Teacher
Guide
CSI in the Wheat Field
Essential Question: How are soils tested?
Topical Essential Question: What variations can exist in soil samples?
Lesson Objectives:
Students will be able to:
1. Conduct pH, N, P, K soil tests.
2. Evaluate data to identify similarities in results.
3. Determine the answer to a scenario based on results.
Standards:
Middle School
MS-ESS3-4
Students who demonstrate understanding will be able to:
Construct an argument supported by evidence for how increases in human populations and
per-capita consumption of natural resources impacts Earth’s systems.
Science and Engineering Practices:
1. Asking questions
2. Developing and using models
3. Planning and carrying out investigations
4. Analyzing and interpreting data
5. Using mathematics and computational thinking
6. Constructing explanations and designing solutions
7. Engaging in argument from evidence
8. Obtaining, evaluating and communicating evidence
Crosscutting Concepts:
1. Patterns
2. Cause and Effect: Mechanisms and explanations
3. Scale, Proportion and Quantity
An education and
outreach program of:
4. Systems and System Models
5. Energy and Matter: Flows, cycles and conservation
6. Structure and Function
7. Stability and Change
Agriculture Education Benchmarks:
IAG6-5: Students will describe the role of nutrients and nutrition in plant growth.
IAG6-6: Students will discuss the importance of soil and its constituents.
Key Vocabulary:
SoilSoil testing
Organic matter
Forensic soil analysis
Materials per group:
• Suspect A, B, C or wheat field sample •
• pH tablet pack •
• Floc-Ex tablet pack •
• Nitrate tablet pack •
• Phosphorus tablet pack
• Potassium tablet pack •
• Test tube rack
•
•
Plastic spoon
One 50 mL supernatant tube
One 50 mL soil extraction tube with cap
Four square test tubes with cap (one each labeled
pH, N, P, K)
100 mL plastic beaker
pH color card
NPK color card
Materials needed but not provided:
• 60 mL Water per group
• Waste disposal bucket/trash can
• Timer (clock or watch)
NOTE TO THE TEACHER:
This lab is designed for eight groups of students where two groups are given Suspect A to test, two
groups are given Suspect B to test, two groups are given Suspect C to test, and two groups are given
the wheat field sample to test. Groups should compare their results to more accurately determine the
guilty individual.
Safety Precautions:
• Do not eat or drink in the laboratory.
• Wear safety glasses, lab coat and gloves when performing the experiment.
An education and
outreach program of:
Total Duration:
15-20 min. pre-lab prep time; 40-50 min. class time
Lab Background Information:
NOTE: This is background information for the
teacher to assist in facilitating learning and will
be explained to the students after the Explore
section.
“Soil is made of life. Soil makes life. And soil is
life.” (David Lindbo and others, 2008)
Soil is one of Earth’s most valuable resources. It is
the outermost layer of the Earth’s surface and is
capable of supporting plant growth and ultimately life on Earth. We rely on plants to supply the food we eat, the clothes we wear, the shelter we live
in and the oxygen we breathe. Without plants, there would be no life; without soil, there would be no
plants.
What is soil? Soil is not dirt! Dirt is what we get
under our fingernails. It is something we want to
wash off and get rid of. Soil is a complex mixture
of minerals, air, water and organic matter (dead
and decaying plant and animal matter).
There is chemistry in soil!
All nutrients in our food originate from the soil.
Plants require and take up nutrients from the
soil, and we eat the plants or animals that ate the
plants. Optimum plant health depends on the soil
having an adequate supply of plant nutrients.
There are 14 essential elements in the soil that are
classified as plant nutrients. Of these, nitrogen
(N), phosphorus (P) and potassium (K) are used
in the largest quantities by the plants and are considered the primary soil nutrients.
Soil pH is a measurement of the acidity or alkalinity of a soil. On the pH scale, a pH of 7.0 is neutral, below 7.0 is acidic and above 7.0 is basic, or alkaline. Soil pH is an important chemical property because it
affects the availability of nutrients to plants and the activity of soil microorganisms.
