1. Soil Formation and Composition
EQ: How do you scientifically describe soil? How is soil formed?
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2. EQ: How do you scientifically describe soil? How is soil formed?
Soil Formation
Soil- the loose, weathered material on Earth’s surface in which plants can grow
3 steps to soil formation
1)Begins as bedrock (solid layer of rock beneath the soil)
2)Breaks down (weathering)
3)Mixes with other materials
EQ: How do you scientifically describe soil? How is soil formed?
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3. EQ: How do you scientifically describe soil? How is soil formed?
Soil Composition
Soil – a mixture of rock particles, minerals, decayed organic material, air and water
Rock particles- sand, silt, clay
2 factors affect the rock particles and minerals found in a soil
- bedrock
- type of weathering
EQ: How do you scientifically describe soil? How is soil formed?
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4. EQ: How do you scientifically describe soil? How is soil formed?
Soil Composition
Humus
– dark colored substance that forms as plant and animal remains decay
Creates space in soil for air and water
Rich in nutrients for plants:
nitrogen, sulfur, phosphorus, and potassium
EQ: How do you scientifically describe soil? How is soil formed?
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5. EQ: How do you scientifically describe soil? How is soil formed?
Soil Color
Color of soil can vary from gray, yellow, deep red brown to black.
EQ: How do you scientifically describe soil? How is soil formed?
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6. EQ: How do you scientifically describe soil? How is soil formed?
Soil Texture
Size of particles.
Rub soil between your fingers to test.
Different names are given to soils depending on the proportion of sand, silt, and clay.
Every soil on earth is defined as sand, silt, clay.
EQ: How do you scientifically describe soil? How is soil formed?
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7. EQ: How do you scientifically describe soil? How is soil formed?
Soil Texture
Pebbles/gravel are NOT considered soil!
EQ: How do you scientifically describe soil? How is soil formed?
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8. EQ: How do you scientifically describe soil? How is soil formed?
Soil Texture is:
grainy -large-sized pieces and feels gritty, like sand.
silky -medium-sized pieces and feels powdery, like silt.
sticky -small pieces and feels gummy, like wet clay.
EQ: How do you scientifically describe soil? How is soil formed?
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9. EQ: How do you scientifically describe soil? How is soil formed?
Soil Consistency
how easily the soil clumps can be broken apart.
The soil consistency is
loose - soil breaks apart when held.
friable - soil breaks apart with a small amount of pressure from one finger.
firm - soil breaks apart with a lot of pressure between two fingers.
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10. EQ: How do you scientifically describe soil? How is soil formed?
Soil Horizons
A layer of soil that differs in color and texture from the layers above or below it
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11. EQ: How do you scientifically describe soil? How is soil formed?
Soil Horizons
Scientists classify soil into 3 horizons
A Horizon - topsoil-crumbly, dark brown soil
B Horizon – subsoil- contains clay and other particles washed down from A. Contains little humus
C Horizon – contains partly weathered rock
EQ: How do you scientifically describe soil? How is soil formed?
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12. EQ: How do you scientifically describe soil? How is soil formed?
Rate of Soil Formation
Depends on the climate and type of rock
Warm and rainy climate – soil develops quickly
Cold and dry climate – soil develops slowly
EQ: How do you scientifically describe soil? How is soil formed?
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13. Life in soil- organisms mix the soil, create spaces, make humus .
Plant “litter”, a loose layer over the soil where plants shed leaves or die
Decomposers, organisms that break down the remains of dead plants and animals live in the soil
Bacteria, fungi, earthworms, snails and beetles
Life in soil- organisms mix the soil, create spaces, make humus .
EQ: How do you scientifically describe soil? How is soil formed?
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14. Soil Types in the United States
Scientists classify soil based on:
Climate
Common plants found in the region
Soil composition
EQ: How do you scientifically describe soil? How is soil formed?
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15. Class Work and Homework
Classwork: Copy questions 1-5 on notebook paper.
Homework: Questions 1-5 using notes. See page G55.
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