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The soil
Soil is the layer of loose material on Earth's land surface and is made up of particles of rock, air, water, and humus. Soil is organized into layers with topsoil at the surface containing the most humus and nutrients for plant growth, subsoil below it containing some humus and rock particles, and bedrock forming the bottom layer underneath. Soil types vary depending on the amounts of sand, silt, and clay particles in them, with loam being an ideal mixture supporting plant growth.
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Defines soil and its significance as a material that supports life on Earth.
Describes the role of soil for living organisms and its necessity for plant growth and food production.
Outlines the four main substances in soil: particles, air, water, and humus, highlighting humus's nutrient role.
Introduces the concept of soil layers and how they vary in thickness and color across different locations.
Details the topsoil layer, its dark color due to humus, and its habitat for various animals.
Describes subsoil as lighter in color with fewer nutrients, including broken rocks and tree roots.
Explains bedrock's role in soil development as it breaks down to contribute to new soil.
Discusses the diversity of soil types and the role of rock particles in differentiating soils.
Identifies three soil particles: sand, silt, clay, and explains loam as a mixture containing all.
Describes sandy soil's properties: rough texture, quick drainage, and limitations for plant roots.
Highlights silt's medium particle size, slippery texture, and its ability to retain water better than sand.
Elaborates on clay's small particle size, smooth texture, and risks of water retention for plant growth.
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The soil
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- 2. Parts of soil Many living things depend on soil. Soil is the layer of loose material that covers most of Earth`s land. Soil has the materials plants need to grow. People need healthy soil to grow food.
- 3. All soil hasthe same four substances. Particles are tiny pieces of rock make up most of the soil. They come from larger rocks that have broken apart. Air. water. 1 2 3
- 4. Humus is madeof the 4 remains of plants and animals that were once alive. As plant and animal remains in humus decay, or break down or rot, nutrients are released. A nutrient is a substance needed by living things for energy and growth.
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- 6. Soil is organizedinto layers. Different places have soil layers of different thicknesses and color.
- 7. Topsoil Topsoil isthe top layer. Topsoil is the darkest layer because it contains the most humus.
- 8. Animals such asworms, spiders, and insects also makes their homes in topsoil. Humus contains much of what plants need to grow.
- 9. subsoil Subsoil isunder topsoil. It is lighter in color than topsoil. It does not have as much humus as topsoil. Subsoil includes pieces of broken rocks. Tree roots grow into the subsoil. Water from precipitation may be in this layer.
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- 11. Bedrock Bedrock isbelow subsoil. As this rock breaks down, it provides resources for making new soil.
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- 13. Soil is notthe same everywhere. Part of what makes soils different is the types of rock particles each soil contains. The three types of particles: sand slit clay
- 14. Most soils area mix of sand, slit, and clay. Loam is the mixture of sand, slit, and clay. Loam also contains air, water, and humus.
- 15. Sand Sand haslarge rock particles. Sandy soil feels rough and gritty. Water passes quickly through it. Plant roots may not be able to soak up water fast enough in sandy soil.
- 16. silt Silt hasmedium-sized particles that are packed together. Wet silt feels slippery and smooth. Although water passes through it, slit soil holds water better than sand.
- 17. clay Clay particlesare the smallest. Wet clay feels smooth and sticky. Clay holds water so well that plants growing in it may ``drown`` if roots cannot get the air they need.