Soil testing is a management tool used to determine pH and nutrient concentrations within a soil sam-
An education and
outreach program of:
ple. Soils vary widely in their composition depending on the material from which they form (parent material); forces involved in their development such as wind, water and ice; microbe content; and the time
it took to form them. It isn’t uncommon for a soil sample to vary from meter to meter within a field. Soil
testing enables producers to maintain proper chemical and microbiological balance within a soil, which
optimizes crop production without depleting nutrient reserves.
Forensic soil analysis is the use of soil sciences and other disciplines to aid in criminal
investigation. Soils are like fingerprints because every type of soil that exists has unique
properties that act as identification markers. This means that the origin of the soil
sample can be identified. For example, soil embedded in the shoe of a criminal can be
matched to a specific soil type found along a lake where a murder victim was discovered, based on soil type and microbial and insect content specific to certain areas.
Engage:
To discuss the importance of soil, demonstrate the concept of how little soil is available
on our planet using the apple analogy:
• Take a whole apple and cut away one-fourth; 75 percent of Earth’s surface is water
and 25 percent is dry land.
• Cut that one-fourth of the apple in half. Of that 25 percent of dry land, half of it is
desert, polar or mountainous and can’t be used. This leaves 12.5 percent of Earth.
• Cut that one-eighth slice in half. Of this 12.5 percent of dry land that is left, 50 percent is limited by terrain, fertility or excessive rainfall and cannot support food production.
• From that one-sixteenth of the apple, cut away the skin from the flesh. Of the
one-sixteenth of the planet left that is available for food production, we also have to
have homes, offices, hospitals, roads and more. What is left for food production is
very small, only about 3 percent of Earth’s surface.
• Discuss that the soil that is left is threatened by erosion and contamination. Additionally, as the
population grows, it will require more space, which threatens the amount of soil available for growing food as well as increases soil contamination. As a result, agriculturalists are very concerned with
preserving the soil, using it wisely and improving the nutrients available for plants.
Introduction
In this activity, you will learn about the importance of soil chemistry; how to test a soil sample for the
nitrogen, phosphorus and potassium; and how to determine the pH of a soil sample.
Explore:
Scenario
A crime has been committed in a local wheat field, and area law enforcement officers have detained
three suspects (suspects A, B and C) that may have committed the crime. Soil samples have been col-
An education and
outreach program of:
lected from the suspects’ shoes and have been sent to you for analysis. Your job is to perform four soil
tests on one of the shoe samples or on a sample from the wheat field. Once the tests are concluded,
you’ll need to share your data with other groups to gather evidence to determine which suspect, if any,
was in the wheat field where the crime was committed.
Procedure:
Activity 1: Soil Extraction
1. Fill the round soil extraction tube to the 30 mL line with water.
2. Add two Floc-Ex tablets to the tube. Cap the tube.
3. Mix by shaking the tube for 30 seconds. Then set the tube on a stable surface.
4. Remove the cap from the pH test tube, then use the plastic spoon to fill the cap full with soil from
the soil sample bag. Then empty the cap of soil into the soil extraction tube.
5. Cap the tube and shake for one minute.
6. Let the tube stand until the soil settles. While waiting for the soil to settle, conduct the pH test and
then come back to Step 7 below.
7. Use a pipette to transfer the clear solution above the soil in the soil extraction tube to the 50 mL
supernatant tube. Be sure to have at least 25 mL.
8. Continue to Activity 3: Testing for Nitrogen.
Activity 2: Testing for pH
1. Fill the pH test tube with 10 mL of water.
2. Add one soil pH tablet from the package.
3. Fill the cap of the pH test tube with soil from your soil sample bag and add it to the pH test tube.
4. Cap the tube and mix the contents by inverting the test tube 10 times. Be sure that there is no soil
left on the bottom of the test tube when it is held upside down.
5. Replace the tube in the test tube rack.
6. Return to Step 7 of Activity 1.
Activity 3: Testing for Nitrogen
1. Using a pipette, transfer 10 mL of the supernatant to the square test tube labeled “Nitrogen (N).”
2. Add one nitrate tablet to the tube. If you are working outside, immediately slide the tube into the
protective sleeve and don’t remove for at least five minutes.
3. Place the cap on the tube and mix by inverting for two minutes to disintegrate the tablet. It is OK
if bits of material remain in the sample.
4. Place tube in the test tube rack and allow the sample to rest for five minutes so the color can
develop.
