Name ______________________________________ Date _________
TEKS Review
4.7A
TEKS 4.7A examine properties of soils, including color and texture, capacity to retain water, and
ability to support the growth of plants
Properties of Soil
What Is Soil?
Soil Layers and Formation
Soil may be referred to as dirt, mud,
muck, earth, clay, silt, or sand. There are so
many words for soil because there are so
many different kinds of soil. The soil in one
place can be very different than the soil less
than a kilometer away. In the United States
alone, there are more than 70,000 different
kinds of soil! No matter how different soils
are, they all have some similarities. Soil is a
mixture of small bits of weathered rocks,
minerals, water, and the decaying remains of
once-living things.
You’ve learned that weathering is the
process of breaking down rocks into smaller
pieces. All soils form from weathered rock.
Soil can form from the weathered rock right
under it, or it can form from eroded sediment
carried from far away.
One of the main components of soil is
humus. Humus is the part of soil made up of
dead plants and animals. For example, when a
tree loses a leaf, the leaf falls to the ground.
As decomposers break the leaf down into
smaller parts, it becomes humus.
You might not think of soil as a resource,
but it is a very important one. Without soil,
plants couldn’t grow and many animals would
not have a place to live. Some soils are used in
manufacturing processes. For example, some
soils can be used to make bricks or other
building materials.
This pot is made of a
type of soil called clay.
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If you dig down into soil, you would find
that it is made of up several layers. Each layer
has different properties. The top layer is called
topsoil. This is the layer in which most
biological activity occurs. Animals, plants,
fungi, and bacteria all live here. If you dig
down far enough, you would find bedrock.
Bedrock is solid, unweathered rock that lies
beneath the loose surface deposits of soil.
Soils form in
layers. Each layer
has different
characteristics.
topsoil
bedrock
TEKS 4.7A
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Name ______________________________________ Date _________
TEKS Review
4.7A
Soil Color
The most obvious property when looking
at soil is its color. The color of soil can tell
scientists a lot about it. Geologists officially
recognize more than 170 different soil colors.
Most of these are shades of black, brown, red,
gray, and white.
Many types of soil, called loam, have a
mixture of sand, silt, and clay particles. Wellbalanced soils are the best ones to support
plant growth. Farms are often built on
locations with loam.
In general, the darker a soil, the more
nutrient-rich it is. The darker color often
indicates a high amount of humus. Gray soils
often have poor drainage, and red soils are
usually very undeveloped, poor soils.
These general rules about soil colors can,
however, be misleading. Under certain
conditions, a very poor soil can be dark black,
while a rich, healthy soil can look red.
Soil Texture
Another property of soil is its texture.
Pick up a pinch of soil between your fingers,
and rub it back and forth. You will quickly
notice that the soil is made up of many
different-size particles. These particles give
the soil its texture.
Soil texture refers to the relative
proportion of sand, silt, and clay in a sample
of soil. These particles differ in size. Sand
particles are the largest, silt particles are
medium-sized, and clay particles are tiny.
Pure clay feels smooth when you rub it
between your hands.
Particle Size in Soils
Particle
Particle Size
clay
less than 0.002 mm
silt
0.002 mm–0.05 mm
sand
greater than 0.05 mm
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Soil Structure
The mixture of particle sizes in a soil
affects many other properties, including how
much water it can hold and how fast water
drains through it. Soils have different amounts
of open space, called pores, between particles.
Pores can also be filled with water. Soils with
larger pore spaces can hold more water.
Permeability refers to how quickly water
drains into or moves through a soil. This speed
depends on how large the soil pores are. A
highly permeable soil is one in which water
runs though it quite easily. Sandy soils have
large, well-connected pore spaces and high
permeability. Water does not move through
clay soils easily.
Nutrients
Because soils are made from rocks, they
contain minerals. The kinds of minerals found
in any soil depend on the kind of rock from
which the soil formed. Certain minerals are
needed for plant growth.
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TEKS Review
4.7A
Name ______________________________________ Date _________
In order for plants to obtain the nutrients
they need to survive, nutrients must be carried
into them. This happens as nutrients are
dissolved into the groundwater that the plants
absorb through their roots. As humus decays,
it adds organic matter in the form of humus to
the soil. Humus improves soil moisture
retention while affecting soil chemistry.
If a soil has too much acid in it, it is said
to be acidic. In this kind of soil, the nutrients
in the soil are dissolved too quickly and wash
away as the water drains. If a soil is too
alkaline—if there is not enough acid—then
nutrients will not dissolve quickly enough.
Thus, a neutral soil, which is neither too
acidic nor too alkaline, is the best kind of soil
for plants.
Materials
Hands-On Activity
Soils Hold Water
There are many properties of soil that you can examine. In this
activity, you will measure how well two types of soil hold water.
