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Activity 2: Grades 5-8
Nutrient Depletion |
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As
you learned in "Thos.
Jefferson, Slavemaster," In the late 1700's, the
role of the field slave evolved as landowners shifted from
tobacco to wheat cultivation. Once a lucrative crop, tobacco
gradually became a less and less profitable crop, in part
because harvesting tobacco year after year stripped the soil
of nutrients. When the concept of crop rotation was introduced,
the plantation soils regained some lost vitality.
All plants require nutrients to grow and thrive. These nutrients
are found in the soil and absorbed through the plants' root
systems. Dissolved in water, the nutrients are distributed
throughout the plant via its system of water carrying vessels.
When the plants are harvested, they take the nutrients with
them and the soil becomes depleted of these essential components.
In this activity, you'll observe nutrient depletion as you
germinate and grow nutrient-demanding seedlings.
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This activity page will offer:
-
opportunity to germinate and grow seedlings
- experience
in determining soil nutrient levels
- operational
definition of nutrient depletion
- understanding
of the advantages of crop rotation
MATERIALS
- Corn,
sunflower or winter rye seeds*
- Two
small cups
- Nutrient
testing kit (available at local garden supply stores) Potting
soil Water
*Although almost any seed can be used, the seedlings of these
plants place high nutrient demands on the soil.
PROCEDURE
- Obtain a small bag of potting soil. Mix well so that the soil
is of uniform consistency.
- Examine the soil testing kit supplied by your instructor. What
characteristics of the soil can you test? (Accept all reasonable
answers such as pH, nitrogen, phosphorus, and potash levels)
- Select the soil nutrients that you wish to monitor. Set aside
an appropriate amount of soil to perform these tests.
- Analyze the soil and record the levels for each monitored nutrient.
- Once you know the identity of the seed you will use, research
the plant. In addition to uncovering the best way to grow seedlings,
find out how the plant is cultivated as a cash crop.
- Fill two small cups with potting soil. Follow the planting instructions
printed on the seed package. Use your finger to poke holes into
the soil. The holes should extend to the depth at which you will
bury the seeds. Add seeds to each hole. Cover will soil.
- Water and maintain the germinating seeds as suggested by your
teacher or seed packet instructions.
- After two weeks, the seedling should extend upward from the
soil surface. Select one seedling cup and remove two samples of
soil. One sample should be taken from the edge of the cup where
no rootlets can be found. The second sample should be obtained
from soil that is found within the web-like network of roots.
Test these samples for nutrient levels. Record your results.
- Maintain the second plant for an additional two weeks. After
this time, obtain two soil samples. One sample should be obtained
from an area free of roots. The other sample should be obtained
from within the matrix of rootlets. Test these samples for nutrient
levels. Record your results.
- When the activity is complete, clean your desktop. Be sure to
dispose of the soil and seedlings as directed by your instructor.
Questions
- What happened to the level of soil nutrients over time?
- What might have caused the observed change in nutrients?
- Was there a difference in the nutrient level from samples taken
from between the root system and those taken outside the root
system? Explain.
EXTENSIONS
George Washington Carver
Although
well known for his work with peanut crops, George Washington Carver
was a proponent of crop rotation. Born into slavery, Carver became
an eminent plant scientist who was interested in improving the life
of Southern farmers. He advocated alternating crops with legumes
such as peanuts which restore nitrogen to the soil. Suppose you
were interviewing George Washington Carver on a TV talk show. What
questions would you ask him about his life and research? Work with
a team of students to develop a script in which this historic figure
is interviewed by a modern day host. Students should provide the
questions and answers for the script and then act it out.
Crop Rotation
In addition to replenishing nutrients, rotating crops can help control
the population of destructive pests and diseases. Since many pests
and microbes attack only one type of plant, a yearly change of crop
offers a form of protection. Write a 2-minute radio script that
encourages owners of vegetable gardens to use crop rotation. Explain
the benefits of this strategy and how it can be used to increase
soil performance. To learn more about soils, contacts a local nursery,
gardening center, or perform an Internet search using key terms
such as "soil nutrients" and "garden fertilizers."
Local
Soil Testing
How healthy are local soils? Have an adult collect soil samples
from different locations around your school. Obtain samples from
places that include flower gardens, playing field, potted plants,
and cracks in pavement. Test these samples for nutrient levels.
Which ones have the highest load of nutrients? Which ones are poorest
in nutrients? Can you explain your findings and relate nutrient
level to physical, chemical, and biological parameters?
WEB
CONNECTION
The
Agricultural Revolution: A Four Field System
http://www.saburchill.com/history/chapters/IR/003fp.html
An essay on four-year crop rotations that were practiced during
medieval times
Tobacco
to Wheat
http://www.mountvernon.org/pioneer/farms/
tobacco_to_wheat.html
A site that surveys the plantation and agricultural strategies used
by George Washington. It includes a yearly crop rotation schedule.
Introduction
to Colonial African-American Life
http://www.history.org/Almanack/people/african/aaintro.cfm
An introduction to the colonial African American life as presented
by the Colonial Williamsburg Foundation.
The
activities in this guide were contributed by Michael DiSpezio, a
Massachusetts-based science writer and author of "Critical Thinking
Puzzles" and "Awesome Experiments in Light & Sound" (Sterling Publishing
Co., NY).
Academic Advisors for this Guide:
Corrine Lowen, Science Department, Wayland Public Schools, Wayland,
MA
Suzanne Panico, Science Teacher Mentor, Cambridge Public Schools,
Cambridge, MA
Anne E. Jones, Science Department, Wayland Middle School, Wayland,
MA
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