Unit 3: Soil Investigation and Classification

• Record and interpret data they collect from class soil samples
• Discuss how soil characteristics and formation may help us to address the grand challenges facing society
• Discuss how data informs interdisciplinary soils issues working across multiple Earth systems

Unit 3 is designed for elementary education pre-service teachers (students) in an undergraduate or graduate level science teaching methods course. It could be easily modified for non-teaching students by altering questions that refer to teachers, future classrooms/students, or standards. It is designed for a lab or block type course where the instructor has 2.5–3 hours at one time. The activity consists of discussion sessions prior to and following student activities at the soil testing inquiry stations. This unit is the third of four units within the Soils, Systems, and Society module. Although the activities described here can stand alone, the other units are referred to and provide more context.

Instructor Preparation Prior to Class

• Collect at least three types of soil and parent rock material from the field. Bake and prepare the soil as described in the attached Soil Collection Protocol (Microsoft Word 2007 (.docx) 18kB Jan13 16). In addition, if Soil Station 7, Soil Erosion, is going to be included, then soil with cryptogams must be included - see Teaching Notes below.
• Use the resources listed below to help familiarize yourself with your local soils prior to soil collection.
• When collecting, record the GPS coordinates of soil sampling locations in latitude and longitude (degrees, minutes, seconds, degrees and decimal minutes, or decimal degrees), using Google Maps or a GPS.
• Use Google Maps or another resource to plot the location of the soils you collected on a map. Or, if time allows, students can plot GPS coordinates in class. The simplest way to plot the soil sample locations is Google Maps; see instructions below.
• Arrange materials for each of the eight stations in the classroom. Print the Soil Activity Cards (Microsoft Word 2007 (.docx) 118kB Jan7 16) for each station for students to read and follow as they work.

Soil Sample Locations Inquiry (30 min) (This may be done prior to the class period in which students collect data at the soil stations.)

Show the class the soil samples plotted on Google Maps. Tell the students that we will be analyzing the properties of these soils today or in the near future. Then you can ask them the following questions for discussion:

• Look at the location of the soil samples in the landscape. What patterns do you observe? Write down several observations in your science notebook.
• What landscape features (e.g., rivers, lakes, hillsides, mountains, floodplains, etc.) do you observe on the map? What soils do you find near each feature?
• What is the vegetation composition (e.g., dense forest, agricultural fields, grass, no vegetation) near each soil sample?
• Discuss with your group or with the entire class the origin of the soils you have mapped and the possible transportation processes they would have had to go through.
  

This is also a good time to discuss why we collect and record this kind of data: it allows us to characterize the soil and to consider the different soils' possible uses in society.

Station Introduction (30 min)

Have students revisit their testable questions from their Soils and Society Issues Homework Assignment (Microsoft Word 2007 (.docx) 21kB Jan6 16) completed for Unit 1. Stations are set up around the room, and students break into small groups to explore the soil investigation and classification method stations that could apply to their Kits. The instructor assists groups as necessary.

The instructor should briefly introduce them to each station (using information in the descriptions) and point out any safety issues or difficult methods. Use questioning to invite student participation during the introduction. From their homework, students should be able to determine which stations apply to their Kits. The instructor should also explain the logistics of visiting the stations. With a small class it may be appropriate to let each candidate work through the stations at his or her own pace.

Students should record, analyze, and interpret data about soils at each station. Their journal entries should include:

1. The name of the station
2. The data from each station
3. The interpretation of the data from each station. For example:

• What is the purpose of these data?
• How can we use the data to characterize soil?
• What do the data tell us about where this soil came from and what the soils could be used for?
• How might I use this data collection method in my Kit?

Stations (90–120 min)

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Description:

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Soil, to many of us, is just dirt. When looked at closely, soil is composed of particles of different sizes. The particles may be rounded by alluvial action (deposited by water) or may be jagged. The soil may contain transparent crystals or even gold. A good look at soil reveals many wonders. A soil smear is used by soil scientists as a color check and is a permanent record of their investigation of that particular site or soil sample.

Materials:

Soils, hand lenses, specimen bowls, scoops, dropper bottles of water, cellophane tape

(Optional) Microscopes and slides, soil screens

Procedure

• Students view each soil sample with hand lens or microscope and write observations in their science journals (see example data sheet in methods guide). Note: Guide students to write more detailed observations by reminding them to use their 5 senses (except taste, for safety). Suggest that they note both inorganic and organic materials (e.g., roots, fungi).
• Students add soil smears in their journals by picking up a pinch of soil on a moistened thumb and rubbing the thumb in their journal. Cover smear with a piece of cellophane tape. Label each smear with collected data.

