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

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.

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.

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) (2.00 - 0.05 mm, USDA) (2.00 - 0.02 mm, ISSS) Plate                                Silt (feels floury) (0.05 - 0.002 mm, USDA) (0.02 - 0.002 mm, ISSS) Coin     Clay (feels sticky) (< 0.002 mm, USDA) (< 0.002 mm, ISSS) Barrel                                       Sand (feels gritty) (2.00 - 0.05 mm, USDA) (2.00 - 0.02 mm, ISSS) Plate                                Silt (feels floury) (0.05 - 0.002 mm, USDA) (0.02 - 0.002 mm, ISSS) Coin     Clay (feels sticky) (< 0.002 mm, USDA) (< 0.002 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 - 0.05 mm silt = 0.05 - 0.002 mm 2. The International Soil Science Society (ISSS) which defines the size of: sand = 2.0 mm - 0.05 mm silt = 0.05 - 0.002 mm 2. The International Soil Science Society (ISSS) which defines the size of: sand = 2.0 mm - 0.02 mm silt = 0.05 - 0.002 mm sand = 2.0 mm - 0.02 mm silt = 0.05 - 0.002 mm   Clays are the smallest particles and are defined (by both organizations) as being smaller than 0.002 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 0.002 mm.   Particles greater than 2.0 mm (sand size) are called stones or gravels and are not considered to be soil material.       Previous Next Top       Previous Next Top    

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) (2.00 - 0.05 mm, USDA) (2.00 - 0.02 mm, ISSS) Plate                                Silt (feels floury) (0.05 - 0.002 mm, USDA) (0.02 - 0.002 mm, ISSS) Coin     Clay (feels sticky) (< 0.002 mm, USDA) (< 0.002 mm, ISSS) Barrel                                       Sand (feels gritty) (2.00 - 0.05 mm, USDA) (2.00 - 0.02 mm, ISSS) Plate                                Silt (feels floury) (0.05 - 0.002 mm, USDA) (0.02 - 0.002 mm, ISSS) Coin     Clay (feels sticky) (< 0.002 mm, USDA) (< 0.002 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 - 0.05 mm silt = 0.05 - 0.002 mm 2. The International Soil Science Society (ISSS) which defines the size of: sand = 2.0 mm - 0.05 mm silt = 0.05 - 0.002 mm 2. The International Soil Science Society (ISSS) which defines the size of: sand = 2.0 mm - 0.02 mm silt = 0.05 - 0.002 mm sand = 2.0 mm - 0.02 mm silt = 0.05 - 0.002 mm   Clays are the smallest particles and are defined (by both organizations) as being smaller than 0.002 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 0.002 mm.   Particles greater than 2.0 mm (sand size) are called stones or gravels and are not considered to be soil material.       Previous Next Top       Previous Next Top    

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) (2.00 - 0.05 mm, USDA) (2.00 - 0.02 mm, ISSS) Plate                                Silt (feels floury) (0.05 - 0.002 mm, USDA) (0.02 - 0.002 mm, ISSS) Coin     Clay (feels sticky) (< 0.002 mm, USDA) (< 0.002 mm, ISSS) Barrel                                       Sand (feels gritty) (2.00 - 0.05 mm, USDA) (2.00 - 0.02 mm, ISSS) Plate                                Silt (feels floury) (0.05 - 0.002 mm, USDA) (0.02 - 0.002 mm, ISSS) Coin     Clay (feels sticky) (< 0.002 mm, USDA) (< 0.002 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 - 0.05 mm silt = 0.05 - 0.002 mm 2. The International Soil Science Society (ISSS) which defines the size of: sand = 2.0 mm - 0.05 mm silt = 0.05 - 0.002 mm 2. The International Soil Science Society (ISSS) which defines the size of: sand = 2.0 mm - 0.02 mm silt = 0.05 - 0.002 mm sand = 2.0 mm - 0.02 mm silt = 0.05 - 0.002 mm   Clays are the smallest particles and are defined (by both organizations) as being smaller than 0.002 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 0.002 mm.   Particles greater than 2.0 mm (sand size) are called stones or gravels and are not considered to be soil material.       Previous Next Top       Previous Next Top    

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) (2.00 - 0.05 mm, USDA) (2.00 - 0.02 mm, ISSS) Plate                                Silt (feels floury) (0.05 - 0.002 mm, USDA) (0.02 - 0.002 mm, ISSS) Coin     Clay (feels sticky) (< 0.002 mm, USDA) (< 0.002 mm, ISSS) Barrel                                       Sand (feels gritty) (2.00 - 0.05 mm, USDA) (2.00 - 0.02 mm, ISSS) Plate                                Silt (feels floury) (0.05 - 0.002 mm, USDA) (0.02 - 0.002 mm, ISSS) Coin     Clay (feels sticky) (< 0.002 mm, USDA) (< 0.002 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 - 0.05 mm silt = 0.05 - 0.002 mm 2. The International Soil Science Society (ISSS) which defines the size of: sand = 2.0 mm - 0.05 mm silt = 0.05 - 0.002 mm 2. The International Soil Science Society (ISSS) which defines the size of: sand = 2.0 mm - 0.02 mm silt = 0.05 - 0.002 mm sand = 2.0 mm - 0.02 mm silt = 0.05 - 0.002 mm   Clays are the smallest particles and are defined (by both organizations) as being smaller than 0.002 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 0.002 mm.   Particles greater than 2.0 mm (sand size) are called stones or gravels and are not considered to be soil material.       Previous Next Top       Previous Next Top    

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) (2.00 - 0.05 mm, USDA) (2.00 - 0.02 mm, ISSS) Plate                                Silt (feels floury) (0.05 - 0.002 mm, USDA) (0.02 - 0.002 mm, ISSS) Coin     Clay (feels sticky) (< 0.002 mm, USDA) (< 0.002 mm, ISSS) Barrel                                       Sand (feels gritty) (2.00 - 0.05 mm, USDA) (2.00 - 0.02 mm, ISSS) Plate                                Silt (feels floury) (0.05 - 0.002 mm, USDA) (0.02 - 0.002 mm, ISSS) Coin     Clay (feels sticky) (< 0.002 mm, USDA) (< 0.002 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 - 0.05 mm silt = 0.05 - 0.002 mm 2. The International Soil Science Society (ISSS) which defines the size of: sand = 2.0 mm - 0.05 mm silt = 0.05 - 0.002 mm 2. The International Soil Science Society (ISSS) which defines the size of: sand = 2.0 mm - 0.02 mm silt = 0.05 - 0.002 mm sand = 2.0 mm - 0.02 mm silt = 0.05 - 0.002 mm   Clays are the smallest particles and are defined (by both organizations) as being smaller than 0.002 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 0.002 mm.   Particles greater than 2.0 mm (sand size) are called stones or gravels and are not considered to be soil material.       Previous Next Top       Previous Next Top    

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).

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.

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.

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