Download Soil Horizons Questions

the C horizon form the basic structure of soil.
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Soil Horizons
By Cindy Grigg
Soil covers Earth's land. It is a vital natural
resource. Soil is a thin layer in which plants
can grow.
Soil is not all the same. It has different
layers. The layer on top is made of humus
(HYOO-muss). Humus is dark brown or
black. It is made of the remains of plants
and animals that were once alive. As leaves
and other remains rot, they become part of
soil underneath. This top layer is called the
O horizon. O stands for organic. Organic
matter came from living things. This layer
is not really soil. It is plant and animal matter on top of the soil. It
may be only about one or two inches deep. The O horizon is "O" so
important for having healthy soil.
The second layer from the top is called the A horizon. It is a mixture
of humus, air, water, and small bits of minerals. It is dark colored, too,
but not as black as the O hoizon. People often call this layer "topsoil."
It is the top layer of soil. In the A horizon, you will find plant roots.
Living things like earthworms, ants, and beetles make their homes
here. Microorganisms like bacteria and fungi are found here, too.
Microorganisms are too small to see without a microscope. They
break down, or decompose, organic materials. They are important to
healthy soil. This layer can be eight to twelve inches thick. The A
horizon is "A" home to living things.
The third layer is called the B horizon. It is often brown or
reddish-colored. It has little, if any, humus and living organisms.
Longer plant roots can be found in this layer. It is full of minerals. It is
often called "subsoil." It lies "B"-low the topsoil.
The next layer is called the C horizon. It comes after A and B. It is
made of big, broken rocks. Some of them weathered from the layer of
bedrock below the C horizon. Others were carried by erosion and
deposited there. C is the parent of the layers above it. The minerals in
Below the C horizon is bedrock, sometimes called the R horizon. R is
for solid rock, and it is the base that the soil layers sit upon.
A slice of soil can show the different soil horizons. This is called a
soil profile. A soil profile looks a little like a piece of a layer cake.
The depth of each layer can be easily measured. In some soils, the
different layers are easy to see. They almost look as though someone
drew a line between them. In others, one layer blends into the next. It
can be hard to say where one layer ends and the next one begins.
Making a soil profile is helpful for soil management. The profile can
show the depth of each layer and the parent material underneath. It
can show what minerals are present. Then it can be decided what the
soil might need added to it in order to grow a certain type of plant.
Not all layers are in every soil profile. Soil is affected by weather and
climate. Erosion affects soil, too. Soil is a mixture of rocks, minerals,
and organic matter. Soil can be very different in different places. The
composition or makeup of soil affects the kinds of plants that can
grow in it.
Soil Horizons
Questions
1. Which of these is NOT soil?
A. A horizon
B. B horizon
C. C horizon
D. R horizon
E. all of the above
2. Which of these means about the same as the word
"composition" as it was used in the last sentence of the story?
A. an artistic creation
B. the parts of a mixture
C. putting together
D. a piece of writing
Examine soil in different areas. Write a paragraph describing each
soil sample. Describe the color and texture. Can you tell what the
different pieces are that make up the soil? If so, identify as many
parts as you can.
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3. Which layer would you find nearest the surface?
A. R horizon
B. Q horizon
C. B horizon
D. O horizon
E. C horizon
4. Which layer would you find farthest from the surface?
A. C horizon
B. O horizon
C. A horizon
D. B horizon
5. A soil profile looks a little like a piece of a layer cake. This
sentence is:
A. a simile
B. a metaphor
C. onomatopoeia
D. hyperbole
6. The story says that the composition or makeup of soil affects
the kinds of plants that can grow in it. Which of these
statements is probably true?
A. The composition of the soil also affects what animals can
live in different places.
B. The composition of soil could not affect the animals that
live there.
C. Soil profiles are not helpful for soil management.
7. Soil is a ______ of rocks, minerals, and organic matter.
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Why do you think that people should know about soil? In what ways
is soil useful?