow” color
•Red, Yellow, Blue, Green
Value = relative blackness or whiteness
•Reflected light
Chroma = purity of “color”
•Number increases and the color is more brilliant as grayness decreases
Pause here and show the class the Munsell Color Chart book

Slide #8
Change in soil color…
•Indicates a difference in the soil’s mineral origin (parent material)
•Or change in soil development
Slide #9
•Spots of different colors in the soil
•Generally indicate that the soil has periods of inadequate aeration each year
•Usually rust colored
•Bluish, grayish, & greenish subsoils (gleying) – with or w/o mottles = indicate longer periods
each year of waterlogged conditions & inadequate aeration.

We are now going to look at a variety of soils and determine the color classification. Please
gather around the lab table now.


Have a variety of soils ready that can be moistened and then compared to the Munsell Color
Charts. It is very helpful to gather a variety of soils over time when you or someone is traveling.
Ziplock bags full of a variety of soils will last a long time if you only use a small amount to
indicate color. Spreading newspaper on the table and then just putting a pinch of soil out and
wetting it down works well.

We are going to look at these soils. Discuss where they come from. As I put soil out and dampen
it, decide in your mind what color – light, medium or dark – you believe it will be. I will then call
on someone randomly to share their decision and we will look it up in the book. Are there any
questions? Continue this process with a variety of soil samples.

Extended classroom activity:
      Go out into the field and determine soil color at locations around the community.

FFA activity:
      Compete in the Land Classification Career Development Event.

SAE activity:
      Determine soil color and causes at a location around the home or business.

      Utilize the attached student evaluation as desired.

Answers to Assessment:

   1.   organic matter, parent material, iron present
   2.   presence of organic matter
   3.   light, medium, dark
   4.   Munsell Color chart
   5.   spots of different color in soil

                                                                                  Soil Color Job Sheet
Enterprise: Soils                                                         Name:
Job: Recognizing Soil Color and its causes                                Date:


   1. List the 3 factors that give soil the color you see in the field.

   2. What does dark color in the A horizon indicate?

   3. What usually determines the color of the sub-soil?

   4. What are the 3 basic color classifications?

   5. How is color determination made in the field?

                                                                             Soil Color Evaluation
                                      Soil Color Evaluation

Name: ______________________________________                    Date: _____________

   1. What factors give soil color?

   2. Darker A horizon can mean what?

   3. What are the three basic color classifications of soil?

   4. What chart is used to determine soil color?

   5. What is a mottle in the soil?


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