3. Soil Analysis

Soil Profile from Tabott county, Tennessee

Summary
Students conduct 4 tests of soil quality in the classroom that can then be applied to their terraqua columns and to the outdoors: visual observation, soil separation, pH, and Tullgren Funnel (to isolate living things in the soil). They make comparisons between 2 different types of soil and draw conclusions about how "healthy" each soil is. Through this process, students discover the major "ingredients" of soil: clay, silt, sand, organic material, water, air, living things, and minerals. By recording information in their science journals, they learn how to keep good notes and share the information with others in the class during a concluding class discussion about what "healthy" soil might look like and why.

Objectives
Can describe the major components of soil.
Can make comparisons between different soils.
Can conduct tests of soil quality.
Can interpret tests of soil quality.
Can record data in a science lab notebook.

Vocabulary
loam
clay
silt
sand
organic material
Tullgren Funnel
pH
acid
base

AttachmentSize
3soil_analysis.doc58 KB
soil_homework.doc27.5 KB
soil_questions.doc28 KB
soil_stations.doc39 KB

3. Soil Analysis - Logistics

Time

Day 1: Optional: 5 min discuss soil observation homework from last night 10 min observe samples of different soil ingredients 30-40 min conduct soil quality tests

Day 2 (several days later): 15 min complete observations of Tullgren Funnel and soil separation tests 30 min discuss results and draw conclusions about "healthy" versus "unhealthy" soil

* Since the Tullgren Funnel and soil separation tests take several days, it is recommended to start Day 1 on a Friday and complete Day 2 on a Monday. *

Grouping
2-3 students

Materials
For each group of students:

  • 4 petri dishes
  • 2 funnels (card stock paper rolled and taped into a funnel shape and cut to 4-6 inches tall may be substituted)
  • 2 funnel holders to hold funnels upright above a Petri dish (card stock paper rolled into a tube works well or you can eliminate the Petri dish as well by using a cup that the body of the funnel rests in as long as the bottom tip of the funnel does not touch the bottom of the cup)
  • 2 square of cheesecloth
  • 2 strips pH paper
  • 2 white paper towels
  • 2 clear 15 ml tubes with lids, glass or plastic

For whole class to share:

  • Clay in ziplock bag
  • Sand in ziplock bag
  • Silt in ziplock bag
  • Compost in ziplock bag
  • 8 large plastic cups
  • 8 plastic spoons
  • 2 graduated cylinders
  • 2 tablespoons
  • 2 rulers
  • 2 different types of soil (The more different the texture, composition, and organism content of the 2 soils, the better. For example, try soil from the school yard vs. store-bought potting soil, a clay soil vs. a sandy soil, or rich garden soil vs. soil from an abandoned lot.)
  • 3-4 bare light blubs hung or mounted approximately 1 foot from the table top (desk lamps work well)
  • 1 small jar alum (available at supermarkets for pickling)
  • 2 magnifying glasses
  • 1 package removable dot labels or rolls of masking tape

Setting
classroom

3. Soil Analysis - Background

Teacher Background
In an ecosystem, the soil and water form the foundation of the surrounding environment. Environmental impacts such as deforestation, the introduction of invasive species, climate change, acid rain and others all have profound implications on the soil and water in the area. Many changes can be readily detected and tracked by very simple tests that students can conduct with very simple materials. This lesson and the parallel water quality analysis lesson are opportunities to teach students the observational and analytical skills needed to apply these tests to real ecosystems in the real world.

The first test is a simple soil observation using all your senses. This allows students to practice observation and recording skills and helps kids notice that all soil is not the same.

The second test is a soil separation test to determine the relative proportion of clay, silt, sand and organic material. It draws on the principle of a density column where the largest, most dense particles (in this case sand) settle first. During the introduction of this portion of the activity, you can discuss density or not, depending on the background of your students. Students generally intuitively understand that in water, big heavy things will sink first. Clay soils tend to be sticky when wet and will hold together in a ball. When dry, clay soils harden to an almost rock-like density, holding very little air, thus making it difficult for critters to survive. Sandy soils tend to drain water rapidly. From a gardener's perspective, the ideal soil is a balanced mixture of sand, silt and clay with lots of air, water and organic material mixed in. The alum used during this test helps separate the particles of soil. Alum is relatively non-toxic but students should be warned not to put it in their mouths and should wash their hands after this station (and at the end of the period).

