What is 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.

Parts of soil

All soil has the 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.

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2

3

Humus is made of the 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.

4

Soil layers

Soil is organized into layers.Different places have soil layers of different thicknesses and color.

Topsoil is the top layer. Topsoil is the darkest layer because it contains the most humus.

Topsoil

Animals such as worms, spiders, and insects also makes their homes in topsoil. Humus contains much of what plants need to grow.

Subsoil is under 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.

subsoil

Subsoil

Bedrock is below subsoil. As this rock breaks down, it provides resources for making new soil.

Bedrock

Kinds of soil

Soil is not the 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

Most soils are a mix of sand, slit, and clay.

Loam is the mixture of sand, slit, and clay.

Loam also contains air, water, and humus.

Sand has large 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.

Sand

Silt has medium-sized particles that are packed together. Wet silt feels slippery and smooth. Although water passes through it, slit soil holds water better than sand.

silt

Clay particles are 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.

clay