Soil Properties

Soil Properties Overview

Even though you might not have thought about it before, there are many types of soil and they can be very different from each other. Soil can be sticky, slippery, or crumbly. It can be smooth or gritty. It can be brown, black, gray, tan, or red. Some of the different characteristics of soil have an impact on what kinds of organisms can live there. How, you ask? You've come to the right place to find out!

What Are We Doing?

In these five activities, students will collect data about the physical properties of the soil at their field site. Their investigations will enable them to figure out what type of soil it is. All of the activities in this section use the following worksheets:

  • Texture Test
    In this activity, students will determine the composition of the soil by feeling the texture of the soil. They will then use this information to classify the soil as sand, silt, or clay. Time: 30-45 minutes
  • Mud Shake
    In this activity, students will determine the composition of the soil by separating the soil particles into layers. They will then classify the soil as sand, silt, or clay. Time: 15-20 minutes over two days
  • Soil Temperature
    In this activity, students will measure and record the soil temperature at their field site. Time: 15-20 minutes
  • Compaction Test
    In this activity, students will measure and record how far a pencil can be pushed into the soil at their field site. They will use the data to infer the degree of compaction of the soil. Time: 15-20 minutes
  • Percolation Test
    In this activity, students will measure and record how long it takes water to soak into the soil at the selected field site. They will use the data to infer the degree of compaction of the soil. Time: 45-60 minutes

How Does This Help Our Inquiry?

Before beginning these activities, remind students of the research question—What is the relationship between the soil's physical properties, environmental and human factors, and soil biodiversity?—or the research question that they posed instead. As they do the activities, ask students to consider how each relates to their research question. Depending on your research question, you may elect to do only some of the activities in this section. If you do intend to do several or all of the activities, you may choose to introduce only one or two activities each field visit for the first few visits. Once students have had practice with each of the activities, they should be able to complete multiple activities in a field visit. The activities should be done in the same location each time they are done. If possible, students should do the activities at the same time, or do them at the same time of day on different days. Doing this allows students to control the variables of time and location. You may also give students the opportunity to identify and find ways to control other variables that could affect the outcome. This topic is also addressed in the summary exercise. Students should keep all of their data and observations in their field journal to facilitate comparison. They can also experiment with different ways to display their data for easy comparison, such as creating their own charts and graphs.

In each of these activities, students will gather data about the soil. Students can compare this data and the data they gather in Looking for Life and Rock Flip. This will help them to see the relationship between soil type and soil biodiversity. Some connections they can make with this data include:

  • How soil compaction affects the critters that can live in the soil.
  • How soil temperature affects the critters that can live in the soil.
  • How soil texture/type affects the critters that can live in the soil.

Students can also compare the data they gather in these activities and the data they gather in Factors That Affect the Soil. This will help them to see how a variety of factors affect the properties of soil. The factors that affect the soil can also affect what lives in the soil. Some connections students can make with this data include:

  • How soil temperature relates to air temperature and cloud cover.
  • How soil compaction relates to food source habitats.

For additional experience with the scientific method, students will be asked to form a hypothesis around a given question for each activity. The questions posed in each activity are very basic and are structured so that they can be answered in one session. They can serve as a simple way to introduce students to the activity, before they begin using the tests as part of their field study. For the best learning opportunities, however, students should return to the field site repeatedly to conduct these tests over a period of time. This will allow them to record how changes in temperature and season affect the soil, as well as note the impact any human disturbance might have. The questions for each activity can easily be tailored to reflect this extended study or to directly reflect your research question. For example, if students will be doing both soil temperature and air temperature activities, you may ask them to hypothesize whether or not the two temperatures will be similar.

Before students begin these activities, hand out the Soil Properties Overview worksheet and have students place it in their field journals. Students can use this worksheet to analyze the data they have collected in the field. You may choose to have them do this analysis after each visit to the field or after they have completed several sessions. The Big Picture section of the worksheet prompts students to make connections between the activities in the different sections.

Background Information

Soil Structure
The soil we see around us is made up of small pieces called particles. Soil particles form clumps called aggregates. Soil structure refers to the way soil particles of different sizes are clumped together.

Soil Particles
There are three different types of soil particles—sand, clay, and silt.

Particle descriptions
Sand particles are the largest and heaviest particles.
Silt particles are middle size and weight.
Clay particles are the smallest and lightest particles.

Spaces in Soil
When soil particles form aggregates they leave spaces for air and water to get into the soil. Air and water are vital for everything that lives and grows in soil. These spaces are where tiny living things such as plant roots, microorganisms, insects, and fungal hyphae are found. The amount of spaces in the soil depends on the type of soil. A sandy soil will have lots of spaces, and a soil high in clay will have fewer spaces.

Investigating Soil Structure
Compaction describes how tightly the spaces in the soil are packed together. Soils that are highly compacted have fewer spaces for air, water, and living things.

Percolation describes the movement of water through the soil. Percolation is another measure of the amount of compaction of your soil. The faster the water runs through the soil, the less compacted the soil is.

The texture of a soil refers to the particle sizes found within it. Remember that most soils are composed of a mixture of different-sized particles. The three main categories of soil particles are sand, silt, and clay. These three particles can exist in a soil in almost any combination. Soil scientists classify different types of soil by both their texture and color.

Making Connections

Soil structure and soil type can affect the diversity of critters that are found in the soil. If the soil is made mostly of clay, for example, it has less space for air and water. Less space for air and water means fewer living things can be found in the soil. Living things help to nourish soil and make it healthy.

Healthy soil is important to us for many reasons. Without soil, we could not eat breakfast. Everything from the wheat in cereal to the oranges in juice to the animal proteins in milk, bacon, and eggs were nourished by the soil and what grows in it. Believe it or not, without soil, we couldn't wear blue jeans! Jeans are made of cotton denim stitched together with cotton thread. Their blue color comes from indigo dye. Cotton and indigo come from plants that need soil to grow.

If you wanted to grow a garden at your school, it would be important to know what kind of soil you have. Soil with too much sand or clay would not be good for growing plants. You might need to add special soil for the plants to grow.

General Tips

  • Be ready for dirt! You may want to have students bring an extra pair of shoes to wear while they are doing field work. They can change shoes before going outside and then leave those dirty shoes at the door when they return to the classroom.
  • Remember to do the soil study at the same location and time of day each time.
  • Be prepared to do the activities in Soil Biodiversity and Factors That Affect the Soil at the same time and place as these activities.
  • Be sure students bring their field journals, writing utensils, all necessary data sheets and—if possible—clipboards so they can record their data and observations.

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