Understanding Urban Soils
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Understanding Urban Soils

How do we determine different soil types, their functions, and the life they support?

“Next May, the yellowwood flowered early and profusely. Thousands of fragrant white blooms hung in long clusters; petals covered bricks, blew across grass. How beautiful, people said. How sad, though. Several years’ bud scars bunched up against each twig’s growing tip. Abundant flowers signaled a dying, and seeds found no purchase in the plaza. People admired the tree and walked on; they had lost the language that gives tongue to its tale. Once a yellowwood stood. No more. And few knew why.” — Anne Spirn, Language of Landscape

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This workshop is part of the 🌱Urban Ecology activity series from PLIX.

Background & Materials

Workshop at a Glance

In this workshop, we will begin to understand the diverse functions and roles of soils—the foundation of all terrestrial ecosystems—and the types of life they support. We will learn to categorize various soils and the species contained therein, and begin to unravel how urban environments shape soil structure and function.

  • Age Range: 8–13 years old
  • Group Size: 5–15 participants
  • Number of Facilitators: 1–2
  • Session Length: 2 hours
  • Cost: $8 - $10, per participant (note that materials, including hand shovels and glass jars, can be reused!)
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PLIX Tip: Remember, like all PLIX activities, we encourage you to use this guide as a jumping off point — feel free to remix it to suit your local community! And if you try something new, we'd love to hear about it on the PLIX Discussion Forum.

Supply Kit

PLIX zines—folded & cut Feeling and Soils printouts (one sheet per participant)
field journal (or any notebook) with zine holder (one per participant)
viewfinders (one per participant)
pens and pencils (one per participant)
tape — to affix clippings in field journals
hand shovels (one per 2–3 participants)
clear glass jars (for collecting soil samples, 1–2 per participant + 9–12 extra for examples)
soil samples: 9–12 of them from around your city or neighborhood (for example from your backyard, local gardens and parks, a construction site, around your library, or from your friends!)
easel pad or other large sheets of paper
outdoor protection: sunscreen, water bottles, hats, shade-structures—or ask participants to bring their own!
optional: Example soil components (loose sand, silt, and clay)
optional: Polaroid Zip Wireless Mobile Photo Mini Printer, photo paper, and smartphone
optional: printed Soil Texture triangle template (one sheet per participant)

Feeling & Soils Zine

The Feeling and Soils zine introduces the diverse functions of soil and why they are critical for ecosystem health. It also provides an outline of how to determine what a given soil sample is composed of and how these different compositions permit different types of life.

Download here →

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A note about zines: Our PLIX zines are designed to be supplementary resources for patrons and librarians to refer to during workshops. They're a quick and easy way for people to learn some fundamentals. You can print them on 8.5x11" paper, and they're easy to assemble. Here’s a resource that shows you step-by-step how to cut and fold them after printing!

Workshop Flow

Workshop Musings

  • What are the different kinds of soils that exist in our neighborhood?
  • What are they made of, and what roles do they play in our environment?
  • What does it mean for the environment if the soil is mostly sand? Mostly clay? Mostly silt?
  • How might the soil impact (or be impacted) by the surrounding environment?
  • What does the composition of a soil tell us about the type of life it can support?
  • How do urban soils differ from other types of soil?
Collecting a soil sample from the field.
Collecting a soil sample from the field.

Introductory Activity: Soil Categorization

Suggested Timing: 40 minutes

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This introductory activity will require some set-up in advance of participants' arrival. You'll need to prepare soil triangle drawings on large sheets of easel pad paper (one per small group of 2–3 participants) as well as gather ~9–12 diverse local soil samples (see Materials List).

We suggest setting your room up with workspaces for small groups of 2–3 participants. Each workspace should have one large soil triangle drawing, some pens and pencils, and 4–5 soil sample jars containing the various pre-collected soils.