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Pore volume is a measure of the space between soil particles. In a heavy, clay soil, there is little pore volume. In a sandy soil there is a large pore volume. The pores are the pathways for water and air to penetrate into the soil. Pore volume is a soil measure that is arrived at in several different ways. All methods give an estimation of true pore volume.

Materials:

Heavy and light soils, spoons, water, 100 ml graduated cylinders, 100 ml beakers, balance scale, paper towels

Procedure:

• Weigh out a 100 g sample of soil.
• Place weighted sample into a 100 ml beaker.
• Measure 100 ml of water in graduated cylinder and pour enough water into the soil sample to just cover the surface.
• Tap the beaker to release trapped air.
• Record the number of ml of water added to the soil sample in your science journal—this is your pore volume.
• Complete activity for 1 heavy and 1 light soil sample.

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Water retention or "field capacity," as this measure is known, is one of the most important measures of a given soil to a farmer. The farmer wants to know how much water his or her soil will hold against the pull of gravity. If you have 100 g of soil and it can hold 50 g of water against the pull of gravity, the field capacity of the soil is said to be 50%. The farmer can improve this figure by incorporating organic matter into the soil.

Materials:

Soil samples, filter paper, funnel, beaker, graduated cylinder, balance scale, water

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Procedure:

• Place 100 g of soil into a filter paper in a large funnel. Place funnel onto beaker.
• Pour 100 ml of water slowly onto the soil and collect runoff in beaker.
• Measure amount of water runoff.
• Calculate water retention in ml of water per gram of soil and record data in science journal.

Optional addition: This activity could also be combined with floating organic matter in water (see optional addition in Station 5) so students can see the relationship between organic matter and water retention (organic matter aids in water retention, but this relationship is only testable if two soils are the same except for amount of organic matter).

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Water moves in all directions in the soil profile. It moves down due to gravity. Through capillary action it can move down, laterally, or up. It moves through the interstitial spaces and along the surfaces of the soil particles. It moves slowly in clay soils and rapidly in sandy soils that are more loosely organized. Organic matter absorbs moisture and holds it in place. In arid climates, the moisture wicks up in the soil profile to the point where the moisture evaporates and is lost into the atmosphere. At the point where the moisture evaporates, salts that were in the water may be deposited. These salts may make a layer that resists the penetration of water, which is called caliche. (A sample of caliche in the classroom is helpful.)

Materials:

Soil samples, coffee filters, filter paper, or cheese cloth, stout rubber bands or string, water, flat tray, stopwatch or clock with a second hand, clear tubes (100-ml plastic graduated cylinders that have the bases removed with a hacksaw work well).

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Procedure:

• Attach two coffee filters, paper filter, or cheese cloth to the bottom of a glass or plastic cylinder with rubber bands.
• Pour in soil to halfway up the cylinder. Tap gently to settle the dry soil.
• Place tubes in tray and pour 2 cm of water into tray.
• After 5–10 minutes, note how far up the water column reaches. Record data in science journal. Calculate relative speed of travel in cm/minute
• Complete for at least two soil types.

Class Discussion (30–40 min) (This may be done at the following class meeting.)

Following the soil testing method inquiry stations, return to the class discussion about soils. Expand the discussion to make connections between soil and society. This may be discussed at the end of this activity or presented as a question to ponder and then discuss in a following class session. Example questions:

• What is soil? This question works well as a minute write followed by discussion. Students write their definition of soil then discuss it in small groups. Small groups share their definitions with the class and then the class agrees on a definition. The definition of soil from the Soil Science Society of America is "A mixture of minerals, organic matter, water, and air, which forms on the land surface. Can support the growth of plants."
• How do the processes that form soil affect soil characteristics? What other processes not experienced today need to act on weathered parent material to make them soil (e.g., oxidation, addition of organic matter, interactions with animals, mechanical mixing, more erosion and weather)?
• How do soil characteristics influence soils' uses in society?
• How can what we know about soil characteristics and soil formation help us address the grand challenges facing society?
• What skills and methods were explored in this lesson? Are these skills common or unique to Earth science?
• Which skills/methods might you use to explore your chosen societal issue? Where could you find additional resources?

