The relationship between texture and soil function
Soil texture can determine a soil’s ability to perform different functions in the environment, for example some soil textures may be good for root growth while others may be good for absorbing rainwater. after a storm. These functions are important to ecosystems and the way humans interact with soil in their environment. The best uses for each type of soil can be determined based on its texture and components.
WARNING: Be prepared for your dirty hands!
Click on the link to create a copy of the Soil Survey Worksheet.
Prepare: collect and observe the soil
The first step in studying the texture and components of the soil is to choose and obtain a sample of the soil that you want to study.
- Decide where you are going to collect your land.
- Depending on where you choose to collect the soil, what do you hope to find there? Write down some of your ideas on your Soil Survey Worksheet.
- Use a small shovel to dig the first two inches of the soil and place the soil (about a cup) in a plastic bag. This soil will be used in the next two activities.
- Add location information and sightings to your Soil Survey Worksheet. Make sure to add contextual information about the region. What is the zone used for? Is the surface of the ground bare or covered with grass? Can you see anything alive in the ground as you dig for your sample?
- Take a look at your sample and write down your observations. What colors do you see? (See this color reference.) Do all particles look the same? Is it lumpy? Can you see living things there?)
As we learned above, the matrix of a soil has four main components. Specific components are often dictated by the location of the soil and are directly related to the role it plays in an environment. You have your soil sample, let’s find out now!
Use your Soil Survey Worksheet collect your observations during each of the following surveys.
First step: visual examination
Let’s start by looking at the soil sample you collected. Look at it with a magnifying glass, touch it, smell it. What observations can you make of it?
- What did you find in your soil sample?
- Have you noticed any particular shapes, colors or textures?
- Is there something alive in it?
The next two activities get complicated, so cover your work surface with something that you can wash or throw away easily.
Second step: shake test
One of the characteristics of soil type is texture – the ratio of mineral components in a soil sample. Let’s separate the different types of minerals in a soil sample and determine the percentage of sand, silt and clay. Before you begin, divide your soil sample into two parts, place one half of your sample in a jar, and leave the other half in a plastic bag for the next soil texture experiment.
- Fill a glass jar halfway with the soil from your sample. Fill the remaining half of the pot with water.
- Tighten the lid on the pot and shake until the soil and water are well mixed.
- Place the pot on a table and let the soil sit for 1 to 2 minutes. (This time is sufficient for your observations, but you can leave the sample overnight to allow the sediment to settle completely.)
- Mark the top of each level of soil on the pot using a wet or dry erase marker.
- Measure the distance from the bottom of the pot to the first mark in inches. These are the sand particles. Note the distance on your Soil Survey Worksheet.
- Measure the distance between the first mark and the second mark. These are the silt particles. Note the distance on your Soil Survey Worksheet.
- Measure the distance between the second mark and the third mark. These are the clay particles. Note the distance on your Soil Survey Worksheet.
- Measure the distance from the bottom to the third mark from the bottom. This is the total soil sample.
- Convert fractions to decimals and write them on your Soil Survey Worksheet.
- Calculate the percentages of sand, silt and clay for the sample. For example, divide the distance from the mark from step five for sand by the total distance from the sample from step eight, then multiply by 100. This will give you the percentage of sand in the sample. Repeat for the clay and silt.
- Use the Ground texture triangle to determine a more precise description of the soil texture based on the percentage of sand, silt and clay.
The Soil Texture Triangle allows you to use the fractions you just identified to describe your sample and determine the soil texture. You can even see how the percentage of sand, silt, and clay in your soil sample compares to the ratio of mineral types in other soil textures!
Questions for reflection
- What do you notice about the different layers in the pot?
- What is the percentage of sand?
- What is the percentage of silt and clay?
- What is the texture of the soil in your sample, based on the texture triangle above?
- Draw a picture of the soil particles as they appear in the jar
Third step: ball and tape test
Soil texture mixes can be graded by touch as well as sight. When you looked at the Soil Texture Triangle, you probably noticed that when different ratios of particles mix together, the resulting soil textures are different. Soil scientists use two additional tests, the bale test and the tape test, to help them better describe the texture of soil samples.
You will perform these tests using the flowchart and video below to describe the texture of your soil sample in more detail. Use the flowchart and videos to help you complete each test.
Use the Ball and Ribbon Flowchart (photo below) to determine the texture of your floor to the touch.
You can use this UC Davis soil test video for more information on how to do the ball and tape test.
- How did the soil in your sample feel?
- What particle sizes have you noticed?
- What was the texture of your soil sample based on the above test flowchart?
“… If you think of the ground, it’s kind of a matrix of particles. And these aggregates are really essential to have a good space in the soil for the roots to grow, for the water to seep in. —Andrea Basche, Science Friday 2018