The third test measures the pH of the soil. pH is a measure of the chemical and mineral content of soil. Most plants prefer soil that is slightly acidic (between 5.5-7). However, some plants require very acidic soils (less than 4.5) to survive (such as blueberries and azaleas). Impurities and pollutants such as detergents, acid rain, and trash will alter the pH of soil. Major human disruption from mining, logging, and construction also changes the pH of soil by allowing the more neutral topsoil to erode, exposing the subsoil layers which tend to be more acidic.

The final test uses a Tullgren funnel (sometimes called a Berlese separator) to isolate bugs, worms and other critters from the soil. The basic principle is that the soil is placed in a funnel beneath a heat source. The mites, worms, and insects in the soil move downward through the soil to escape the heat and eventually fall out the bottom of the funnel into water. It can be absolutely fascinating for students to discover that soil is alive with critters large and small. Because it takes some time for the critters to fall through the funnel, (between 2-4 days) it is often ideal to allow the test to continue over a weekend. But make sure that there is enough water is the Petri dishes or the cup so that the water below the funnel does not dry out. For additional information and ideas about the Tullgren Funnel, see: The Open Door Website. How do you identify the critters? Great question and as of now, I have no idea. I have not found a good field guide which can be used to identify soil critters. If you find something, let us know!

Additional tests may be used or substituted for the 4 included here. For instance, you can measure the water-holding capacity of soil by adding fixed quantities of water (10 mls at a time for instance) to fixed quantities of dry soil in a funnel until water begins to drain out of the bottom. Water will continue to drain out the bottom until the soil reaches a steady state. Take the amount of water you added initially and subtract the amount of water that drained out and you have your water-holding capacity. This measurement relates closely to the composition of the soil. The more clay, the more water the soil holds. The more sand and gravel, the less water the soil holds.

What makes up healthy soil? In general, a balance of all soil ingredients with few pollutants and lots of organic material and living things makes healthy soil. Soil that completely lacks organic material or that is far outside the normal pH range is generally considered unhealthy. Soil that is completely dry cannot support life. A large number of soil critters is often a good indicator of healthy soil. However, this depends dramatically on the location and use of the soil. Soil in a garden will be different from forest soil which will be different from creek soil. Therefore, in the discussion of what makes healthy soil, expect and encourage differences in opinion.

Student Prerequisites
It is recommended that students are familiar with pH - both understanding what pH is a measure of relative to household items and how to measure it using indicators. The previous lesson 2. Water Analysis provides a sufficient introduction to those ideas.

Optional: Comparing Soil Homework - This assignment asks students to observe and compare 2 samples of soil, one from home, one from school, and to devise original tests to look for differences between the soils.

3. Soil Analysis - Getting Ready

Getting Ready

  1. Prepare 4 stations around the classroom with the materials needed to conduct that test and a printout of the instructions (attachments can be found on the bottom of the summary page).
    1. Soil observation: paper towels, magnifying glass, 2 different soils labeled in plastic cups, spoons
    2. pH: petri dishes, pH paper, labels, graduated cylinders, 2 different soils labeled in plastic cups, tablespoons
    3. Soil separation: 15 ml tubes, alum, ruler, labels, 2 different soils labeled in plastic cups, spoons
    4. Tullgren Funnel: lightbulbs, funnels, cheesecloth squares, funnel holder, petridishes or cups, labels, 2 different soils labeled in plastic cups, spoons
  2. Set up an example of a Soil separation test and a Tullgren funnel test at each of those stations.

