1. Soil Composition – What Dirt is Made of
Rock particles
Minerals
Dead, decaying plant and animal material (humus)
Bacteria, fungi and other microbes
Worms and insects
Air
Water

2. 1. Why is Dirt Important?
Soil contains the minerals and nutrients that plants need to grow.
Soil provides shelter for plants and animals.
Soil absorbs, stores, and filters water.

3. Profile = Layer of soil also called horizon.
Litter (hummus) – dead leaves, grass, and waste material
A. Topsoil – rock pieces, nutrients, water, air and decaying matter (most animals live here)
B. Subsoil – rock fragments, water and air. (less plant/animal matter)
D. Bedrock – rock that makes up Earth’s crust.

4. Relative Size Comparison of Soil Particles
     There is disagreement in the scientific community about the exact size ranges of sand and silt. For GLOBE, we will measure sand and silt based on two different size definitions.
Barrel
                                     
Sand (feels gritty)
( mm, USDA) ( mm, ISSS)
Plate
                              
Silt (feels floury)
( mm, USDA) ( mm, ISSS)
Coin
   
Clay (feels sticky)
(< mm, USDA) (< mm, ISSS)
Barrel
                                     
Sand (feels gritty)
( mm, USDA) ( mm, ISSS)
Plate
                              
Silt (feels floury)
( mm, USDA) ( mm, ISSS)
Coin
   
Clay (feels sticky)
(< mm, USDA) (< mm, ISSS)
     There is disagreement in the scientific community about the exact size ranges of sand and silt. For GLOBE, we will measure sand and silt based on two different size definitions.
Example Sizes:
1. US Department of Agriculture (USDA) which defines the size of:
1. US Department of Agriculture (USDA) which defines the size of:
sand = 2.0 mm mm silt = mm
2. The International Soil Science Society (ISSS) which defines the size of:
sand = 2.0 mm mm silt = mm
2. The International Soil Science Society (ISSS) which defines the size of:
sand = 2.0 mm mm silt = mm
sand = 2.0 mm mm silt = mm
  Clays are the smallest particles and are defined (by both organizations) as being smaller than mm.
  Particles greater than 2.0 mm (sand size) are called stones or gravels and are not considered to be soil material.
  Clays are the smallest particles and are defined (by both organizations) as being smaller than mm.
  Particles greater than 2.0 mm (sand size) are called stones or gravels and are not considered to be soil material.
     
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5. Particle size affects:
Relative Size Comparison of Soil Particles
Relative Size Comparison of Soil Particles
     There is disagreement in the scientific community about the exact size ranges of sand and silt. For GLOBE, we will measure sand and silt based on two different size definitions.
Barrel
                                     
Sand (feels gritty)
( mm, USDA) ( mm, ISSS)
Plate
                              
Silt (feels floury)
( mm, USDA) ( mm, ISSS)
Coin
   
Clay (feels sticky)
(< mm, USDA) (< mm, ISSS)
Barrel
                                     
Sand (feels gritty)
( mm, USDA) ( mm, ISSS)
Plate
                              
Silt (feels floury)
( mm, USDA) ( mm, ISSS)
Coin
   
Clay (feels sticky)
(< mm, USDA) (< mm, ISSS)
     There is disagreement in the scientific community about the exact size ranges of sand and silt. For GLOBE, we will measure sand and silt based on two different size definitions.
Particle size affects:
PERMEABILITY.
How freely water can flow/move through soil is called
AS soil particle size increases, water flow increases meaning that permeability increases.
High permeability means soil CAN’T hold moisture.
1. US Department of Agriculture (USDA) which defines the size of:
1. US Department of Agriculture (USDA) which defines the size of:
sand = 2.0 mm mm silt = mm
2. The International Soil Science Society (ISSS) which defines the size of:
sand = 2.0 mm mm silt = mm
2. The International Soil Science Society (ISSS) which defines the size of:
sand = 2.0 mm mm silt = mm
sand = 2.0 mm mm silt = mm
  Clays are the smallest particles and are defined (by both organizations) as being smaller than mm.
  Particles greater than 2.0 mm (sand size) are called stones or gravels and are not considered to be soil material.
  Clays are the smallest particles and are defined (by both organizations) as being smaller than mm.
  Particles greater than 2.0 mm (sand size) are called stones or gravels and are not considered to be soil material.
     
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6. A way of classifying soil that depends on particle size.
Relative Size Comparison of Soil Particles
Relative Size Comparison of Soil Particles
     There is disagreement in the scientific community about the exact size ranges of sand and silt. For GLOBE, we will measure sand and silt based on two different size definitions.
Barrel
                                     
Sand (feels gritty)
( mm, USDA) ( mm, ISSS)
Plate
                              
Silt (feels floury)
( mm, USDA) ( mm, ISSS)
Coin
   
Clay (feels sticky)
(< mm, USDA) (< mm, ISSS)
Barrel
                                     
Sand (feels gritty)
( mm, USDA) ( mm, ISSS)
Plate
                              
Silt (feels floury)
( mm, USDA) ( mm, ISSS)
Coin
   
Clay (feels sticky)
(< mm, USDA) (< mm, ISSS)
     There is disagreement in the scientific community about the exact size ranges of sand and silt. For GLOBE, we will measure sand and silt based on two different size definitions.
Soil Texture -
A way of classifying soil that depends on particle size.
Examples: loam, sand, clay, silt
Most plants grow best in loam soil = sand/silt/clay
Texture affects the amount of water a soil can hold.
1. US Department of Agriculture (USDA) which defines the size of:
1. US Department of Agriculture (USDA) which defines the size of:
sand = 2.0 mm mm silt = mm
2. The International Soil Science Society (ISSS) which defines the size of:
sand = 2.0 mm mm silt = mm
2. The International Soil Science Society (ISSS) which defines the size of:
sand = 2.0 mm mm silt = mm
sand = 2.0 mm mm silt = mm
  Clays are the smallest particles and are defined (by both organizations) as being smaller than mm.
  Particles greater than 2.0 mm (sand size) are called stones or gravels and are not considered to be soil material.
  Clays are the smallest particles and are defined (by both organizations) as being smaller than mm.
  Particles greater than 2.0 mm (sand size) are called stones or gravels and are not considered to be soil material.
     
