By Trista L. Pollard
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A rock in one place today may be in another place tomorrow. Thanks to erosion , rock particles produced from weathered rock are moved away from their birth location.
Erosion agents like wind, gravity, glaciers, and water transport weathered rock particles to areas from their parent rock. Water, one of the most important erosion agents, moves weathered rock in many different ways. Ocean waves and currents, streams and runoff, and groundwater are nature's transportation for weathered rocks.
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During the last century, geologists have observed an increase in soil erosion around the world. It is one of the largest environmental problems that the world will encounter during this current century. Weathered rock is eventually changed into finer particles.
These particles are light enough to mix with water, air, and humus. Once this occurs, soil is formed. If we let nature do its job, then the erosion of the soil is a very slow process. Typically the erosion rate of soil is almost equal to the formation rate of soil.
However, once humans and farming practices are involved, the natural erosion rate of soil may be altered.
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Climate and land use can alter the natural balance that exists for soil erosion and formation. As farming and ranching practices have improved over the years, soil erosion has also increased. These practices uproot plants whose roots would normally anchor the soil. Without the anchoring action of plants, soil would be eroded rapidly by wind and water. Animals also increase erosion rates through their overgrazing of grass. They remove important ground cover that helps to slow water runoff. Once the groundcover disappears, the soil becomes more vulnerable to the agents of erosion. So, what is the long-term effect of soil erosion? The long-term effect is a decrease in available fertile land. The first layer to be eroded is the topsoil. Once the topsoil is eroded, the fertility of the soil decreases. As a result, widespread famine may occur.
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Geologists and agricultural scientists have studied two common forms of erosion.
Gullying occurs when furrows or long rows are plowed into land. These furrows, which are plowed along slopes, provide a pathway for water to flow over soil. The furrows become deeper as rain continually washes away the soil. Eventually, gullies form. Once the land becomes covered with gullies, it is not fertile enough to produce crops. Sheet erosion strips away parallel layers of topsoil, exposing the surface of subsoil. Areas that have large amounts of rainfall may experience sheet erosion. The constant rainfall washes away the layers of topsoil. In areas that experience unusually long dry periods, wind may cause sheet erosion. Since the soil does not have the regular moisture from normal rainfall and is very loose, it is easily carried away by wind. The result is clouds of dust and drifting sand which may produce large dust storms. Regardless of the erosion method, the result is a decrease in soil fertility. Once the A horizon is removed, the soil has difficulty supporting vegetation. Remember, the B and C horizons have very little humus. Once the B horizon becomes the topsoil, it is exposed to further erosion from the elements.

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Quick Bit: How is sheet erosion related to the 1930s dust storms that occurred in the Midwestern United States?
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Now that scientists monitor soil erosion and observe its effects, they are studying different methods of soil conservation. Soil conservation has become extremely important since human activities have increased the rate of erosion. In addition to overgrazing and farming practices, construction and mining practices have also increased the rate of erosion. These practices are more prevalent in developing urban areas. As cities, suburbs, and towns become more popular, vegetation is removed to make way for houses, buildings, and roads. Construction companies, mining companies, city planners, and land developers have taken an interest in conserving our soil. Some of these methods include leaving trees and vegetation to hold or anchor the topsoil. When topsoil is stripped away in mountainous regions and deserts, it may take many years before this soil is replenished. This is why soil conservation is extremely important.
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There are certain farming methods that help to protect the soil from erosion.
Contour plowing involves the plowing of soil in curved bands that follow the contours of the land. When the land is plowed according to its shape, then gullying is prevented.
This also prevents groundwater from flowing directly down the slopes. Strip-cropping involves planting crops in alternating rows. The goal of this technique is to plant a crop that exposes the soil to erosion in one band and a cover crop in another band. The cover crop protects the soil from excessive water runoff. The use of strip-cropping has helped to reduce soil erosion by as much as 75%.
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Terracing and crop rotation are two other methods used by farmers to conserve soil. Farmers use terracing for crops that are planted along slopes. They are step-like ridges that are built into the slopes to slow or prevent water runoff. Once these terraces are built, crops can grow without being exposed to increased soil erosion. Crop rotation is used to alternate between soil-exposing and soil-covering crops each year. Farmers plant crops that leave the soil exposed to the agents of erosion one year. Then the next year they plant cover crops to allow the soil to regenerate and to protect it from erosion.
Crop rotation helps to prevent soil erosion at its earliest stages. Remember the gullies?
Well, during crop rotation, gullies that form during one year can have time to fill in with soil during the next year.
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In The Movement of Soil, Part 2 you will learn about the effects of gravity on erosion and how erosion affects some of our major landforms.
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Name _____________________________ Date ___________________
1. True or False: The erosion of soil usually occurs very quickly and very dramatically.
2. Explain how soil erosion in some third world countries may contribute to famine.
4. Why do gullies form? 3. When parallel layers of topsoil are stripped away, this is called ______.
Gullying
Strip-cropping
Sheet erosion
Terracing
5. Why does soil erosion affect soil fertility?
7. Effect: Water does not flow directly down slopes or cause gullying. Instead the water runoff follows the curved bands that have been plowed into the soil.
6. How do human activities affect the erosion rate of soil?
8. Use context clues to define the word prevalent .