Getting Started (10 minutes): When participants first arrive, hand out copies of the Feeling and Soils zine and make sure everyone has their field journal. Encourage participants to pair-up and spend 5 minutes looking through the zine. They should discuss amongst themselves any questions or observations they might have. Next, using the zine as a jumping off point, spend another 5 minutes as a full-group discussing the functions of soils, why they are important, and the different components that make up soil (sand, silt, clay).

Soil Categorization Demos (10 minutes): Introduce soil triangles. Demonstrate (with hands-on examples) two different methods for categorizing soil—touch testing and soil shakes.

Small Group Exploration (20 minutes): Have participants work in their small groups to categorize the group's 4–5 soil samples by first using the touch test method and placing them on the soil triangle. Then let participants add water to their soil jars, shake, and let them settle a bit before comparing results.

Group Discussion (10 minutes): Let each group share out a little about how they categorized their samples—what was their thought process? How did they decide where to categorize the soil? What did the different tests reveal?

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PLIX Tip: We recommend numbering your pre-collected sample jars and keeping a separate master list of the types of sites they were collected from (e.g. your garden, a construction site, a local park). After participants characterize the various samples, you can reveal where they came from and discuss further. It's also a good idea to give different small groups some of the same samples, so they can compare their categorization results. How did different groups categorize the same soil? Was there consensus? Why or why not?

A simplified version of the soil triangle—a tool used to determine the percent composition of sand, silt, and clay in a given soil sample.
A simplified version of the soil triangle—a tool used to determine the percent composition of sand, silt, and clay in a given soil sample.
Example soil characterization using the (more complex) USDA’s Soil Texture Triangle. For older participants, it may be useful to have this
Example soil characterization using the (more complex) USDA’s Soil Texture Triangle. For older participants, it may be useful to have this full version of the soil triangle printed out and on hand in case they are interested in a more comprehensive quantitative analysis of their soil samples.

Your participants may want to create their own classification using this blank Soil Texture template.

PLIX-Soil-Texture-Triangle-Template.pdf191.3KB
https://drive.google.com/file/d/1EGvNB4-NrKEIny4dB_o_LAgh0_SiajU5/view?usp=sharing

Categorizing soil with touch testing

There are two quick and simple ways to categorize soil with touch testing: First, by creating soil 'rubbings' on paper (to assess soil particulate size), and second by clumping the soil together using our hands (to assess soil moisture).

To complete a soil rubbing, place a few pinches of soil in a small mound on a sheet of paper. Using your fingertips, rub the soil into the paper until it is separated as much as possible, into its smallest components (this will often leave a cast on the paper). Sand, silt, and clay have different particle sizes, and so you can use this test to estimate the size of the particles present in a given sample (particles will also have different textures depending on their relative size).

Participants use touch testing methods to categorize soil in their soil triangle.
Participants use touch testing methods to categorize soil in their soil triangle.

To complete a clump test, fill your palm with the soil sample and compress it by closing your fist. Squeeze as tightly as you can! Then, open up your hand and see how well the soil sticks to itself. Moist soils will clump easily, forming a ball, while dry soils will not hold any shape. Soils with smaller particular sizes are able to grab onto water more easily — clayey soil holds the most water, while sandy holds the least (with loamy soil holding an amount somewhere in-between).

Categorizing soil with soil shakes

A soil shake test can show you the different elements that make up a soil. After separation of the soil components, you can also cross-reference the relative composition of a given soil sample with your soil triangle predictions from touch testing.

How to run a soil shake test:

  1. Collect some soil in a jar (fill it about 1/3 with soil) and then fill the remaining space with water.
  2. Tighten the cap and give the jar a good shake for about 30 seconds.
  3. Let the jar sit, undisturbed, for up to 48 hours (though you will see some stratification in only a few minutes!).
  4. After letting your jar sit, you'll notice the soil separate into 3 distinct layers—the bottom layer is sand, the middle layer is silt, and the top layer is clay.
  5. Calculate the % of each layer in the soil, and use the soil triangle to determine what kind of soil it is.
How to read a soil shake jar — a page from the
How to read a soil shake jar — a page from the Feeling and Soils zine.

