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Soil: The Wealth Beneath Your Feet
Purpose: To test and compare soils from around the United States
Background: Unless you are a farmer or gardener, you probably think of soil as “dirt” or something you do not
want on your hands, clothes or carpet. Yet, your life and the lives of most other organisms, depends on the soil.
Soil is not only the basis of agricultural food production, but is essential for the production of many other plant
products such as wood, paper, cotton, and medicines. In addition, soil helps purify the water we drink and is
important in the decomposition and recycling of biodegradable wastes.
Nations, including the United States have been built on the riches of their soils. Yet, since the beginnings of
agriculture people have abused this vital, potentially renewable resource. In fact, entire civilizations have
collapsed because of mismanagement of the topsoil that supported their civilizations. Today, we are not only
facing loss of soil from erosion, we are also depleting nutrients in some soils and adding toxins to others.
Hypothesis: Describe where your soil came from. Rate the fertility of your soil on a scale of 1 to 5 with 5 being
excellent for growing plants. ____________________________________________________________________
___________________________________________________________________________________________
Procedure: You will perform the following lab tests on your soil to determine the plant growing capacity. You
will then rate the soil on a scale of 1 to 5 and compare it to your hypothesis. The following tests can be done in
any order, but you need to pay attention to time and plan your experiments so as to complete all them in the time
allotted.
Hints for a successful lab:
 Plan your time wisely. Some activities require a sample to sit for ten to thirty minutes. Begin a new activity
while waiting for another activity to finish.
 Read the instructions with the soil testing kit carefully.
 Do not put soil down the drain. It will clog the pipe. Rinse the mud and water into a five gallon plastic bucket
to be discarded outside.
Prepare the soil samples
1. Remove about 40-50 mL of the soil sample and set it aside for determination of the soil texture (day 1).
2. Spread out the rest of the soil onto a sheet of paper to dry for chemical analysis (day 2)
3. Remove unwanted foreign material from the soil such as twigs, leaves, and stones.
4. Crush the soil gently to break up any clumps.
5. Dry the soil dry until it is ready to be used.
Activity 1: General Observations
Take a sample of soil and place it on a piece of paper. Then, using a dissection microscope, look closely
at your soil sample. What do you see? Record any forms of organic matter you might see (roots, worms,
insects, etc.). Observe the various particle sizes – which are the most abundant?
General (color, odor)
Observations
Particle Size
Abiotic Factors
Biotic Factors
Test 1: Soil pH
pH refers to whether a substance is acidic or basic. The scale ranges from zero to 14. pH of 7.0 is neutral with
values < 7.0 being acidic and values > 7.0 being basic. pH affects the availability of nutrients to plants so
therefore can be used to determine the production potential of the soil. Low pH levels prohibit plant growth. Soil
with low pH levels can be treated with lime to increase pH and hence increase plant growth. pH preferences of
plants can vary, though for most plants the desirable pH range is 6.0 – 6.5
Follow the directions in the soil test kit to test the pH and record the pH.
Data: pH______________
Questions:
1. Was your soil acidic, basic or neutral?
2. What did the pH tell you about the fertility of the soil?
3. How does pH influence the fertility of soil?
Test 2: Soil Texture
Soil texture is a soil property used to describe the relative proportion of
different grain sizes of mineral particles in a soil. Particles are grouped
according to their size into what are called soil separates. These separates
are typically named clay, silt, and sand. Soil texture classification is based
on the fractions of soil separates present in a soil. The soil texture triangle is
a diagram often used to figure out soil textures.
Methods:
1. Place 25ml of your soil sample into a 100 ml graduated cylinder.
2. Fill the graduated cylinder to about the 75 ml line with water.
3. Cover the cylinder with film and invert several times until the soil is thoroughly
suspended in the water. Place the cylinder on the lab station and leave it to settle
overnight
4. When the soil has settled out, there should be 3 distinct layers. Measure the volume of each layer and
the total volume of the sample.
5. Calculate the percentage of each component.
Amount of each component
x
100 = % component
Total volume of soil
6. Identify the type of soil in your sample by using the soil texture triangle. Sand looks like distinct
particles, silt is small and gritty, and clay is uniform in color. Ignore the humus (organic matter). Sand
will be on the bottom, silt in the middle, and clay on the top.
7. Record your result in the Table.
Total soil
column
Volume of soil sample
(ml)
% of total
Sand
Silt
Clay
100%
soil column
Questions:
1. What type of soil do you have?
2. Why do you think the clay and silt settled on top of the sand?
3. The material floating near or on top of the water is organic material called humus. Why do you
think it is floating near the top of the water column?
Test 3: Nitrogen
Nitrogen is a part of every living cell. As a component of amino acids, the building blocks of proteins,
nitrogen is a vital link in the world’s food supply. Nitrogen is directly involved in photosynthesis. It
stimulates above ground growth and produces the rich green color characteristics of healthy plants.
Nitrates, the available form of soil nitrogen, are produced through the decomposition of organic matter,
the application of nitrogen fertilizers, and the fixation of atmospheric nitrogen by microorganisms in the
roots of legumes. Soil nitrogen is depleted through harvesting crops, leaching by rainwater and
denitrification.
Methods: Follow the procedure in the soil test kit.
Data: Nitrogen level:___________________
Questions:
1. Why do you think you got the results you did on the nitrogen test?
2. What could you do to fix it?
Test 4: Phosphorus
Young plants absorb large amounts of phosphorus, which speeds seedling development and promotes
early root formation. Rapid, early growth means hardier, stronger plants. In mature plants phosphorus is
vital to the development of healthy seeds and fruit which contain large amounts of this essential nutrient.
Only a small percentage of soil phosphorus is in available form and these phosphates move more slowly
through the soil than other nutrients.
Methods: Follow the instructions in the soil test kit.
Data: Phosphorus Level:______________________
Questions:
1. What does mean to say that the phosphorus is not in an “available” form?
2. Why is phosphorus often a limiting factor in ecosystems?
Test 5: Potash (Potassium)
Potassium plays a vital role in the physiological and biochemical functions of plants. It is absorbed in
large amounts by plants. It is used to build proteins; increases resistance to disease by strengthening
stalks and stems; increases cuticle (waxy layer) to prevent water loss; helps prevent wilting; and
enhances fruit size, flavor, texture, and development.
Methods: Follow the instructions in the soil test kit.
Data: Potash Level:____________________
Questions:
1. Besides fertilizer, how does potassium get into the soil?
Cleanup lab
 Dump unused soil in an appropriate area outside or in provided container.
 Soil used for the chemical tests should be placed in an appropriate area outside or in provided
container. Do not put soil down the sink!
 Return equipment and soil test kit materials to your teacher.