• How might you incorporate these testing methods in a grade-appropriate structured inquiry? How might you incorporate these testing methods in a grade-appropriate guided inquiry? Remind students that they will be developing lessons in their Kits to teach about soils.
  

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Each disciplinary core idea in the NGSS includes a relevant practice of science or engineering because students should learn science content through its practices. Pre-service teachers use some of these practices in our module, such as structured inquiry in Units 2 and 3, but more should be developed over an entire science methods course. The Kit assignment requires that at least one geoscientific practice be included in the learning objectives of each lesson. It is important to study these practices in detail before assigning the Kit and throughout an entire science teaching methods course. See Appendix F of the NGSS details science and engineering practices.

• Consider the NGSS (or those of your state). How did today's data inform your concept of Earth systems? How might you promote systems thinking in your Kit?

Lastly, use today's lesson to build on concept mapping and systems by asking students to add the new vocabulary and relationships they have learned during the maps activity to their Earth systems concept maps (started in Unit 1) following this procedure:

• Pull out your Earth systems concept map. Identify the Earth's system(s) and interacting parts of the system(s) on that map that were used in today's soil characterization activity.
  
• Identify new components of the systems that you learned today and add these to your Earth systems concept map.
  
• Discuss how a change in one system may affect another system. What are additional changes that may affect the system?

Assemble all materials for each station on a tray prior to the start of class.

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Teaching Notes:

The stations presented here mostly focus on the physical properties of soil, although stations 1, 5, and 7 address organic matter and biological processes. Minimally, students should observe organic matter in the soil and recognize that soil is a living resource formed by abiotic and biotic processes (addressed in end of class discussion). Instructors should also lead students to considering the role of organic matter in soil during individual questioning and small group/class discussions. Some roles of organic matter include: water retention, nutrient release, habitat and food for soil organisms, binding for soil particles, space for water to penetrate through soil, nutrient reservoir, etc.

If time allows, an instructor may also want to include inquiry activities focused on the biological properties of soil. The Soil Science Society of America's Biology Page lists numerous biologically-focused activities and resources, such as examining decomposition, collecting soil organisms, and examining soil using microscopes that students could use when developing their Kit.

Station 7:

The instructor must set this station up in advance (10 min). Collecting the soil with a surface layer of cryptogams is challenging. Go to a forest or range area that has had little animal or human traffic to disturb the surface of the soil. Look for soil with moss or lichens visible in the soil surface. Cut out a rectangle of soil. This rectangle of soil should hold together due to the interconnected rhizoids of the cryptogams. Slide the soil sample into the soil tray. Collect like soil without the cryptogams for the other tray. The comparison of the two samples will tell a startling tale. If you leave the soil samples in their trays you can reuse them as long as you add a little moisture from time to time.

Station 8:

• This activity uses dried soil to determine an index of relative speed of water movement in soil. It is an index of relative speed rather than actual speed because the soil has been disturbed and aggregations broken up.
• A note on materials. Any clear tube will do; 100-ml plastic graduated cylinders that have the bases removed with a hacksaw are an example of a useful apparatus. Filter paper works, but coffee filters are cheaper and work just as well. Use a shallow tray or even a beaker to hold the prepared cylinders. The wall clock in the classroom is adequate as a time keeper.
• It is important to use approximately the same volume of soil for each comparison. Slight variations are acceptable. Students will be calculating mm of water rise per minute.
• Have the students stop the activity after 5–10 minutes and record data in "mm/min" (millimeters/minute).
• Have them include implications in their journals.

Open an Internet browser, sign into someone's Google account, and go to Google Maps. In the Menu (left of the "Search Google Maps" address box), choose "My Maps," and "Create Map." You are now ready to enter GPS coordinates and save them on the map.

All points at once—fastest for the instructor to plot all of the points:

1. Enter the points into a spreadsheet (e.g., Microsoft Excel - like this one: GPS points (Excel 2007 (.xlsx) 30kB Oct16 15)) and save it to your computer. In the example spreadsheet, the "Lat,Long" column lists latitude, longitude, and the "Title" column lists the soil sample titles that you want to show up on the map.
2. Under "Untitled layer" choose "Import." Choose "Select a file from your computer" and then select your spreadsheet.
   