An education and
outreach program of:
Activity 4: Testing for Phosphorus
1. Using a pipette, transfer 10 drops of the supernatant to the test tube labeled “Phosphorus (P).”
2. Raise the volume of the solution in the test tube to 10 mL by adding water.
3. Add one phosphorus tablet to the test tube. Then place the cap on the tube and invert tube until
the tablet dissolves.
4. Place in the test tube rack to allow the tube to develop for five minutes.
Activity 5: Testing for Potassium
1. Using a pipette, transfer 10 mL of the supernatant to the square test tube labeled
“Potassium (K)”.
2. Add one potassium tablet to the test tube.
3. Cap the tube and invert until the tablet disintegrates.
4. Place tube in the test tube rack and let develop for five minutes.
Collecting Data
It is best to allow the samples to have at least five minutes of rest in order for the reactions to occur.
Once the samples have had sufficient time to react, it is time to record the results.
pH Test:
1. Hold the test tube against the white part of the pH color chart and match the color of the liquid
to the color on the chart it most closely matches.
2. Record your results as pH in your data table.
Nitrogen Test:
1. Hold the test tube against the white part of the NPK color card next to the nitrogen squares.
Compare the color of the solution to the nitrogen squares and select the color that best matches
your test tube. (If your sample was in the sleeve, remove it to evaluate color.)
2. Record your results as low, medium or high in your data table.
Phosphorus Test:
1. Hold the test tube against the white part of the NPK color card next to the blue squares for phosphorus. Compare the color of the solution to the phosphorus squares and choose the color that
best matches your test tube.
2. Record your results as low, medium or high in your data table.
Potassium Test:
1. Compare the cloudiness of the solution in your test tube to the potassium section on the NPK
color chart. To do this, hold the tube over the black boxes in the left column and look through
An education and
outreach program of:
your test tube to compare the color through the liquid to the shaded boxes in the right column.
2. Record your results as low, medium or high in your data table.
Gathering Evidence
1. After you have completed gathering data on your suspect, talk to the scientists from other
groups to obtain data to complete your Soil Test Data Table.
2. Identify the suspect that you believe was in the wheat field by circling their letter in your chart.
CSI in the Wheat Field: Soil Test Data Table
Soil Test
Sample Tested
Nitrogen
Phosphorus
Potassium
pH
A
Low
High
Low
Vary
B
High
Low
High
Vary
C
Low
Low/Medium
Low
Vary
Wheat Field
High
Low
High
Vary
NOTE TO THE TEACHER:
When cleaning up after the lab, have students dispose of the test tube contents in a bucket or pail. This
way the soil doesn’t end up down the drain and cause plumbing problems. Once the soil has settled in
the disposal bucket, the supernatant (remaining fluid) can be removed and disposed of in the sink with
copious amounts of water. In the exploration trunk, wash bottles are provided to aid in removing the
soil from the test tubes.
Explain: (see lab background)
The Lab Background Information from the Teacher Guide is repeated in the Explain section of the Student Guide. Below is additional information to help aid explanations.
You can easily extend this lesson to discuss fertilizers with the students. It is important to recognize
that after conducting the soil test, if the nutrients are low or the pH is too high or low, then soil amendments need to be added to allow the plants to grow to their full potential. There are a wide variety of
fertilizers on the market today for both the backyard gardener and the production farmer that come in
An education and
outreach program of:
different forms and are made from different products. Most fertilizers contain the three major macronutrients – nitrogen, phosphorus and potassium. These are called complete fertilizers. Other fertilizers
only include one or two of the major macronutrients and are called incomplete fertilizers.
If the soil pH needs to be adjusted, there are soil amendments that can be added. If the soil is too
acidic and pH needs to be raised, crushed limestone can be incorporated into the soil. The lime, which
is calcium carbonate (CaCO3), reacts with the water in the soil to take hydrogen ions from the soil and
form water and carbon dioxide. This process raises the pH of the soil by removing excess hydrogen
ions from the soil.
If a soil is too alkaline, the fastest way to lower the pH to a more neutral range is to add elemental sulfur
to the soil. Bacteria in the soil combined with soil water break down the sulfur to form sulfuric acid
(H2SO4). In this case, the sulfur is oxidized, reducing the amount of hydroxide ions in the soil, making it
more acidic.
