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, you will collect data about the physical properties of the soil in your field site. Your research will help you figure out what type of soil it is. All of the activities in this section use the following worksheets:

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

Want more information before you get started? Read on to find out:

How Does This Help Our Inquiry?

Remember our research question—What is the relationship between the soil's physical properties, environmental and human factors, and soil biodiveristy?—or the research question you asked instead. In each of these activities, you will gather data about your soil. Look at the data you gather in these activities and the data you gather in Looking for Life and Rock Flip. This will help you to see the relationship between soil type and soil biodiversity. Look at the data you gather in these activities and the data you gather in Factors That Affect the Soil. This will help you see how a variety of factors affect the properties of soil. Be sure you do these activities in the same location so you can compare the data you get. If possible, do the activities at the same time, or do them at the same time of day on different days. Do these activities as many times as you can. The more data you collect, the easier it will be to see the relationships between soil biodiversity and soil type.

Before you begin these activities, print the Soil Properties Overview worksheet sheet and place it in your field journal. After you complete each activity, use this sheet to summarize and analyze your results. When you have completed all of the activities in this section, fill in the Big Picture section of the summary sheet.

What Do We Need to Know?

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.

Why Is This So Important, Anyway?

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 to get dirty! You may want to bring an extra pair of shoes to wear while you are doing your field work. Soil study can be messy!
  • Remember to do your 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 to bring your field journal so you can record your observations and all the data you gather.

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