3. Soil Analysis - Lesson Plan

Lesson Plan

  1. Discuss the Comparing Soil Homework from the night before. This assignment asks students to observe and compare 2 samples of soil, one from home, one from school, and to devise original tests to look for differences between the soils. Some examples of questions to ask:
    • What did you observe about the school soil? about your home soil?
    • What was similar? What was different?
    • What ingredients make up soil?
    • What test did you try?
    • What did you discover?
    • What other tests could we use?
  2. Show and pass around the ziplock bags of clay, silt and sand. Allow students to make comparisons between the different materials and lead them to the conclusion that clay, silt and sand are all made of rock that has been ground down to different sizes, clay being the smallest, sand being the largest. Begin a list of soil "ingredients" on the board.
  3. Pass around the ziplock bag of compost. Discuss what compost is (dead, decaying organic material) and where it comes from. Discuss whether compost is good or bad for soil and consider the reasons why.
  4. Ask the students what other ingredients are in soil and complete the list on the board. The major other components include water, air, living things, and minerals.
  5. Optional: Discuss whether all soils have all ingredients and what the effect of missing ingredients might be.
  6. Introduce today's lab and offer a brief explanation of the 4 stations students will rotate through. Ask the question why are we comparing soils and what would we want to discover?
  7. Specify the organization of the student's lab notebook and decide how data should be recorded at each station.
  8. Divide the students into groups and specify the rotation strategy. Rotate through the 4 stations, giving students 5-10 minutes per station. Allow time for a thorough clean up at the end of each station.
  9. 2-4 days later, give students 5-10 minutes to check back on their soil separation and Tullgren Funnel tests and record their results.
  10. Engage the students in a discussion of the differences between the 2 soils. One way to do this would be to create a table at the front of the classroom with columns for each of the 2 soils and rows for each of the 4 tests. Students can offer observations and comparisons for each test to add to the summarized results at the front of the room. Some examples of questions to ask:
    • Were you surprised by any of the results?
    • What do differences in pH mean?
    • What might cause pH differences?
    • How should we interpret differences in the relative amounts of clay, silt and sand?
    • Was any layer missing?
    • How would differences in soil composition affect the types of plants or animals that could live in that soil?
    • Does knowing where the 2 soils came from help explain any of the results?
    • Did everyone get the same results? Why or why not?
  11. Armed with a thorough analysis of these 2 soils, begin a discussion of what makes soil "healthy". Challenge students to decide which of the 2 soils is "healthiest". This question is very open-ended and does not have a right or wrong answer but is an excellent way to generate discussion and delve deeply into the issue of soil quality. One way to conduct this discussion is to allow students time to speak with their group about the question first, then share the group's conclusion with the rest of the class. A key factor to bring up is whether "healthy" soil is the same regardless of its location or use (such as a garden, schoolyard, desert, forest or creek).

3. Soil Analysis - Assessments

Assessment

  1. Soil Analysis homework (downloadable below). In this assignment, students review the soil analysis test, the major ingredients in soil, and think about why soil is important to an ecosystem.
  2. Describe one thing that humans do that changes the health of the soil - either making it worse or better. How would it affect each of the 4 tests we conducted during class?

Going Further

  1. Conduct soil analysis on the planter part of the terraqua column. See Terraqua Column lesson.
  2. Conduct soil analysis at the creek restoration site before and after restoration. A structured way of conducting this lesson is available as part of the Habitat Survey lesson later in this unit.
  3. Conduct an independent investigation using terraqua columns that monitors soil quality. See Terraqua Column Experiment project.
  4. Continue the study of sediments, first through studying erosion patterns in a classroom model (see the Erosion Patterns lesson) and then through the study of sediments collected from different sites along a local creek (see Sediment Study Project).

AttachmentSize
Soil analysis questions.doc28 KB

3. Soil Analysis - Sources and Standards

Sources
Terrarium Habitats a GEMS guide by the Lawrence Hall of Science includes a great soil observation activity, including the soil separation test and Tullgren Funnel test.

The Open Door Website describes the Tullgren Funnel test with pictures and additional details.

Standards
Grade 6
Shaping Earth's Surface
2. Topography is reshaped by the weathering of rock and soil and by the transportation
and deposition of sediment.

Ecology (Life Sciences)
5. Organisms in ecosystems exchange energy and nutrients among themselves and with the environment. As a basis for understanding this concept:
e. Students know the number and types of organisms an ecosystem can support depends on the resources available and on abiotic factors, such as quantities of light and water, a range of temperatures, and soil composition.

Grade 8
Reactions
5. Chemical reactions are processes in which atoms are rearranged into different combinations of molecules. As a basis for understanding this concept:
e. Students know how to determine whether a solution is acidic, basic, or neutral.

All grades
Investigation and Experimentation
7. Scientific progress is made by asking meaningful questions and conducting careful investigations. As a basis for understanding this concept and addressing the content in the other three strands, students should develop their own questions and perform investigations.