2S + 2H2O + 3O2 = 2H2SO4
Elaborate:
Optional Extension Activities
Soil test kits can be purchased at your local farm/tractor supply or home improvement store and are
relatively inexpensive. They can also be purchased online from the following sites:
N•P•K: http://www.carolina.com/environmental-science-soil-studies/lamotte-n-p-k-soil-test-kit/181875.
pr?catId=&mCat=&sCat=&ssCat=&question=soil+test+kit
pH: http://www.carolina.com/environmental-science-soil-studies/lamotte-soil-ph-testab-kit/181876.
pr?catId=&mCat=&sCat=&ssCat=&question=soil+test+kit
Use the kits to try testing the soil in your gardens or flower beds at home to determine if your plants
are growing in optimum soil conditions.
You may also try fertilizing the plants growing around your home. Test the soil prior to fertilization
(baseline) and after fertilization to determine how the fertilizer changed the chemistry of the soil. How
long does it take for the soil to return to the baseline? Has it rained lately? How would this affect the
soil chemistry after fertilization?
An education and
outreach program of:
Evaluate:
1. What factors affect the composition of soil?
Parent material, forces causing its formation (wind, water, ice), microbial content of soil, and the
time it took to form
2. Of the 14 essential elements needed by plants, which are needed in the highest quantity?
Nitrogen, phosphorus, potassium
3. How does pH affect plant growth?
pH affects the availability of nutrients to plants which can improve or retard growth of the plants.
Microbes in the soil can have a beneficial effect on plants, and pH levels will affect their ability to
survive.
4. Why is soil testing an important tool for agriculturalists and gardeners to use?
Soils in the same field or garden can vary in nutrient content. As plants need certain nutrients for
proper growth, a producer needs to know what nutrients and how much to apply to their field in
order to maximize the growth of their crops.
5. Based on your test results, which suspect was most likely the guilty of the crime? Justify your answer using your data.
Data should lead students to conclude that Suspect B is the most likely suspect as it matches
most closely with the wheat field sample (pH – 7; N – high; P – medium; K – high).
6. A shovel covered in dried dirt and plant material has been discovered at the home of a murder suspect. What characteristics about the possible burial site could scientists discover from this piece of
evidence that would allow them to narrow down the search area?
Soil type, parent material (specific types of rocks and minerals), pH level, nutrient content, specific insect and microbe types, the species of plants. All of these could be used to narrow down
the possible burial sites. Specific types of plants, insects and microbes are unique to geographic
regions; scientists could narrow down locations in that region based on soil type and mineral
content.
Noble Academy would like to thank the following people for their contributions to this lesson:
• Quentin Biddy
• Susie Edens
• Kay Gamble
• Janie Herriott
• Fiona McAlister
• Julie Smiley-Foster
An education and
outreach program of:
Student
Guide
CSI in the Wheat Field
Essential Question: How are soils tested?
Topical Essential Question: What variations can exist in soil samples?
Lesson Objectives:
Students will be able to:
1. Conduct pH, N, P, K soil tests.
2. Evaluate data to identify similarities in results.
3. Determine the answer to a scenario based on results.
Key Vocabulary:
SoilSoil testing
Organic matter
Forensic soil analysis
Materials per group:
• Suspect A, B, C or wheat field sample •
• pH tablet pack •
• Floc-Ex tablet pack •
• Nitrate tablet pack •
• Phosphorus tablet pack
• Potassium tablet pack •
• Test tube rack
•
•
Plastic spoon
One 50 mL supernatant tube
One 50 mL soil extraction tube with cap
Four square test tubes with cap (one each labeled
pH, N, P, K)
100 mL plastic beaker
pH color card
NPK color card
Safety Precautions:
• Do not eat or drink in the laboratory.
• Wear safety glasses, lab coat and gloves when performing the experiment.
Engage:
How much soil exists on this planet for us to use for food production? Watch the demonstration to find
out!
An education and
outreach program of:
Introduction:
In this activity, you will learn about the importance of soil chemistry; how to test a soil sample for the
nitrogen, phosphorus and potassium content; and how to determine the pH of a soil sample.
