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Dirt or Soil?
Put on your boots, go outside, and dig. What do you find?
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Did you say dirt? That's true.
But you could also say soil.
Soil is the word scientists use for dirt.
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Soil All Around
Soil covers most of Earth's land. It stretches under grass and in gardens.
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Soil also lies beneath sidewalks and
roads. Sandy beaches are a kind
of soil. So are muddy riverbanks
and forest floors.
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Life-Giving Soil
Soil brings life to Earth. Plants dig their roots deep down to find water and food.
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Many animals live in soil, too.
Wriggling worms and
burrowing groundhogs
could not live without it.
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You couldn't live without
soil. Plants need soil to
grow. Animals eat plants.
Without soil, there would
be no food!
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Soil's Ingredients
So what are the magic ingredients in soil?
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Soil is made up of rocks, air, and water. Soil is also filled with what's left of dead plants and animals after they've rotted away.
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Falling leaves, twigs, and dead bugs land on the ground. As they rot, they change into rich, black humus.
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Humus might not
sound tasty to
you, but it's like
food for plants!
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But most of the
dirt that slips through
your fingers is actually
tiny bits of rock. At one time, these tiny rocks were parts of big rocks.
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How soil forms
Rain, snow, ice, and sunlight break the big rocks down into tiny pieces of rock.
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This can take thousands of years. Then the rock pieces mix with humus to form the soil you see.
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Sand, Silt, and Clay
Three kinds of tiny rocks make up soil. They are sand, silt, and clay.
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A piece of sand is not much bigger than the head of a pin.
Silt and clay are smaller still.
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Kinds of Soil
Sandy soil is coarse and loose. It won't hold much water.
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Smooth, sticky soil has lots of clay. When this soil dries out, it becomes as hard as concrete. Plant roots can't grow.
Page 19
On the other hand, soil with
a lot of silt dries out.The soil
might blow away in a
cloud of dust.
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So what kind of soil is just right for
growing plants? It has more sand
and silt and less clay. It has the
same amount of air and water.
And it is rich in humus.
Page 21
Go outside and dig again.
Is your soil dry and dusty or wet and muddy?
Do you see worms and bugs in your soil?
What is the soil like where you live?
