Soil, is made from rocks that break apart or wear away
over many years. This is referred to as weathering. It may
take 100 to 1,000 years for 1 cm of soil to form through weathering.
Soil also contains air, water, and humus, the decayed remains of dead
animals and plants.
Soil can actually be separated into 5 main parts.
They are:
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Humus: A dark, moist soil composed of bits of dead,
rotting insects, animals, leaves, roots, sticks, and food. Humus
adds nutrients to the soil which plants need to grow and live.
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Clay: A soil that holds water. When wet, clay
feels slippery and slimy. It is made of particles that are smaller
than 0.004 millimeters.
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Silt: Soil that looks like fine grains or tiny pieces
of rock. Particles classified as silt measure from 0.004
millimeters to 0.006 millimeters.
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Sand: Soil that is coarse and drains quickly.
Sand particles measure from about 0.006 millimeters to 2.00 millimeters.
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Gravel: Visible rock particles, sometimes referred to
as pebbles.
The vast majority of all organisms living in the soil
are "good guys," helping to:
Because nature does not always provide the best type of
soil for the crops farmers want to grow, they plow , add fertilizers,
and irrigate to help the good micro-organisms create a healthier growing
environment. Scientists are using Global Positioning Systems
technology to map and analyze soil in the field so that farmers apply
just the right amount of water and fertilizer.
While most organisms in the soil are good, a few are bad
and can hurt crops.
One "bad guy" is a fungi called
Cercospora Beticola that
attacks sugar beets. At the Northern Plains research lab in
Sidney, MT, scientists are studying ways to fight C. beticola using
"friendly fungi" that lives in the soil. These friendly fungi - called
Laetisaria arvalis - release an enzyme that prevents C. beticola from
getting the food it needs, essentially starving the bad fungi and
preventing the disease from occuring.
Sidney scientists are also studying ways to increase the
number of another beneficial fungi found in the ground that helps to
aggregate the soil and may also aid in weed control.
Soil! Without it we would be naked, homeless and
starving. Although we rarely notice the soils around us, we rely
on them to produce our food, clothing and shelter; to clean our water;
to play on and in, and as a solid base for our buildings.
Soil is our greatest resource, yet every year soil that
could be growing crops or pastures is lost or damaged by erosion,
contamination and overuse or misuse.
Scientists at the Northern Plains research lab in
Sidney, MT, are studying ways to improve, maintain and save our
agricultural soil through both biological and mechanical methods.
Some of those methods include no-till, minimum till, and conventional
tillage with different crop rotations to preserve nutrients in the soil.
Protozoa and Bacteria:
Protozoa are very small one-celled creatures. They
play an important role in helping to make the soil better by feeding on bacteria
and releasing excess nitrogen, which is really good for plants. Bacteria are
among the tiniest and most numerous organisms in the soil.
They decompose dead organic matter and convert it
to nutrients, which is food for plants. Notice at the right the
little specks of
bacteria all around the oval protozoa and large, angular sand particle.
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Fungi:
Fungi is also very small, numerous in the soil, and works along
with bacteria in breaking down dead matter found throughout the soil.
Fungi, bacteria, and plants work together to help each other
survive. Fungi takes out some nutrients from the soil to help
the plants grow better, while
the plants provide the fungi with carbon and energy by attaching
to the plant's roots. The fungi can then grow further into the
soil helping to also extend the roots of the plants.
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Nematodes:
Soil nematodes are microscopic worms seen in the photo at the
right as being all of the millions of little white lines. They eat
bacteria, fungi, protozoa and other nematodes and release nutrients into the soil
to help plants grow. A few nematodes attack crop roots, cause diseases
and end up harming plants, while a few other predatory nematodes can be
used to fight diseases by spraying them on
the soil. Here, at right, nematodes are feasting on a dead moth.
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Arthropods:
Arthropods are a very different group of oddly
shaped mites, millipedes, beetles, spiders and other creatures, many of
which prey on disease-causing pests and end up helping plants and
helping to make healthier soil. Others help to shape soil
structure, which improves water intake and supplies the soil with oxygen, while others aid in
breaking down dead matter. In the picture at the right you can
see a lion ant waiting for some prey.