Explore:
Scenario
A crime has been committed in a local wheat field, and area law enforcement officers have detained
three suspects (suspects A, B and C) that may have committed the crime. Soil samples have been collected from the suspects’ shoes and have been sent to you for analysis. Your job is to perform four soil
tests on one of the shoe samples or on a sample from the wheat field. Once the tests are concluded,
you’ll need to share your data with other groups to gather evidence to determine which suspect, if any,
was in the wheat field where the crime was committed.
Procedure:
Activity 1: Soil Extraction
1. Fill the round soil extraction tube to the 30 mL line with water.
2. Add two Floc-Ex tablets to the tube. Cap the tube.
3. Mix by shaking the tube for 30 seconds. Then set the tube on a stable surface.
4. Remove the cap from the pH test tube, then use the plastic spoon to fill the cap full with soil from
the soil sample bag. Then empty the cap of soil into the soil extraction tube.
5. Cap the tube and shake for one minute.
6. Let the tube stand until the soil settles. While waiting for the soil to settle, conduct the pH test and
then come back to Step 7 below.
7. Use a pipette to transfer the clear solution above the soil in the soil extraction tube to the 50 mL
supernatant tube. Be sure to have at least 25 mL.
8. Continue to Activity 3: Testing for Nitrogen.
Activity 2: Testing for pH
1. Fill the pH test tube with 10 mL of water.
2. Add one soil pH tablet from the package.
3. Fill the cap of the pH test tube with soil from your soil sample bag and add it to the pH test tube.
4. Cap the tube and mix the contents by inverting the test tube 10 times. Be sure that there is no soil
left on the bottom of the test tube when it is held upside down.
5. Replace the tube in the test tube rack.
6. Return to Step 7 of Activity 1.
An education and
outreach program of:
Activity 3: Testing for Nitrogen
1. Using a pipette, transfer 10 mL of the supernatant to the square test tube labeled “Nitrogen (N).”
2. Add one nitrate tablet to the tube. If you are working outside, immediately slide the tube into the
protective sleeve and don’t remove for at least five minutes.
3. Place the cap on the tube and mix by inverting for two minutes to disintegrate the tablet. It is OK
if bits of material remain in the sample.
4. Place tube in the test tube rack and allow the sample to rest for five minutes so the color can
develop.
Activity 4: Testing for Phosphorus
1. Using a pipette, transfer 10 drops of the supernatant to the test tube labeled “Phosphorus (P).”
2. Raise the volume of the solution in the test tube to 10 mL by adding water.
3. Add one phosphorus tablet to the test tube. Then place the cap on the tube and invert tube until
the tablet dissolves.
4. Place in the test tube rack to allow the tube to develop for five minutes.
Activity 5: Testing for Potassium
1. Using a pipette, transfer 10 mL of the supernatant to the square test tube labeled
“Potassium (K)”.
2. Add one potassium tablet to the test tube.
3. Cap the tube and invert until the tablet disintegrates.
4. Place tube in the test tube rack and let develop for five minutes.
Collecting Data
It is best to allow the samples to have at least five minutes of rest in order for the reactions to occur.
Once the samples have had sufficient time to react, it is time to record the results.
pH Test:
1. Hold the test tube against the white part of the pH color chart and match the color of the liquid
to the color on the chart it most closely matches.
2. Record your results as pH in your data table.
Nitrogen Test:
1. Hold the test tube against the white part of the NPK color card next to the nitrogen squares.
Compare the color of the solution to the nitrogen squares and select the color that best matches
your test tube. (If your sample was in the sleeve, remove it to evaluate color.)
2. Record your results as low, medium or high in your data table.
An education and
outreach program of:
Phosphorus Test:
1. Hold the test tube against the white part of the NPK color card next to the blue squares for phosphorus. Compare the color of the solution to the phosphorus squares and choose the color that
best matches your test tube.
2. Record your results as low, medium or high in your data table.
Potassium Test:
1. Compare the cloudiness of the solution in your test tube to the potassium section on the NPK
color chart. To do this, hold the tube over the black boxes in the left column and look through
your test tube to compare the color through the liquid to the shaded boxes in the right column.
2. Record your results as low, medium or high in your data table.
Gathering Evidence
1. After you have completed gathering data on your suspect, talk to the scientists from other
groups to obtain data to complete your Soil Test Data Table.
