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United States Department of Agriculture

Agricultural Research Service

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Soils & Organisms
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What is soil?


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.  Keep reading for more fun facts about soil.


 

 

Soil can actually be separated into 5 main parts.  They are:
 

Agriculture

Insects
  Crickets, Science4Kids

"Bug" Recipes

Lewis & Clark

Soil & Organisms

Other Fun Websites

  • 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.

  • 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.

  • 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.

  • Sand: Soil that is coarse and drains quickly.  Sand particles measure from about 0.006 millimeters to 2.00 millimeters.

  • Gravel: Visible rock particles, sometimes referred to as pebbles.


 

The "Good" Guys

 

Link to European ginger web page and this is a photo of European ginger doing very well thanks to healthy soil.The vast majority of all organisms living in the soil are "good guys," helping to:

  • Decompose organic matter

  • Release nutrients

  • Create waterways

  • Aid plant growth

  • Aggregate soil

  • Provide us with life-saving antibiotics

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.

 


 

The "Bad" Guys

 

Fungi Fight: C. beticola, the bad guy, is under attack by L. arvalis, the good guy.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.

 


 

Why we need soil?

 

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.

 


 

What lives in soil?

 

Protozoa and BacteriaProtozoa 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. 
 

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.
 

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. 
 

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. 
 

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.
 

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.
 


 

Fun Facts About Soil

  • Photograph of a forest with the caption stating that every time you take step in a mature Oregon forest, your foot is being supported on the backs of 16,000 invertebrates."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.

  • 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.

  • 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.

  • 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.

  • 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.

  • 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.

  • It takes about 4,000 to 6,000 pounds of crop residue per year to maintain the content of organic matter in a soil.

  • 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. 

  • 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.

  • The wonderful "earthy" smell of newly plowed ground is believed to result from chemicals produced by micro-organisms, such as bacteria.

  • Even in agricultural soils, more than a thousand arthropod legs support your every step.

  • One cup of soil may hold as many bacteria as there are people on Earth.

  • Photograph of a cow with the caption stating that the weight of all the bacteria in one acre of soil can equal the weight of a cow or two.Bacteria and actinomycetes are exceedingly tiny.  Yet, because of their tremendous numbers, they make up half the living biomass in some soils.

  • The weight of all the bacteria in one acre of soil can equal the weight of a cow or two!!!

  • 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.

  • 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.

  • 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.


 

Soil Experiment

 

PITFALL TRAP (for collecting larger bugs)

 

Materials Needed:

  • A 1-to-4cup sized container (yogurt container, soup can, etc.)

  • Small shovel

  • Magnifying glass (optional)

Steps:

 

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.

 

2.

Collect the bugs.  Leave the trap in place for 1 week, but check it daily to see if you are collecting anything.

 

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:

Diagram of how to place the small container in the soil so that the top is level with the ground.

 

 

 

 

 

 

 

 

 

 

 

Resources used in compiling this information

 

http://soils.usda.gov/sqi/
http://www.blm.gov/nstc/soil/
http://www.nrcs.usda.gov/
 http://www.ars.usda.gov/Main/docs.htm?docid=16299
http://www.ars.usda.gov/is/kids
 

 


Last Modified: 9/19/2008
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