how soil forms. what is soil? soil is the loose, weathered material on earth’s surface in which...
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![Page 1: How Soil Forms. What is Soil? Soil is the loose, weathered material on Earth’s surface in which plants grow. One of the main ingredients of soil is: Bedrock](https://reader036.vdocuments.us/reader036/viewer/2022062517/56649f305503460f94c4b1ec/html5/thumbnails/1.jpg)
How Soil FormsHow Soil Forms
![Page 2: How Soil Forms. What is Soil? Soil is the loose, weathered material on Earth’s surface in which plants grow. One of the main ingredients of soil is: Bedrock](https://reader036.vdocuments.us/reader036/viewer/2022062517/56649f305503460f94c4b1ec/html5/thumbnails/2.jpg)
What is Soil?What is Soil?
• Soil is the loose, weathered material on Earth’s surface in which plants grow.
One of the main ingredients of soil is:• Bedrock which is the solid layer of rock beneath the soil.
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Soil Composition
• Soil is comprised of a mixture of rock, particles, minerals, decayed organic material, water and air.
• The decayed organic material in soil is called humus. Humus provides plants with the nutrients they need to grow.
• Soil that is rich in humus has a high fertility rate supporting plant growth.
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Soil Texture
• Soil texture depends on the size of the individual particles.
• The largest particle size is gravel.
• The smallest particle size is clay.
• Loam is the best type of soil for growing plants since it is made up of about equal parts of clay, sand and silt.
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Soil Particle SizeSoil Particle Size
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The Process of Soil FormationThe Process of Soil Formation
• Soil forms as rock is broken down by weathering and mixes with other materials.
• 3 horizons (layers)– A horizon: topsoil– B horizon: subsoil– C horizon: partly
weathered rock
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Horizon A
• Horizon A is made up of topsoil.
• Topsoil is a crumbly, dark brown soil that is a mixture of humus, clay and other materials.
• This soil horizon is most
important for growing food.
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Horizon B
• Horizon B is consists of clay and other particles washed down from Horizon A; very little humus.
• Horizon B is often called subsoil.
• Horizon B forms last as particles
wash down from the A horizon.
![Page 9: How Soil Forms. What is Soil? Soil is the loose, weathered material on Earth’s surface in which plants grow. One of the main ingredients of soil is: Bedrock](https://reader036.vdocuments.us/reader036/viewer/2022062517/56649f305503460f94c4b1ec/html5/thumbnails/9.jpg)
Horizon C
• Horizon C is weathered rock.
• The C horizon is most similar to bedrock.
• It consists mostly of pieces of bedrock.
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Rate of Soil Formation
• The rate of soil formation depends on the climate and type of rock.
• Weather occurs most rapidly in areas with a warm, rainy climate so soil will form faster in these areas.
• Soil forms more quickly from limestone than granite since limestone weathers faster.
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Soil TypesSoil Types
• Classified based on climate, plants and soil composition
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Types of Soil
• Fertile soil forms in regions with hot, wet climates.
• Thin soil forms in mountains and polar regions with cold and dry climates.
• The thickest and most fertile soil forms in moderate temperatures with moderate rainfall.
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Major soil types in North America
• Forest
• Prairie
• Desert
• Mountain
• Tundra
• Tropical
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Living Organisms in SoilLiving Organisms in Soil
• Two ways organisms contribute to soil:
A. Forming Humus
B. Mixing the Soil
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Forming Humus• Plants contribute most of the organic remains
that form humus.• As plants shed leaves, they form a loose layer
called litter.• Humus forms in a process known as
decomposition where organisms that live in the soil turn dead organic material into humus.
• Decomposers are the organisms that break down the remains. These include fungi, bacteria, worms, and other organisms.
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Mixing the SoilMixing the Soil
• Earthworms mix humus with other materials in soil.
• They also help move air and water into the soil through a process called aeration.