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7. Loose soil, like gravel, lets water pass through very easily.
Relative Size Comparison of Soil Particles
Relative Size Comparison of Soil Particles
     There is disagreement in the scientific community about the exact size ranges of sand and silt. For GLOBE, we will measure sand and silt based on two different size definitions.
Barrel
                                     
Sand (feels gritty)
( mm, USDA) ( mm, ISSS)
Plate
                              
Silt (feels floury)
( mm, USDA) ( mm, ISSS)
Coin
   
Clay (feels sticky)
(< mm, USDA) (< mm, ISSS)
Barrel
                                     
Sand (feels gritty)
( mm, USDA) ( mm, ISSS)
Plate
                              
Silt (feels floury)
( mm, USDA) ( mm, ISSS)
Coin
   
Clay (feels sticky)
(< mm, USDA) (< mm, ISSS)
     There is disagreement in the scientific community about the exact size ranges of sand and silt. For GLOBE, we will measure sand and silt based on two different size definitions.
Packed soil, like red clay, does not let water move through very easily.
One grain of clay is SUPER small.
Loose soil, like gravel, lets water pass through very easily.
One grain of gravel is a BIG rock.
1. US Department of Agriculture (USDA) which defines the size of:
1. US Department of Agriculture (USDA) which defines the size of:
sand = 2.0 mm mm silt = mm
2. The International Soil Science Society (ISSS) which defines the size of:
sand = 2.0 mm mm silt = mm
2. The International Soil Science Society (ISSS) which defines the size of:
sand = 2.0 mm mm silt = mm
sand = 2.0 mm mm silt = mm
  Clays are the smallest particles and are defined (by both organizations) as being smaller than mm.
  Particles greater than 2.0 mm (sand size) are called stones or gravels and are not considered to be soil material.
  Clays are the smallest particles and are defined (by both organizations) as being smaller than mm.
  Particles greater than 2.0 mm (sand size) are called stones or gravels and are not considered to be soil material.
     
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8. Soils can be basic or acidic.
Relative Size Comparison of Soil Particles
Relative Size Comparison of Soil Particles
     There is disagreement in the scientific community about the exact size ranges of sand and silt. For GLOBE, we will measure sand and silt based on two different size definitions.
Barrel
                                     
Sand (feels gritty)
( mm, USDA) ( mm, ISSS)
Plate
                              
Silt (feels floury)
( mm, USDA) ( mm, ISSS)
Coin
   
Clay (feels sticky)
(< mm, USDA) (< mm, ISSS)
Barrel
                                     
Sand (feels gritty)
( mm, USDA) ( mm, ISSS)
Plate
                              
Silt (feels floury)
( mm, USDA) ( mm, ISSS)
Coin
   
Clay (feels sticky)
(< mm, USDA) (< mm, ISSS)
     There is disagreement in the scientific community about the exact size ranges of sand and silt. For GLOBE, we will measure sand and silt based on two different size definitions.
pH of Soil -
Soils can be basic or acidic.
Most plants grow best in soils with a pH between 5-7
If soil is too acidic, lime can be added to make it more basic.
1. US Department of Agriculture (USDA) which defines the size of:
1. US Department of Agriculture (USDA) which defines the size of:
sand = 2.0 mm mm silt = mm
2. The International Soil Science Society (ISSS) which defines the size of:
sand = 2.0 mm mm silt = mm
2. The International Soil Science Society (ISSS) which defines the size of:
sand = 2.0 mm mm silt = mm
sand = 2.0 mm mm silt = mm
  Clays are the smallest particles and are defined (by both organizations) as being smaller than mm.
  Particles greater than 2.0 mm (sand size) are called stones or gravels and are not considered to be soil material.
  Clays are the smallest particles and are defined (by both organizations) as being smaller than mm.
  Particles greater than 2.0 mm (sand size) are called stones or gravels and are not considered to be soil material.
     
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9. Soil Formation:
Soil forms as rock is broken down by weathering and then mixes with other materials on the surface of Earth’s crust.
Types of weathering: heat, cold, water (rain) and yes, air (O2 and CO2).

10. How do rocks break into smaller pieces?
Freezing and thawing breaks apart bedrock
Plant roots wedge between rocks and break them
Acid rain/chemicals break down rocks
Animals help grind rock into smaller pieces.
Break down of dead organisms add to the mixture.

11. Nutrient Depletion: Erosion: Soil becomes less fertile –
If farmers replant crops over and over with out fertilizing soil, the crops use nutrients faster than decomposers can supply.
Erosion:
Movement of rock and soil by wind, water and gravity.

12. Are all soils the same?
Soil type affects which type of plants/animals can live there.
Factors that affect soil type are:
Types of plants
Climate
Time
Slope of the land