Procedure:
•
•
•
•
•
•
•
•
•
potting soil
sand
measuring cup
coffee filter
2 funnels
2 ring stands
water
2 beakers
graduated cylinder
1. Place a funnel in each ring stand, and place a coffee filter inside each funnel.
Put a beaker beneath the funnel.
2. Fill one of the filters with potting soil. Measure the volume of soil you add.
3. Add the same amount of sand to the other filter.
4. Put 200 mL of water into a graduated cylinder. Slowly pour the water into the
potting soil. Stop as soon as you see water dripping from the bottom of the funnel.
Record how much water the soil held.
5. Repeat Step 4 with the sand.
Discussion Questions:
1. How do the two types of soil compare?
2. Where can you infer the water poured into the soil went?
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TEKS 4.7A
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TEKS Review
4.7A
Name ______________________________________ Date _________
Hands-On Activity
Materials
Soils and Plant Growth
Are the soils in your area good for growing plants? Does soil type
affect how well a plant grows? You will answers these questions
in this investigation.
Procedure:
• at least 3 soil
samples
• gloves and goggles
• measuring cup
• planting pots
• water
• seeds
1. With a trusted adult, collect a sample of soil and label the location where it
was collected. Bring it into the class and share the sample with your group.
2. Analyze each soil sample. Record properties of the soil, including the soil’s
color and texture. Determine texture by rubbing the soil between your fingers
and by observing it with a hand lens.
3. Measure enough soil to fill a planting pot half way. Add a few seeds,
and cover them with another inch of soil. Label the pot.
4. Repeat Steps 2 and 3 with the soil samples from the other members of your group.
Be sure to keep the amount of soil and number of seeds used constant.
5. Over the next few weeks, add water to the pots as they dry out. All of the
pots need to receive the same amount of water. Record how well the plants
grow. You could record the number of leaves or the height of the plants.
6. Evaluate your results and compare them with your analysis of the soil samples.
As a group, come up with a scientific explanation.
Discussion Questions:
1. How well did the plants grow in each type of soil?
2. How did you control variables in this experiment?
3. Describe the process your group used to come up with
an explanation you all agreed on.
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TEKS 4.7A
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Name ______________________________________ Date _________
TEKS Review
4.7A
Properties of Soil
List the three particle sizes that make up soil in order from smallest to largest.
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What do plants obtain from soil?
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How does the texture of clay differ from the texture of sand?
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Draw what the soil near your home looks like through a hand lens. Label any parts you can.
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TEKS 4.7A
Page 5 of 7
Name ______________________________________ Date _________
TEKS Review
4.7A
TEKS Assessment 4.7A
Fill in the letter of the best choice.
Soil is made up of four main ingredients.
Choose the correct list of ingredients.
Use the drawing below to answer
questions 5 and 6.
tiny pieces of rock; humus; air;
sand
humus, or dead plant material; clay;
water; salts
tiny pieces of rock; air; water;
humus or dead plant material
A
B
C
air; water; tiny pieces of rock;
manure
D
Which type of soil dries out quickly after
a rainstorm?
Which label points to bedrock?
clay soil
loam
A
silty soil
B
sandy soil
C
D
Which soil ingredient is made of
decayed plants and animals?
Which label points to the layer where
you would expect to find the most
humus?
air
humus
A
minerals
B
water
C
D
Which type of soil feels the smoothest
when you rub it between your fingers?
loam
clay
silt
sand
TEKS Review and Assessment
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TEKS 4.7A
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Name ______________________________________ Date _________
TEKS Review
4.7A
Answer Key
Hands-On Activity (p. 3)
1. Students should find that the potting soil held more water than the sand.
2. Water that was poured into the soil filled the spaces between the pores.
Hands-On Activity (p. 4)
1. Answers will vary but should be based on observations and measurements.
2. Sample answer: I controlled variables by ensuring that the only difference between the
pots was the type of soil in the pots. All other variables, including the number of seeds,
the amount of water added to each pot, and the amount of light the plants received, were
controlled (kept constant).
3. Sample answer: We discussed our data and compared our results. We used logic to
eliminate explanations that didn’t make sense. We discussed what inferences and
conclusions we all agreed on, then we debated those we didn’t agree on.
Student Response Activity (p. 5)
1. clay; silt; sand
2. Plants obtain water and nutrients from soil.
3. Clay feels smooth when you rub it between your fingers. Sand feels gritty. You can feel
the individual particles of sand. The clay particles are too small for you to feel them
individually.
4. Check students’ drawings. Provide soil samples for those students who are unable to obtain
them at home.
TEKS Assessment (p. 6)
1. C
2. D
3. B
4. B
5. D
6. A
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TEKS 4.7A
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