Field Exercise: Collecting Soil Samples

Suggested Timing: 50 minutes

For this field exercise, participants will visit two field sites, differing in the type of vegetation they have (e.g. a basketball court next to a construction site and a landscaped courtyard), collecting a soil sample as well as a plant specimen (or the image of the plant if it's not possible to collect) at each site.

We recommend having your group divide up into teams of two or three. Each team gets a shovel and 3-4 empty jars for collecting soil samples. Make sure participants bring their field journals with them to record observations of the types of life found near each soil sample site. As a facilitator, you may also want to have a camera (and mobile photo printer, if you have one!) for snapping some photos.

Collecting a soil sample near the fence of a small construction site.
Collecting a soil sample near the fence of a small construction site.

The goal of the exercise is to collect diverse soil samples from your two field sites, as well as document the type of life that soil supports. For example, if you find a street-adjacent compacted soil sample, dig a few inches down to collect the soil itself, but also collect a spontaneous urban species growing in it. If there is nothing growing in a soil sample, make a note of that in the field journal (this condition is equally telling of the health of that soil sample). If the species is too large to collect (for example, a tree), take an image of the life form fostered by the soil, or utilize another form of method like bark rubbings or drawings.

Do some on-site analysis in the field: clump the soil together in your hands; predict how well or not it might retain water; predict its relative composition of clay, silt, and sand; try to imagine how this sample of soil is changing over time—what is its future or past?

Clumping soil can give you insight to its composition and function!
Clumping soil can give you insight to its composition and function!
For example, this soil sticks to itself quite well, forming a ball when compressed. This result indicates that the soil retains moisture well, and is most likely made of largely of clay.
For example, this soil sticks to itself quite well, forming a ball when compressed. This result indicates that the soil retains moisture well, and is most likely made of largely of clay.

Clump test on coarser soil . . .
Clump test on coarser soil . . .
This soil is far more dry than the above example! Notice that it does form as uniform a clump, meaning that it is drier and does not hold water as easily as clay-heavy soil.
This soil is far more dry than the above example! Notice that it does form as uniform a clump, meaning that it is drier and does not hold water as easily as clay-heavy soil.

Come-Together: Soil Show & Tell

Suggested Timing: 30 minutes (20 min for the activity + 10 min for clean-up & hand-washing)

For the come-together activity, we recommend staying outside (weather permitting), perhaps using a picnic table or shady area to sit down together as a group.

Before starting, have each small group perform a soil shake by adding water to each of their collected soil samples. This way, the soil can start to form some initial layers by the time this activity ends. We also let participants take their soil jars home with them for evaluation after they've fully settled.

Then, have each small group of participants show & tell about their collected soil samples, where they came from, what types of species they found growing nearby, and some guess as to what type of soil they think it might be. Use the prompts below for some further discussion!

Prompts for Show & Tell Discussion:

  • Which types of soil did you encounter most in your sampling? Wet, clay-heavy soil? Sandy, dry soil? Rich, moist, and smooth soil?
  • What patterns did you notice between the type of soil you found and how deep or wide you dug your hole?
  • What types of plants grew in the types of soil that you collected? If there were no plants growing there, can you guess why?
  • Can you notice any patterns between types of soil you collected and the type plants growing in it? (For example, did taller plants grow in sandy soil? Did flowers grow in clay-heavy soil?)
Adding water to soil samples for soil shakes!
Adding water to soil samples for soil shakes!
Participants show & tell about their various soil samples, roundtable-style.
Participants show & tell about their various soil samples, roundtable-style.
A participant shares clippings of the organisms found in and around their soil samples.
A participant shares clippings of the organisms found in and around their soil samples.

Some soil shakes settling out during group discussion.
Some soil shakes settling out during group discussion.

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