What is soil? What is soil? Soil is material that covers the earth's surface. Soil is important because
without it plants would not grow, which would not only cut off our food supply but
would create a lack of oxygen in the biosphere. Wind, rain, sun, chemicals, and other
manmade compounds often alter soil's physical and chemical properties. There are many
layers of soil, each differing in their organic composition and texture. During this week
you will learn how to obtain a sample of soil and assess its properties. There are nearly 21,000 soil types found in the United States. There are three particle sizes that make up these soil types--silt, clay and sand. Therefore, soil can be categorized into clayey, silty, or sandy soils. Soils can vary greatly in color as well. The varieties in soil color is primarily influenced by the percentage of minerals, organic matter, and elements found in the soil.
Why Soils are Important: Many people live their entire lives without ever thinking about soil. Most think of it as
"dirt," a brown, messy substance which makes clothes and hands dirty. To many it may not be important, but to others it is a crucial part of their lives. Many farmers depend on soil to provide the nutrients their crops require. Housing developers and engineers look at the soil before advancing their building plans because the soil structure has a significant role in the stability of their designs. Have you ever seen a house with a sagging roof or with
cracks in the foundation? Although these damaging effects may be due to earthquakes or other natural disasters, they may also be due to unstable soil, which can easily shift, crack, swell, shink, or even sink over time.
The Different Uses of Soil: Each type of soil has a specific use. Some soils are great for supporting massive weight,
like the soil found under skyscrapers or other large buildings. Other types of soil are
suitable for farming, such as the clayey compositions used for rice or the silty
compositions used for strawberries, potatoes, and many other plants. Other types of
soil are good for forests and wildlife habitats. During this week, you will learn how to
determine the identification and the capabilities of your soil sample by assessing its structure, depth, slope, organic matter, and chemical composition.
Picture taken from http://www.silsoe.cranfield.ac.uk/sslrc/soilinfo/level7.htm
(Note: updated URL is http://www.silsoe.cranfield.ac.uk/nsri/)
Some soils can be used for multiple applications, such as wildlife habitats and
Clay, Sand, and Silt:
Clay, sand, and silt are the three types of soil most commonly seen in soil samples.
Often a percentage of all three types of soil can be found in a sample. The different
types of soil can primarily be tested by its texture and particle size; this process will be
described later. Clay is smooth to the touch, heavy, and very thick. Soil samples with clay are
comparable to modeling clay. Silt resembles the traditional view of what dirt is. It
is lighter and resembles silly putty when wet. Sand, familiar to all, is what can be found
on a beach. Sand is manipulated much more easily than silt and especially clay.
Photo by Ron Nichols, courtesy of NRCS
Government workers Mark Kinney and Conrad Field construct a soil profile on Alaska Native
Land. Notice how they are assessing some of the soil's properties by using their hands.
With the soil sample provided, complete the following:
1. What color is the soil.
2. What is the texture of the soil? Is it smooth? Rough? Grainy? Squishy?
3. Squeeze the soil through your fingers. Does the soil appear to be saturated with water?
4. Pretend that your soil sample is play-dough. Can you build shapes with it or does it fall apart?
5. Take 1/2 cup of water and pour it over your soil sample. Does the soil absorb the water or does it run off the sample?
Hypothesis: Think about the results of your experiments.
6. What do they tell you about your soil sample?
7. Based on what you have learned today, do you think that your soil sample is a clayey, silty, or sandy
8. Based on the results of your tests, explain your hypothesis to your teacher and classmates. How much
did your results vary?
[PSSAC Home] [Teaching Unit Home] [Day Two-Student Activities]