Examination of soils and rocks – lab
AP Environmental Science
As you have learned by reading the text, soils are a complex mixture of organic and inorganic material:
minerals and chemical compounds eroded from rock, and organic compounds produced by decomposition
of living things.
Various factors affect the chemical, biological, and physical nature of soil. The pH of soil is an important
factor in determining which plants will grow because it controls which nutrients are available for the
plants to use. Three primary plant nutrients – nitrogen, phosphorus, and potassium – are required for
healthy plant growth. Because plants need them in large quantities, they are called macronutrients. They
are the main ingredients of most fertilizers that farmers and gardeners add to their soil.
Plant Nutrients
Macronutrients Micronutrients
Nitrogen
Iron
Phosphorus
Manganese
Potassium
Zinc
Sulfur
Copper
Calcium
Molybdenum
Magnesium
Cobalt
Chlorine
Other nutrients such as iron and manganese are also needed by plants, but only in very small amounts.
These nutrients are called micronutrients. The availability of these nutrients depends not only on the
amount but also on the form that is present, on the rate they are released from the soil, and on the pH of
the soil. In general, macronutrients are more available in soil with high pH and micronutrients are more
available in soil with low pH. Figure 1 shows the effect of pH on the availability of nutrients in the soil.
In today’s lab you will conduct a variety of observation-based tests. Record all the information in your
notebook, and use it to type up your lab report.
Part I: observation of rocks
Available for your observation is a box containing 50 samples of rocks and minerals. Examine at least 5
of these samples. Record your observations about the appearance and texture. Use the accompanying
guidebook to note the chemical nature and geologic origin of the samples that you examine.
Examine the three samples of coal types. Describe the appearance, color, and consistency of each.
Part II. Physical characteristics of soil
Use the soil sample that you collected for these observations. Be sure to note the specific location from
which your soil was obtained.
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Using the “geotechnical gauge”, describe the type of particles found in your soil sample. Note
the color, particle size, and other characteristics that you observe.
Examine the soil core obtained by Mr. A. Sketch its appearance. In your report, compare the
sketch of the typical soil profile shown on p. 68. Describe the three horizons in a typical
soil. Were you able to observe all of them in the profile?
Use the web site http://soils.ag.uidaho.edu/soilorders/index.htm to study the characteristics of the
12 soil orders. Give a brief description of each type. Use the map at
http://www.nrcs.usda.gov/technical/land/lgif/m4025l.gif to determine the type of soil most likely
to be found in the DC region. Read the more detailed description of this type of soil, and
summarize what you learn. Check out the global distribution of your soil type – where else is it
located? (try here if the link does not work)
Observe the procedure for determining soil texture – the percentage of sand, silt, and clay in your
sample. We will use the procedure on just one of your samples, since we don’t have the
equipment or time to examine all the samples.
Soil texture data:
Percent sand
Percent silt
Percent clay
Chemical tests - pH:
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place a heaping teaspoon of soil in the center container
Use a pipet to add just enough distilled water to saturate the soil, then add 5 more drops. Let the
soil sit for 30 seconds
Use the spoon to press the soil to the side of the plastic container and release the water. Take a
strip of pH indicator paper and dip it in the water. Match the color to determine the pH.
Soil biology
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Browse through the soil biology primer
(http://soils.usda.gov/sqi/concepts/soil_biology/soil_food_web.html). Summarize what you learn
about soil biology and food webs. Discuss carbon sequestration, bacteria, fungi, and other living
things.
Use the “SK Worm” site http://www.nrcs.usda.gov/feature/education/squirm/skworm.html to
learn about soil basics. Print out a copy of the certificate at the end to use in your lab report.
Your lab report should be typed. Include all of the observations that you made during the lab, as well as
the computer-based research on soil types. Discuss the significance of what you learned: why is soil type
important? What human endeavors depend on knowing something about soil? Describe some
environmental problems related to soil.