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Organic Matter Test
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ACTIVITY OVERVIEW
LAB O R AT
Students conduct a laboratory experiment to test the garden soil for organic matter. Students
use an experimental control as a basis of comparison. The results help determine whether the
garden soil contained sufficient nutrients. Students are then prepared to decide how to solve
the garden problem.
KEY CONCEPTS AND PROCESS SKILLS
(with correlation to NSE 5-8 Content Standards)
1.
Scientists use common units of measurement to collect data. This system is known
as the metric or international system (SI). (Inquiry: 1)
2.
Soil consists of weathered rocks and decomposed organic material from dead
plants, animals, and bacteria. (Earth Science: 1)
3.
Soils vary in composition, such as in the amount of organic matter that they contain. (Earth Science: 1)
4.
Scientists conduct experiments, make accurate measurements, and compare
results to construct scientific knowledge. (Inquiry: 1)
5.
Scientists set up controls in an experiment as a basis of comparison. (Inquiry: 1)
KEY VOCABULARY
control
milliliters (mL) organic
matter
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Activity 10 • Organic Matter Test
MATERIALS AND ADVANCE PREPARATION
For the teacher
*
2-3 large containers or tubs
transparency of Scoring Guide: GROUP INTERACTION
*
1
overhead projector
Transparency 10.1, "OM Testing Procedure" (optional)
For each group of four students
*
2
SEPUP trays
1
sample of Soil A
1
sample of Soil B
1
sample of local soil (optional)
1
cup of water
2-3 plastic tubes
2-3 tube caps
1
30-mL graduated cup
1
50-mL graduated cylinder
1
bottle of Organic Matter testing solution
(0.2 M KMnO4 [potassium permanganate] solution)
1
pipette
1
Organic Matter Color Chart
*
clock with second hand
*
piece of white paper
*
masking tape
*
paper towels
For each student
*
1
pair of safety goggles
*
1
lab apron
1
Student Sheet 2.1, "KWL: Analyzing the Garden Problem"
copy of GROUP INTERACTION Scoring Guide (optional)
*Not supplied in kit
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Organic Matter Test • Activity 10
Once again, a local soil can be added to the activity as a third soil for student investigation.
Gather large containers or tubs for soil set up and clean up. Provide them in a common area
where students can collect and return the soil easily. To clean up after the activity, decant the
permanganate solution off the top of the tub. The remaining soils can be thrown out.
Provide access to water for cleaning out the soil tubes.
Masters for Scoring Guides can be found in Teacher Resources III: Assessment.
SAFETY NOTE
Students must wear safety eyewear and a lab apron during this investigation. Do not allow
students to touch the chemicals. The OM testing solution may stain clothes and skin, so
students should rinse off any solution that touches their skin or clothes with plenty of water.
Have all students wash their hands when finished with the investigation.
The concentration of the KMnO4 solution in this activity is dilute enough that it can be safely
poured down the drain and flushed with running water.
If a more concentrated permanganate solution develops due to evaporation, it should be treated
before disposal. Either calcium (powder), calcium carbonate (crushed antacids), or
magnesium sulfate (Epsom salt) can be used to precipitate the permanganate from solution.
Dissolve one of the three substances in the potassium permanganate solution and mix until
the solution becomes clear. Then the precipitate can be thrown with solid wastes in the trash
and the liquids can be poured down the drain and flushed with running water.
TEACHING SUMMARY
Getting Started
1.
Students review the function of organic matter in a garden.
Doing the Activity
2.
(GI ASSESSMENT) Introduce the GROUP INTERACTION (GI) Scoring Guide.
3.
Students test the organic matter content of the soils.
4.
Discuss the use of a control experiment in the investigation.
Follow-Up
5.
(LITERACY) Students determine whether the school garden soil contained adequate
organic matter.
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Activity 10 • Organic Matter Test
BACKGROUND INFORMATION
Field Tests for Organic Matter
Soil organic matter (SOM) and related soil properties are probably the most widely
acknowledged indicators of soil quality. Since SOM has no definite chemical composition,
soil organic carbon (SOC) is more commonly measured and reported in scientific literature.
Soil organic carbon is naturally variable across soil types and climates. Scientists and farmers
are increasingly interested in making simple field assessments of soil quality. The USDA
Natural Resources Conservation Services has developed several tools for field tests. The test
used in this activity is based on this test.
Potassium Permanganate (KMnO4)
The OM testing solution is 0.2 M of a neutral to slightly alkaline solution. It is stable
and is appropriate to handle in concentrations of 0.0006 to 0.4 M. It is used in human and
veterinary medicine as an antiseptic treatment for skin infections and wounds. Potassium
permanganate is an oxidizing agent. In the activity, portions of the soil
organic carbon react with the KMnO 4 and bleach the solution to a light pink or clear
color. This is a result of the hydrolyzing and oxidizing effects of the KMnO4 on the
carbon compounds in the soil.
