Section:
Unit: Soils
Lesson Number: PS U6 L2
Lesson Title:
Plant & Soil Science
Understanding Soil Origins
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.
Understand the soil formation process.
2.
Identify several types of parent material.
3.
Name and describe the five major factors in the formation of soils.
Time: Instruction time for this lesson: 2 - 50 minutes sessions.
Resources
Any Soils Textbook
Internet
Tools, Equipment, and Supplies

Student Notebooks

Writing tools

Student Sample of parent material factor

Predetermined grouping done

Computer access
Key Terms: The following terms are presented in this lesson and appear in bold italics:

Alluvial

Loess

Terrace
 Floodplain

Topography


Parent material
Residual soil


Topsoil
Weathering

Igneous

Leaching

Sedimentary

Subsoil
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Interest Approach
Gain interest in today’s lesson by reviewing from the previous lesson.
Who can remind the class what the five factors that influence soil development are? Call on random students around the room until you get all five (climate, topography, parent material, time, plant & animal life (organisms).
Great job on remembering what we discussed last time.
Today we are going to look at these five factors more in-depth.
Each of you is going to become an expert on one of the five factors. You are going to be dividing into groups of five and you will be responsible for teaching the rest of the group about your factor area. Please listen carefully to these instructions.
Summary of Content and Teaching Strategies
It may be more beneficial to have already predetermined the groups of five or other numbers that fit your classroom. There is a student sample on parent material included with this lesson.
However, adaptations as to how extensive you want the students to be can be made according to time frame and available resources.
I would like you to get up and move into your groups of five. Please take all of your necessary supplies with you as you will remain in these groups for the rest of today. Allow students time to reorganize.
Thank you for moving around efficiently. I am going to come around and assign each of you one of the five soil formation factors. You are then going to research that factor utilizing the textbook and Internet. You are to prepare a fact sheet that can be printed and given to each member of your group. You are responsible for the material they will be learning concerning the factor you are assigned. Please be sure to be thorough and ask questions if you don’t know what to include. Are there any questions at this point?
Move around the room and assign each student a factor. Slips could also be made ahead of time so that students can draw their factors if desired.
You will have the rest of today to research and prepare your fact sheets. You are going to have to work efficiently in order to complete this task. Tomorrow you will be expected to present your factor to your group. Once I have given you your factor, you may begin.
The rest of the instructional time should be spent roaming amongst the students to assist in guiding the direction of their fact sheets. It is also good to continually remind them how much time they have left to keep them on task. A common practice of students will be to get bogged down on appearance instead of information, so be sure to watch for this problem.
Review/Summary
Five or so minutes before the conclusion of the class, have students begin to save their work and put things up for the day. Explain to them if you expect them to be ready to teach their group at the start of the next class or if they will have time to finish tomorrow.
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Thank you for your hard work today. We will make you all soil formation experts tomorrow.
Use the choral-response e-moment to be sure students know the five factors of soil development.
As a class, let’s list the five factors of soil development. I will say the first two letters of the word and I want you all to say the factor. Work through all five factors of: climate, parent material, living organisms, topography and time.
Good job everyone.
Application
Extended classroom activity:
Utilize pictures from the Internet to spark more interest at the start or conclusion of the lesson. Give extra credit points for students to correctly bring in several kinds of rock or parent material.
FFA activity:
Discuss the parent material as students are preparing for the land classification career development event.
SAE activity:
Have a student research the various kinds of parent material found on their farm or around their home.
Evaluation
The student information sheets will act as the assessment for this activity. Be sure to have a means for them to give a copy to each member of their group and to the instructor.
Answers to Assessment:
Student information sheets will vary from student to student. Be sure they all have the basic information desired based upon the most important soil factors of the community. See the key points attached to this lesson. These points are taken from a California Soils Curriculum Lesson.
If time for the lesson is an issue, the key points could be given to the students and that could lead their research.
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Instructor Key Points for PS U6 L2
There are five major factors usually considered in the formation of soils: climate, parent rock, living organisms, topography, and time.
Parent Material
1.
Parent rock from which a soil is formed has a significant effect on its qualities.
2.
Parent materials influence the formation of soils by their rates of weathering, the nutrients that they supply, and the particle sizes that they contain.
3.
The less developed a soil is, the more influence that the parent material has on its characteristics.
4.
Mineral particle size has a great effect on the properties of soil in the field.
Climate
1.
Climate is a dominant factor in the formation of soils. Climate determines soil.
2.
The major components of climate that affect soil are precipitation and temperature.
3.
In areas of low rainfall an accumulation of lime may occur. There is insufficient water to leach the lime, so these soils are usually alkaline.
4.
In areas of high rainfall there is intense weathering and leaching resulting in acid soils.
5.
Erosion of sloping lands removes developing layers of soil and deposits them down slope.
6.
Erosion, leaching and weathering are more intense and take place over a longer period each year in warm and humid areas.
7.
Climate also has an indirect affect on soils by its action on vegetation.
8.
Changes in temperature strongly affect the rate of physical chemical weathering.
Different rates of expansion and contraction bring about cracking and peeling beginning the breakdown of parent rock. Rates of chemical reactions increase as temperature increases, if sufficient water is present.
Living Organisms
1.
The activity of living plants and animals (macro and microorganisms) has major significance on the development of soil.
2.
The kind and amount of organisms present are influenced by climate (i.e., the presence of trees will have a different effect on soil forming processes than would the presence of grasses).
3.
Microorganisms help develop soils by decomposing organic matter and forming weak
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acids that dissolve minerals faster than would pure water.
4.
Fibrous root systems of grasses have a distinctly different effect on soils than do the coarser roots of trees.
5.
Lichens, which are a combination of algae and fungi, are often the first plants that grow on weathering rocks.
Topography
1.
Topography (the lay of the land) influences drainage and runoff.
2.
Steeper hill sides typically have thinner A and B horizons than more level areas, given the same parent materials and climate.
3.
Soils on gentle slopes will have more water passing through them vertically than soils on steeper slopes.
4.
The profile on gentle slopes will be generally deeper, sustain more luxuriant vegetation, and contain more organic matter than soil profiles on steeper slopes.
5.
Soils developed in flat areas with high rainfall are often severely leached.
6.
In our hemisphere soils on west and south facing slopes receive more direct rays from the sun. They are, therefore, warmer and drier than east and north facing slopes.
7.
Soils lying in a lower land locked area receive runoff waters from the surrounding higher area. If salts are present they will be dissolved and accumulate in the "low lands" causing a salt marsh or toxic salt conditions in which no plants can grow.
Time
1.
It requires time, up to about a million years, to form soils.
2.
Rocks like granite are extremely hard to decompose.
3.
Softer rocks such as limestone take less time.
4.
As soils age they differentiate into defined profiles consisting of three different layers (A horizon, B horizon and C horizon).
5.
Horizons tend to develop faster under humid, warm, and forested conditions.
6.
A recognizable soil profile may develop in as few as 200 years or, under less favorable conditions, take several thousand years to develop.
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PS U6 L2 Student Sample
Rock

