Download Study Guide for Soil Key

Soil Quiz Study Guide Answer Key
1. What is soil? A mixture of rock particles, humus, water, and air.
What is a soil profile? The soil horizons from a specific location
2. What is a soil horizon? A layer of soil with properties that differ from those of the layer above or below it
3. What is humus? The decayed organic matter in soil
Why is it important to have humus in soil? Humus provides nutrients for the plant
4. What is the relationship between rocks, soil, and the environment?
The kind of soil that is formed depends on the type of rocks and the climate found in the environment.
 The rocks found in the environment will weather into the rock particles that will become part of the
soil. For example, sandstone will weather into particles of sandy which will form a sandy type of soil.
 The climate of an environment is hugely influenced by temperature and rainfall/precipitation .
Water availability and temperature will determine the type and amount of plants and animals found
in the environment. Temperature is a big factor in how fast the decay of the plants and animals
found in the environment will form humus.
5. What role does climate play in the kind soil that is formed? Hint: think why tropical, desert, temperate, and
arctic soils have different characteristics. ( refer to page 125 A for soil formation in these climate regions) As
stated above, temperature and rainfall determine the type and amount of plants and animals that can live
in a particular climate. Plants are adapted to temperature and rainfall ranges. The colder climates get, the
fewer the numbers and varieties of plants will be. The drier the climates get, the fewer the plants,
regardless of the temperature. Temperature also determines how fast decay can happen to the plants that
exist in that climate. The more plentiful the plants and the faster the decay, the more humus is formed and
the richer the soil will be.
Temperature and rainfall also influence how fast rock will weather into the rock particles necessary for soil
formation. Both mechanical and chemical weathering are much slower in cold, dry climates. They are also
slow in hot dry climates. That makes for large rocks and rocky soil. Rock particles contain minerals that
plants need to grow and stay healthy.
5. Describe how soil is formed. Soil is formed over time when rocks are weathered down into small particles,
plants and other organic matter decay, and water and air are mixed in. Other factors in soil formation
include climate, landforms and the action of living things. Living things like microorganisms break down
dead plants and animals to form humus, produce acid that breaks down rocks, and fix nitrogen from the air
into the soil so that plant roots can absorb it. Animals that burrow in the soil help water and air mix in.
About how long does it take for nature to make one inch of topsoil? It takes a very long time from a hundred
years to thousands of years, depending on the climate. (Soil Society of America. Org)
6. Explain why weathering and erosion are not the same thing. Weathering is the breaking down of rock into
smaller pieces. Erosion is the process of moving the rock pieces from one place to another by water, wind,
and/or ice.
7. Sediment is smaller pieces of rock that are carried by water or by air and have settled on the bottom of a
body of water or on the ground.
8. The deeper you go into a soil profile, the lighter the color will be.
9. As much as 50% of soil could be made up of air and water.
10. Which horizon would be the best for plant growth? Horizon A Explain why: It contains the most humus,
air and water.
11. Follow the instructions to complete the soil diagram:
Diagram:
1. Label the soil profile below with the horizon letter and the name!
2. Write what each layer contains.
3. Shade each layer with the correct color.
Litter : not a layer of soil
contains grass, plants, and animals
Horizon O___
Topsoil: 1st layer of soil
contains humus, plant roots, small animals, water, nutrients
A
Horizon ___
Subsoil: 2nd layer of soil
contains limited plant growth, fewer nutrients and water
B
Horizon ___
Parent Material: 3rd layer of soil
contains only weathered rock and sediment
Bedrock: not a layer of soil
contains only solid rock
C
Horizon ___
R
Horizon ___
12. Be able to answer questions about soil horizons. Some examples of such questions (and these are not
all!):
a. In which layer would you find organic matter? Horizon A, topsoil, has the most organic matter. Horizon B,
subsoil, has a little organic matter.
b. Which two layers are not really soil? Horizon O: litter, and R: bedrock. Why aren’t they considered to be
soil? They do not fit the definition of soil because they are not mixtures of humus, rock particles, air and
water. Then why are they included in a soil profile? Litter contributes organic matter that will eventually
become humus. Bedrock contributes the rock that will eventually become the rock particles that will
determine the kind of minerals the soil will have.
c. What makes the A horizon the darkest in color? Humus- decayed organic matter
d. Which layer of soil consists of weathered rock and sediment? Horizon C, Parent material
e. And what, exactly, is sediment? Sediment is smaller pieces of rock that are carried by water or by air and
have settled on the bottom of a body of water or on the ground.
13. Why is soil a necessary resource? It provides nutrients necessary for plant life. Plants are the base of the
food chain on Earth’s surface.
14. Why is it important to conserve soil? It takes nature so very long to make just one inch of topsoil to
replace whatever gets used up or carried away.
15. What can happen to soil as a result of construction and development? Construction and development
remove the ground cover that holds soil in place. It is easily eroded and muddies rivers and streams.
16. A farmer notices that his crops are being destroyed by wind. They are starting to lean to one side, and the
soil is blowing across the field. What can he do to better conserve the soil? Explain & draw a picture.
He should plant rows of trees between his fields to serve as windbreaks. They will reduce the force of the
winds that can blow the soil away.
Trees used as WINDBREAKS
17. A neighbor of yours is getting ready to plant a garden of flowers in his backyard. He asks you for ideas on
how to conserve soil. You notice that his backyard has a lot of hills. What do you suggest? Explain & draw a
picture. He could plant the flowers in terraces. He could also plant them in rows, contour plowing, that
follow the curves of the hill instead of straight up and down. This will slow rainwater runoff that would
erode the soil.
Terraces
Contour Plowing
18. Your grandmother has had a farm for 20 years. Each year she plants potatoes on the left field. This year,
half of her potatoes died. What should she do next year? Explain & draw a picture.
She should not plant potatoes again. Instead she should plant something else that does not take the same
nutrients that potatoes would take from the soil. She should plant some kind of beans which would actually
restore nitrogen, a necessary plant nutrient, instead of potatoes. Planting different crops on the same field
in different years helps maintain soil fertility. This practice is called crop rotation.
19. What is fertility? The state of capacity for abundant productivity. When thinking about soil, what would
fertility mean? It would mean the ability to maintain and support a lot of plants which can produce a large
amount of food for people and animals.
20. What does the term, pH mean? power of the Hydrogen ion. The number with the pH tells us how acidic
or how alkaline a substance is. A pH of 0 is the most acidic, a pH of 7 is neutral, and a pH of 14 is the most
alkaline or basic.