Back image: Viking Lander (near the Martian Equator)
Inset image: Mars Pathfinder Mission (near the Martian Equator)
In addition to sunlight, water, and carbon dioxide most plants prefer to have some soil for their roots.
Not all plants like the same kind of soil. For example, one type of plant may grow best in a dry sand-like soil, another type of plant my prefer a wet clay-like soil.
There are two qualities which characterize soils:
Back image: Viking Lander (near the Martian Equator) |
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Notice how closely the photo to the left (from Devon Island in the Canadian Arctic) physically resembles the image shown in the two Martian images above.
Are they soil? Are they similar?
The question can only be answered definitively by careful analysis of a sample from each location.
In this activity we will learn how to perform a physical analysis of a soil sample and then compare our results with soil samples taken and analyzed by other groups.
The chemical analysis of soils can be complex. Determining the physical characteristics of soils, however, is fairly straight forward.
Determining the physical characteristics of a soil involves a determination of what fraction of the soil is made up of particles of a specific size and the ratio of organic matter (decaying plants, leaves, roots, and microscopic organisms) to inorganic matter (rock).
For example, gravel is largely made of small pebbles and broken stone with a small amount of finer rock we generally call sand and almost no organic matter. Black garden loam on the other hand is almost all sand with a large amount of decaying organic matter plus a small amount of very fine stone similar to clay.
Divide your class into teams or small groups. Assign each group a location from which to collect a soil sample. [About 1/2 a paper cupful is sufficient] Some suggestions would be to collect a soil sample from:
A soil analysis system can be constructed easily from a stack of large paper cups.
The bottoms are cut out of each cup, then the holes are covered with material which acts as a filter. Sturdy elastic bands hold the filter material over the bottom of each cup.
The diagram to the left provides some suggestions as to the materials that can be used as filters.
The cups are stacked in order, the finest filter on the bottom and the coarsest on the top.
To analyze a soil sample, mix the sample thoroughly with an equal amount of water. Stir the mixture vigorously to produce a pourable mixture.
Pour the mixture slowly into the top cup. Continue until the original sample of soil has all been poured into the stack of filters.
Rinse the system with about 200ml of clean water while gently "bumping" the stack up and down on the desk top.
Allow several minutes for all the excess water to drain from the system.
HINT: This is a "messy" exercise. Have plenty of paper towels available and cover desk tops with old cloths or used newspapers.
Once most of the water has been drained from the filter system the residue trapped by the filter in the bottom of each cup can be examined.
An excellent way to do this is to invert each cup onto a coffee filter and bang the cup gently to shake out the residue onto the coffee filter.
Label each coffee filter paper from 1 to 5 (in order from top to bottom of the filter system) and empty the cup on the appropriate number.
Allow the residue to dry overnight to remove all excess water.
Using a magnifying glass, examine the characteristics of each sample.
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Have students make a bar graph according to the relative amount of each type of residue. Assign the number one (1) to the least abundant, and five (5) to the most abundant. Plot the results on a bar graph as shown in the images below.
Compare the bar graphs drawn by other groups sampling the same type of soil and groups sampling other types of soil.
