Soil

Mr. Gilmore

Monday, October 15th • Grab a textbook! • Objective: We will explain the formation of different

soils and classify soils according to particle size.

• Review:

1. The four limestone samples illustrated below have the same composition, mass, and volume Under the same climatic conditions, which sample will weather SLOWEST? a. Sample A b. Sample B c. Sample C d. Sample D

Review

2. As particles of sediment in a stream break into several smaller pieces, the rate of weathering of the sediment will

a. decrease due to a decrease in surface area.

b. increase due to a decrease in surface area.

c. decrease due to an increase in surface area.

d. increase due to an increase in surface area.

Review

3. Which event is an example of chemical weathering?

a. rocks falling off the face of a steep cliff

b. feldspar in granite being crushed into clay sized particles

c. water freezing in cracks in a roadside outcrop

d. acid rain reacting with limestone bedrock

Review

4. What type of weathering caused the following rock feature?

Review

5. What type of chemical weathering is shown below?

2Fe + 3O2 Fe2O3

You are a Farmer

• You want to plant tomatoes

• You need to figure out what type of soil to use

• What characteristics do you look for in making your soil choice?

What is soil and where does it come from?

• Broken down rocks

• Four components:

– Minerals

– Air

– Water

– Organic

What is soil and where does it come from?

Summary

• What is soil and where does it come from?

Why are soils so different?

Why are soils so different?

• Why are you all so different?

• Factors of formation

– Parent Material (Bedrock Type)

– Climate

– Organisms

– Slope (Topography)

– Time

• Group activity

14a (left below Monday’s review)

Warm-up:

1. What are the factors affecting soil formation?

2. Which one has the greatest affect?

See me if you did not take the test or finish the test yesterday.

Why are soils so different?

• Parent Material (Bedrock Type) – Rocks/minerals/elements we are starting with

• Climate – Weathering of starting materials

• Organisms – Plants, animals, and microorganisms affect chemical

content

• Slope (Topography) – Slopes causes soils to slide or form differently

• Time – Newer soils will look different from older soils

Summary

• Why are soils so different?

How does particle size affect soil characteristics?

• Three soil sizes/textures

– Clay

– Silt

– Sand

• Other important Soil particle:

– Humus

Humus

• Decayed organic material

Particle Size

Particle Size

Soil separate particle diameter (mm)

____________________________

Sand . . . . . . . . . 2.0 - 0.05

Silt . . . . . . . . . . 0.05 - 0.002

Clay . . . . . . . . . . <0.002

SAND

SILT CLAY

How does particle size affect soil characteristics?

How does particle size affect soil characteristics?

Sand Silt Clay

Permeability (How fast does water flow through) Most Least

Penetrability (How easily can roots push through) Most Least

Nutrients Held Most Least

Page 14a (if room)

Warm-up:

1. List the different sized particles found in soil from largest to smallest.

2. What is humus?

3. How does particle size affect water retention?

How does particle size affect soil characteristics?

How does particle size affect soil characteristics?

What soil is 30% clay, 30% Silt, and 40% Sand?

What soil is 30% clay, 30% Silt, and 40% Sand?

Summary

• How does particle size affect soil characteristics?

Think-Pair-Share

• Why is there such a danger of flash floods in the Las Vegas Valley?

How does soil change as you keep digging down?

• Soil Profile: A few of a cross section of soil.

• Soil Horizon: Zones or layers in a soil profile.

How does soil change as you keep digging down?

• 4 Main Horizons

– A Horizon

– B Horizon

– C Horizon

– Bedrock

How does soil change as you keep digging down?

• A Horizon

– Top Soil

– Humus (decaying Organic material)

– Organisms (including plant roots)

How does soil change as you keep digging down?

• B Horizon

– Beneath Top Soil: Subsoil

– Contains fine clay particles

– Lowest layer for organisms

– Holds more water

How does soil change as you keep digging down?

• C Horizon

– Above Bedrock

– Partially weathered Bedrock

– Pieces of Parent Rock can be found in the C Horizon

Summary

• How does soil change as you keep digging down?

Quick Questions

1. The cross section below shows a soil profile.

This soil was formed primarily by a. Erosion by running water over a relatively long period of time. b. Weathering and biological activity over a relatively long period of time. c. Erosion by running water over a relatively short period of time. d. Weathering and biological activity over a relatively short period of time

Quick Questions

2. Which soil layer is least likely to contain humus?

Quick Questions

3. In the four following situations which two soils would be most similar?

Soil A forms from Mafic rock in a humid climate. Soil B forms from Mafic rock in a dry climate. Soil C forms from Felsic rock in a humid climate.

Soil D forms from Intermediate rock in a polar climate.

Quick Questions

4. Use the Soil-Texture triangle to answer the following question. What soil type is 30% clay, 50% sand, and 20% silt?

Quick Questions

5. A certain type of cactus needs to grow in soil that drains easily. Additionally, the roots of this cactus cannot penetrate dense soils, but does not need nutrient rich soil to grow. Of the following soils, which would be best for this cactus to grow in?

a. Silty Clay b. Clay Loam c. Sandy Loam d. Silt