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How great can soil be? After all, we walk all over it. |
 Soil |
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Soil, like the air we breathe and the water we drink, is vitally important to maintaining life. And like those other resources, soil must be protected if we are to have an adequate quanity of fertile soils on which we can grow crops.
What is soil? The simplest answer is soil is dirt. At least, that is what we call it when it's on our clothes or on a freshly mopped floor in your house. But soil is a lot more than dirt.
While soil is found all over the planet, not all soil will grow food for humans or animals in any quantity. Many areas of the world are too hot or cold; others are too wet or dry. In some places, the soil is too thin and rocky.
If you or your teacher have done the activity with the apple (Earth's Valuable Soil), you'll see that only about 1/32 of the soil in the world can be used to grow crops, and less than 1 percent of Alaska's vast acreage is used to grow food. An alarming amount of cropland is being lost to urbanization -- for example, a shopping mall or factory going on land that was once a farmer's field. Many states have laws protecting farmland, but farmland in the US and other parts of the world continues to dwindle. Other land is lost because of salinity. That's when the salts that natural occur in soil and water build up to dangerous levels because of excessive use of irrigation water.
So why do we still have lots of food? Because productivity -- the amount of food or fiber each acre can produce -- continues to increase. Today's farmers know much more about control erosion and preserving the fertility of their soil than farmers did nearly 70 years ago when a great drought caused what is called The Dust Bowl on the Great Plains. Since then, the federal government has had an agency, now called the Natural Resources Conservation Service, to help farmers and other land owners keep their soil from eroding. But we are still losing soil. In the 1990s, an estimated 2 billion tons of topsoil was lost to erosion.
Is Alaska losing soil, too? Yes. Because there is less farming, the tons lost seem small by comparison. But wind and water erosion moves soil away here, too.
Alaska has some unique soils because of the permafrost in some areas of Interior and Arctic Alaska. Permafrost -- areas where the soil never completely thaws -- is more than 2,000 feet deep on the North Slope. All soils have names, and the soils are grouped into soil orders. Alaska has seven of the 12 soil orders. Alaska's most common soil order is Gelisols. Those are the soils with permafrost.
Other Alaska soils:
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Andisols, formed from volcanic ash |
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Entisols, new soils with little development |
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Histosols, dominated by organic soil material and found in wet areas |
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Inceptisols, light-colored or dark-colored soils over a developed horizon |
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Mollisols, dark rich fertile surface layer. These are the least extensive soils in Alaska. |
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Spodosols, formed under forest vegetation, with a light gray-colored horizon over a dark reddish-brown horizon. |
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| So what's a soil horizon? |
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Soil scientists break soil into layers, called horizons. On many soils these layers are easy to see and form what is called a soil profile. To see a soil profile, soil scientists bore holes in the earth with a metal tube. The soil they pull from the ground stays in its layers and forms the profile. In its simplest form, the soil profile looks like this. The leaves, bugs and other debris form a humus layer. Layer A is the topsoil—the darkest, richest part of most soils. Here is where roots of plants, burrowing bugs and worms and other creatures live. The next layer is Layer B or the B Horizon. It is also called the subsoil. This layer is usually darker near the top and lighter near the bottom. As the organic matter of the humus works its way into the soil, the nutrients flow through—leach—from the topsoil into the subsoil, unless a plant uses the nutrients. Sometimes the B layer has streaks or spots because of mineral deposits or drainage patterns. The lower layer, the C Horizon, is the parent matterial. This is weathered rock that has not broken down into soil.
Want to make your own soil profile and eat it, too? Click here for instructions. |
| How do soils form? |
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Soil is formed when bits of rock wear off. In Alaska, common parent materials of soils are the following:
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Volcanic ash |
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Alluvium (left by flowing water) |
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Colluvium (material that collects at the foot of a steep slope) |
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Igneous, metamorphic and sedimentary rocks-- glacial material |
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Eolian material (windborne) |
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Loess (windborne in glacial areas) |
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Organic material |
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| Why do we need to conserve soil? |
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Soils are regenerating themselves all the time. When a river wears away a rock, soil is formed. When wind chips away a mountain, soils are formed. But it can take thousands of years to make even one ton of soil. And if 3 tons per acre of soil are lost each year, well, you do the math.
To learn more about soil, visit the USDA Natural Resources Conservation Services Alaska. For other great sites about soil, go to Ag Links. |
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