3. Follow the directions to select the Lat,Long column and specify the order of these to position your placemarks, and select the Title column to title your markers. Choose "Finish."

1. Type the first GPS coordinates for the first soil sample into the "Search Google Maps" box. Click the search button (blue with white magnifying glass). This should add a green pin to the map.
   
2. Click on the green pin and choose "Add to map." This should turn the pin red.
3. Type the next GPS coordinates in the directions search box and search again. Again, click the green pin and add it to the map. Now, both red pins should display on the map.
• Now that you have entered two coordinates, take a minute to predict where the next coordinate will fall on the map. What do the two numbers mean? How does changing each number affect its location? If you are not sure, try changing one GPS coordinate or the other and seeing where the new point plots (you may have to zoom out by quite a bit). Do not save these experimental points to the map.
4. Repeat steps 2 and 3 for all GPS coordinates. Check that all coordinates are plotted before proceeding. If you cannot see them all, zoom out (by clicking the minus sign in the bottom right) until you can. If you want to delete a pin, click on it and choose the garbage can.
5. Label the pins. In the box to the left, under Untitled layer, click on "Labels" and choose "description" in the drop-down menu. Now, choose "Data" and type an appropriate label name next to each set of GPS coordinates in the "description" box. For example, if your first GPS coordinates were from an alluvial soil, then type "alluvial soil 1" in the description next to those GPS coordinates. It should now read "alluvial soil 1" next to the pin for those GPS coordinates.
6. Explore the map background by clicking the downward facing arrow to the right of "Base map." Try examining your map on a satellite or terrain background. Choose the best background for your needs.

We have chosen Google Maps in this exercise because it is the most familiar to students and appropriate for young elementary students. Plotting points individually allows students to think deeply about what the GPS coordinates mean, but this is time consuming if you have many points. Middle-level students could benefit from plotting GPS points on a soils map using a computer or by hand. If students will be plotting the points, expect it to take an entire class period.

Student experience with GPS and field data collection can also be deepened by assigning students to collect the soil samples and GPS coordinates themselves. This works well as a homework assignment if you have time to train the students to use a GPS and collect soil.

Note on time management for this activity:

Going through the stations is time-consuming for many students, especially those with limited experience in following directions. Many will not get through all eight stations, even in 2 hours. One good option is to ask students to start with stations that would be most relevant to the issue they are thinking about focusing on for their Kit.

Possible Soil Misconceptions:

Soil is just dirt. Students examine soil microscopically and sort soil into different particle sizes and identify soil components and other soil characteristics.

All soil is the same. Students examine soils from different locations and modes of formation and identify the differences between soils.​
Water only travels downward in soils due to gravity. Students explore capillary action in different soils to find that water moves upward in soil at different speeds depending on soil profile.

Informal/Formative

During the station work time, the instructor should observe students working, using Socratic questioning to assist the students in meeting the goals of evaluating specific aspects of soil (learn more about Socratic questioning). Point of emphasis in questions should include 1) the purpose of each soil station; 2) how this data can be used to describe the soils being evaluated; and 3) as they progress through the stations, encouraging logical and appropriate comparisons to emphasize the "interconnections" between the stations related to a deeper understanding of soils.

The instructor should informally assess the students' knowledge and evaluation skills related to the soil investigation during class discussions. Leave time to address any commonly held misconceptions during the final class discussion.

Formal

Science journals could also be collected and graded. We typically grade the entire journal 2–3 times over the quarter. Various journal/notebook rubrics can be found following the links provided under the science journals section of "Show Pedagogic choices" under the "making the module work" section on the overview of the module. Here is a rubric that could be used to assess only the Unit 3 notes: Unit 3 Assessment Rubric (Microsoft Word 18kB Jan7 16) .

United States Department of Agriculture (USDA) Cooperative Extension System

Use this site to find a extension agent near you who can help you find local soils and may even be willing to visit your classroom.

The National Resource Conservation Service for Soils from the USDA

This site contains extensive information about soils throughout the United States and excellent background information for educators http://soils.usda.gov/education/. There are also resources for K-12 classrooms that you can share with your teacher candidates.

The Web Soil Survey from the USDA

This interactive site will allow you to view soil survey maps for your area and download soils data.

The Soil Science Society of America

This site has a number of lessons and activities (sorted by grade level) for pre-service teachers to use in the development of their Kit.