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Earthworms:
Earthworms are like underground farmers that create tunnels to
help the water move more quickly and to provide pathways for plant
roots to grow. They also help in soil aggregation, which is
passing little amounts of soil through their bodies to leave it
behind in better condition. You could also think of earthworms
as being little helpers that fertilize and encourage other little
micro-organisms to do the same by decomposing dead organic matter in
the soil.
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Plants and More:
Can you name other organisms that live
in the soil? All kinds of burrowing animals live
underground in the soil such as pocket gophers, shrew, deer
mouse, ground squirrels, white grubs, mole crickets, snakes, frogs,
and even the red fox. You would be surprised to
also find out that some birds even build their homes in the ground.
To the right is a photo of a badger peeking up from his home in the
ground.
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"Every time you take a
step in a mature Oregon forest, your foot is being supported on the
backs of 16,000 invertebrates held up by and average total of 120,000
legs." - Dr. Andrew Moldenke, Oregon State University.
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The tips of small plant
roots move through the soil with a twisting screw-like motion.
Mature trees can have as many as 5 million active root tips.
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A single spade full of
rich garden soil contains more species of organisms than can be found
above ground in the entire Amazon rain forest.
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Although the soil
surface appears solid, air moves freely in and out of it. The
air in the upper 8 inches of a well-drained soil is completely renewed
about every hour.
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The plants growing in a
2-acre wheat field can have more than 30,000 miles of roots, greater
than the circumference of the earth.
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Soil can act as either a
sink or a source of greenhouse gases. An estimated 30 percent of
the carbon dioxide, 70 percent of the methane, and 90 percent of the
nitrous oxide released to the atmosphere each year pass through the
soil.
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It takes about 4,000 to
6,000 pounds of crop residue per year to maintain the content of
organic matter in a soil.
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Of the carbon returned
to the soil as plant residue, about 5 to 15 percent become tied up in
the bodies of organisms and 60 to 75 percent is respired as carbon
dioxide back to the atmosphere. Only 10 to 25 percent is
concerted to humus in the soil.
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Modern farming practices
that minimize soil disturbance (plowing) and return plant residues to
the soil, such as no-till farming and crop rotations, are slowly
rebuilding the Nation's stock of soil and organic matter.
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The wonderful "earthy"
smell of newly plowed ground is believed to result from chemicals
produced by micro-organisms, such as bacteria.
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Even in agricultural soils, more than a
thousand arthropod legs support your every step.
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One cup of soil may hold as many bacteria
as there are people on Earth.
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Bacteria and
actinomycetes are exceedingly tiny. Yet, because of their
tremendous numbers, they make up half the living biomass in some
soils.
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The weight of all
the bacteria in one acre of soil can equal the weight of a cow or
two!!!
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A
teaspoon of farm soil may contain tens of yards of fungi. The
same amount of soil from a coniferous forest may hold tens of miles of
fungi.
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Nematodes are amazingly diverse. Twenty thousand species have
been described, but it is thought that 500,000 species may exist.
Five thousand soil species have been described.
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Earthworms move soil from lower strata up to the surface and move
organic matter from the soil surface to lower layers. Where
earthworms are active, they can turn over the top 6 inches of soil in
ten to twenty years.
PITFALL TRAP (for collecting larger
bugs)
Materials Needed:
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A 1-to-4cup sized container (yogurt
container, soup can, etc.)
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Small shovel
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Magnifying glass (optional)
Steps:
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1. |
Set up
the trap. Pick a spot
to dig where the soil will not be disturbed for a week. Dig a
hole as big as the container. Set the container into the hole
so that the top is exactly even with the soil surface. If it
is higher, the bugs will walk around the edge and not fall in.
Smooth the soil up to the rim of the container. |
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2. |
Collect the bugs.
Leave the trap in place for 1 week, but check it daily to see if you
are collecting anything. |
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3. |
Observe the bugs.
Look at the bugs you collected and notice how they are similar or
different. How many legs do they have. Be careful.
Some can bite! |
Diagram:
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