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.

1. What is
soil?

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 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

4. Humus is made of the
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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.

5. Soil
layers

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

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

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

9. subsoil
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.

10. Subsoil

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

12. Kinds of soil

13. 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

14. 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.

15. Sand
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.

16. silt
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.

17. clay
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.