REFERENCES
Weil, R., Islam, K., Stine, M., Gruver, J., & Samson-Liebig, S. (2003). Estimating active carbon
for soil quality assessment: A simplified method for laboratory and field use. American Journal
of Alternative Agriculture, 18, 3-17.
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Activity 10 • Organic Matter Test
FOLLOW-UP
5.
too-long reaction time may create a lighter color result.
If a local soil is tested, it is not uncommon to get a clear
color result, indicating a large amount of organic matter.
Sample student results are shown in
the table below:
Sample Laboratory Results
Soil
Sample
Color After
Reaction
Result Interpretation
Soil A
magenta
some organic matter
Soil B
pink
a lot of organic matter
Control
Tube C
dark purple
no organic matter
This activity, like Activity 4, "Soil Columns,"
instructs students to measure the soil in milliliters instead
of grams, as most scientists would do. You may wish to
review why the experiment uses a measure of volume
(mL) instead of mass (g) for measuring the amount of
soil (see Teaching Suggestion 3 of Activity 4).
4.
Discuss the use of a control in the
investigation.
Use Analysis Question 1 to lead a discussion about
the use of Tube C in the experiment. Ask, Why are we
testing a tube without any soil in it? Explain that there is
no organic matter in Tube C because there is no soil in it.
Because this is known, this provides a basis of color
comparison for the other tubes, confirming that the test
worked as intended.
Review the term control. Explain that this is part of an
experiment wherein a procedure is performed with the
purpose of establishing a basis for comparison. Discuss
an example of another experiment that includes a
control. For example, if investigating Substance X to
learn whether it causes bread to rise, a good experiment
would use two loaves of bread. Both loaves would be
mixed, kneaded, and baked in an identical manner, but
one would contain Substance X and the other, the
control, would not. The control is necessary to show that
Substance X made the bread rise.
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(LITERACY) Students determine whether the
school garden soil had adequate organic
matter.
Student results should indicate that Soil B has more
organic matter than Soil A, the garden soil. Soil B
should have a lighter color than Soil A and both soil
solutions should be lighter than the control tube C.
Help students put these results in context by going back
to Student Sheet 2.1, "KWL: Analyzing the Garden
Problem," and answering the outstanding questions. An
example is shown on the next page, with the latest
additions shown in bold italics. Recall that when Ms.
Clayson brought in the other bag of soil, she mentioned
that it was from a garden where plants were growing
well.
Use Analysis Question 3 to discuss what students think
the problem is with the garden and possible solutions to
it. They will explore recommendations for the garden
further in the next activity, but start them thinking about
it by asking them to sum up their thoughts based on the
evidence presented so far. Give students an opportunity
to articulate their
individual ideas based on the evidence and group
discussion.
Write the following statements on the board and have
students complete them individually in their
science notebooks:
I think the problem with the school garden is
____________________________________________.
My evidence for this is ___________________.
Although the students have evidence that the primary
problem of the garden is a lack of nutrients, the
evidence does not give the full story. Point out that this
could result from the history of farming on the land, the
naturally sandy soil, or both. The lack of nutrients is
related to its
composition, but its cause is not exactly known.
Organic Matter Test • Activity 10
Student Sheet 2.1
"KWL: Analyzing the Garden Problem"
BEFORE the Reading
AFTER the Reading
What I know about the garden
What I want to know about the
garden
What I learned about the garden
There is a garden on the school
Why did the plants die? Could be
The school and the garden are on
property.
poor soil composition, lack of
land that was once farmland.
water, or lack of light.
There is a problem with this
The farmer once grew lettuce on
garden.
Did they get enough water? Yes.
the farm.
New plants died after they were
Does the garden get enough
Many of plants have been planted
planted.
sunlight? Yes.
in the garden and died.
The science class is going to study
Is the soil "good?" Better
The garden gets lots of sunlight
the garden.
question: Does the soil have
and is hot, with an average noon- time
enough nutrients (or organic
temperature of 21°C (70°F).
matter) for growing plants? Likely
not, since it has less than Soil B,
The soil is dry and sandy.
which is good for growing plants.
One neighbor is growing healthy
Where exactly is the school
garden? Alongside the
classrooms.
What can be planted in the
garden: flowers or vegetables?
plants in a soil of a different color.
This soil has been watered (at least
once).
Plants need water, air, sunlight,
and soil.
Possibly both.
The soil could be a problem.
What kind of plants were planted
The garden gets enough
sunlight, water, and air.
there already? Both.
Did the farming history affect the
garden? Yes, it is likely that it used
The topsoil could be missing
silt, clay, or nutrients (probably not
up a lot of the natural nutrients
missing sand).
found in the soil.
How can we test if the soil in
the garden is good for growing
The soil has less organic matter
than Soil B, which is good for
growing plants.
plants? Using an organic matter
test.
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OM Testing Procedure
Soil
Water
OM Testing
Solution
A
10 mL of Soil A
30 mL
5 mL
B
10 mL of Soil B
30 mL
5 mL
C
None
30 mL
5 mL
©2006 The Regents of the University of California
Tube
in Cup
Issues and Earth Science • Transparency 10.1
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