2. Identify the suspect that you believe was in the wheat field by circling their letter in your chart.
CSI in the Wheat Field: Soil Test Data Table
Soil Test
Sample Tested
Nitrogen
Phosphorus
Potassium
pH
A
B
C
Wheat Field
Explain:
“Soil is made of life. Soil makes life. And soil is life.” (David Lindbo and others, 2008)
Soil is one of Earth’s most valuable resources. It is the outermost layer of the Earth’s surface and is capable of supporting plant growth and ultimately life on Earth. We rely on plants to supply the food we
eat, the clothes we wear, the shelter we live in and the oxygen we breathe. Without plants, there would
be no life; without soil, there would be no plants.
An education and
outreach program of:
What is soil? Soil is not dirt! Dirt is what we get
under our fingernails. It is something we want to
wash off and get rid of. Soil is a complex mixture
of minerals, air, water and organic matter (dead
and decaying plant and animal matter).
There is chemistry in soil!
All nutrients in our food originate from the soil.
Plants require and take up nutrients from the
soil, and we eat the plants or animals that ate
the plants. Optimum plant health depends on
the soil having an adequate supply of plant nutrients.
There are 14 essential elements in the soil that are classified as plant nutrients. Of these, nitrogen (N),
phosphorus (P) and potassium (K) are used in the largest quantities by the plants and are considered
the primary soil nutrients.
Soil pH is a measurement of the acidity or alkalinity of a soil. On the pH scale, a pH of 7.0 is neutral, below 7.0 is acidic and above 7.0 is basic, or alkaline. Soil pH is an important chemical property because it
affects the availability of nutrients to plants and
the activity of soil microorganisms.
Soil testing is a management tool used to determine pH and nutrient concentrations within
a soil sample. Soils vary widely in their composition depending on the material from which
they form (parent material); forces involved
in their development such as wind, water and
ice; microbe content; and the time it took to
form them. It isn’t uncommon for a soil sample
to vary from meter to meter within a field. Soil
testing enables producers to maintain proper
chemical and microbiological balance within a
soil, which optimizes crop production without
depleting nutrient reserves.
Forensic soil analysis is the use of soil sciences and other disciplines to aid in criminal investigation.
Soils are like fingerprints because every type of soil that exists has unique properties that act as identification markers. This means that the origin of the soil sample can be identified. For example, soil
embedded in the shoe of a criminal can be matched to a specific soil type found along a lake where a
murder victim was discovered, based on soil type and microbial and insect content specific to certain
areas.
An education and
outreach program of:
Elaborate:
Soil test kits can be purchased at your local farm/tractor supply or home improvement store and are relatively inexpensive. They can also be purchased online from the following sites:
N•P•K: http://www.carolina.com/environmental-science-soil-studies/lamotte-n-p-k-soil-test-kit/181875.
pr?catId=&mCat=&sCat=&ssCat=&question=soil+test+kit
pH: http://www.carolina.com/environmental-science-soil-studies/lamotte-soil-ph-testab-kit/181876. pr?catId=&mCat=&sCat=&ssCat=&question=soil+test+kit
Use the kits to try testing the soil in your gardens or flower beds at home to determine if your plants are
growing in optimum soil conditions.
You may also try fertilizing the plants growing around your home. Test the soil prior to fertilization (baseline) and after fertilization to determine how the fertilizer changed the chemistry of the soil. How long does
it take for the soil to return to the baseline? Has it rained lately? How would this affect the soil chemistry
after fertilization?
Evaluate:
Name: ______________________________________________
Use knowledge gained from this lesson to complete the questions.
1. What factors affect the composition of soil?
2. Of the 14 essential elements needed by plants, which are needed in the highest quantity?
3. How does pH affect plant growth?
An education and
outreach program of:
4. Why is soil testing an important tool for agriculturalists and gardeners to use?
5. Based on your test results, which suspect was most likely the guilty of the crime? Justify your answer
using your data.
6. A shovel covered in dried dirt and plant material has been discovered at the home of a murder suspect.
What characteristics about the possible burial site could scientists discover from this piece of evidence
that would allow them to narrow down the search area?
An education and
outreach program of: