Is the size of particles same in different types of soil? Explain
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Soil Studies: Soil Particle Sizes
Objective: Students will learn soil size classifications (clay, silt, sand) and their effects on soil
composition.
Grade level: Elementary ‐ Intermediate
Time: First Activity ‐ 30‐45 minutes
Second Activity ‐ 30‐40 minutes
Season: Fall and spring
Materials: For each student ‐ 1 jar and a card or a piece of heavy paper
For each group ‐ 2 small tin cans (8‐12 oz.) with one end open and the other end
with many small holes in it
Marbles
Sand
Soil particles vary greatly in size, and soil scientists classify soil particles into sand, silt, and clay.
Starting with the finest, clay particles are smaller than 0.002 mm in diameter. Some clay
particles are so small that ordinary microscopes do not show them. Silt particles are from 0.002
to 0.05 mm in diameter. Sand ranges from 0.05 to 2.0 mm. Particles larger than 2.0 mm are
called gravel or stones. Most soils contain a mixture of sand, silt and clay in different
proportions.
The size of soil particles is important. The amount of open space between the particles
influences how easily water moves through a soil and how much water the soil will hold. Too
much clay, in proportion to silt and sand, causes a soil to take in water very slowly. Such a soil
gives up its water to plants slowly. These soils are sticky when wet.
First Activity Description
Have students collect some soil from their yards or from the school yard and fill a good sized jar
about 1/2 to 2/3 full with it. When they get back to school fill the rest of the jar with water,
replace the cover (tightly) and shake it vigorously.
Put the jars on a table and have the students label theirs. Allow the jars to stand for a few days
until all the particles settle out. Then hold a card or heavy piece of paper against the side of the
jar and draw a diagram showing the different layers. Label each layer (clay, silt, sand). What
percentages of each layer did you find? Which soils do you think would be better for plant
growth? How do the Adirondack soils in your jar compare with the soils in the picture? Why is
there a difference?
Size of soil particles is important for other reasons, too. It affects the ease of working the soil,
what crops can be grown, and the efficiency of certain fertilizers.
Sandy soils that have no fine clay or silt particles filling the pore space cannot hold as much
moisture since there is no surface area for the water to cling to and the pores are so large that
the weight of the water causes much of it to run down and out of the soil. For this reason,
medium and coarse sandy soils, low in clay are known as droughty soils. Crops cannot live long
in them without very frequent rains.
When fine soil particles fill the large pore spaces, the soil can hold more water for plants
because there is more surface area for water to cling to. And since the size of the pores is
reduced, the weight of the water is less and it does not run out of the soil so readily.
Objective: Students will learn soil size classifications (clay, silt, sand) and their effects on soil
composition.
Grade level: Elementary ‐ Intermediate
Time: First Activity ‐ 30‐45 minutes
Second Activity ‐ 30‐40 minutes
Season: Fall and spring
Materials: For each student ‐ 1 jar and a card or a piece of heavy paper
For each group ‐ 2 small tin cans (8‐12 oz.) with one end open and the other end
with many small holes in it
Marbles
Sand
Soil particles vary greatly in size, and soil scientists classify soil particles into sand, silt, and clay.
Starting with the finest, clay particles are smaller than 0.002 mm in diameter. Some clay
particles are so small that ordinary microscopes do not show them. Silt particles are from 0.002
to 0.05 mm in diameter. Sand ranges from 0.05 to 2.0 mm. Particles larger than 2.0 mm are
called gravel or stones. Most soils contain a mixture of sand, silt and clay in different
proportions.
The size of soil particles is important. The amount of open space between the particles
influences how easily water moves through a soil and how much water the soil will hold. Too
much clay, in proportion to silt and sand, causes a soil to take in water very slowly. Such a soil
gives up its water to plants slowly. These soils are sticky when wet.
First Activity Description
Have students collect some soil from their yards or from the school yard and fill a good sized jar
about 1/2 to 2/3 full with it. When they get back to school fill the rest of the jar with water,
replace the cover (tightly) and shake it vigorously.
Put the jars on a table and have the students label theirs. Allow the jars to stand for a few days
until all the particles settle out. Then hold a card or heavy piece of paper against the side of the
jar and draw a diagram showing the different layers. Label each layer (clay, silt, sand). What
percentages of each layer did you find? Which soils do you think would be better for plant
growth? How do the Adirondack soils in your jar compare with the soils in the picture? Why is
there a difference?
Size of soil particles is important for other reasons, too. It affects the ease of working the soil,
what crops can be grown, and the efficiency of certain fertilizers.
Sandy soils that have no fine clay or silt particles filling the pore space cannot hold as much
moisture since there is no surface area for the water to cling to and the pores are so large that
the weight of the water causes much of it to run down and out of the soil. For this reason,
medium and coarse sandy soils, low in clay are known as droughty soils. Crops cannot live long
in them without very frequent rains.
When fine soil particles fill the large pore spaces, the soil can hold more water for plants
because there is more surface area for water to cling to. And since the size of the pores is
reduced, the weight of the water is less and it does not run out of the soil so readily.
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no it varies in different soils
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