The primary starting material
Affects:
1.
important chemical factors like pH and fertility
2.
texture
Three basic kinds of rock:
1.
igneous
2.
sedimentary
3.
metamorphic
Sedimentary rock is frequently layered
Sedimentary rock makes up most parent material
Sedimentary rock underlies the developing soil in ¾ of the Earth’s land
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Sandstone, Limestone and Shale make up 99% of sedimentary rock
This rock originated as soft layers of sediment that were deposited in ancient shores, rivers and oceans
Particle size was important in determining where the sediments were deposited and what type of sedimentary rock formed
Smallest particles are carried furthest during sedimentation
Largest to smallest particles:
Sandstone

Shale

Limestone
Common limestone = Clastic variety
Clastic means broken or gragmental
Common Sedimentary
1.
Sandstone
2.
Limestone
3.
Dolomite
4.
Shale
Igneous was originally molten rock.
Size of crystals in the rock reflect the speed at which cooling occurred
Large crystals = slow cooling
Small crystals = fast cooling
About ¼ of the earth is underlain by igneous rock
Texture of soils formed from igneous rock depends on the texture of the rock
Coarse = granites
Soils derived from granite have lots of quartz – which resists weathering (tend to be sandy)
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Fine = basalts
Soils derived from basalts tend to be darker and more clayey
Common Igneious
1.
Granite
2.
Basalt
3.
Rhyolite
4.
Obsidian
5.
Gabbro
Metamorphic rocks have been modified by heat and or pressure activity upon rocks.
Metamorphosis (change) creates a more resistant material.
Marble is a more resistant rock than its starting material – limestone
Common Metamorphic
1.
Quartzite
2.
Marble
3.
Slate
4.
Gneiss
5.
Schist
Parent material can also be classified by whether they have formed soils in place (residual soils) or formed soils after being deposited elsewhere (transported soils).
Residual soils – weather in place without much disruption
Rate is slow
Soil appears to form directly on bedrock
Usually shallow
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Water-transported parent material
1. Lacustrine soils – deposited in freshwater lakes
2. Marine soils – deposited in oceans
3. Alluvial or fluvial soils are transported by running water in streams or rivers
Types of alluvial soils
1. Floodplains
2. Alluvial fans
3. Deltas
Floodplains: part of a river valley periodically inundated by flooding
Prior to the Mississippi River being contained by dikes and levees – vast stretches surrounding the river were floodplains – therefore – much of that area has alluvial – floodplain soil
Alluvial fans form below hills and mountain ranges was water flowing down these slopes carries eroded material
Deltas, such as the Mississippi or Nile Delta – deposit fine-grained material at the river mouth where river meets ocean
Gravity-transported parent material = colluvium
Colluvium slides or rolls down slopes due to the force of gravity
At the base – accumulates in material called talus
Colluvium material is subject to landslides
Wind-transported parent material = Eolian
Two types of Eolian
1.
Loess
2.
Sand
Cover sands are common in arid and subhumid areas where sandstone parent material has weathered and shifted in the wind
Sand Hills of western Nebraska is good example
Loess = silt-sized material typically blown from floodplains
Loess soils are very fertile
Loess deposits can be very deep
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