Water Background II

Where Does the Water Go? Part II
Runoff

Erosion is the movement of soil from one place to another by wind or water. Erosion caused by water is the most wide spread problem. When it rains, the water will either move into the soil, or it will run off, depending on how steeply the land is sloped and whether or not the soil is covered. When soil on a slope is left bare due to drought, crop harvest, cultivation, construction or other soil disturbance, rain falling on that soil can begin moving down hill faster than it can soak in. As the water moves down hill it carries soil with it. The faster the water moves, the more soil is carried. This causes the top soil, the most productive layer, to be carried away.

The top soil is where most of the organic matter is found. This organic matter contributes greatly to the productivity of the soil. Therefore, when top soil is carried away or eroded, the remaining soil is not as productive as before and crops do not grow as well.

Farmers can protect their soil from erosion in several ways. They can build terraces on sloped land which slow down the water and move it off the field in a controlled manner. They also use contour plowing which means that, instead of plowing up and down the slope, they plow across, or at right angles to the slope. This allows water to soak in and not run off. Most farmers use a combination of terraces and contour plowing.

When farmers harvest their crop they leave the stubble, or crop residue, on the surface of the soil. This keeps rain drops from striking the soil directly. When rain drops strike bare soil they can cause the soil to pack and water cannot soak in. The farmer only plows the field when he is ready to plant another crop. Some farmers may not plow the field at all. They just plant the seeds for the new crop directly through the residue left from last year's crop.

Erosion can also be caused by wind blowing across soil. Sandy soils are the most likely to be eroded by wind because they tend to be looser than other types. Farmers in windy areas try to keep their soil covered to prevent wind erosion. They also plant wind breaks on the side of the fields that the wind usually blows. These are trees or shrubs that help keep the wind from blowing directly across the field. The Dust Bowl of the 1920s and 1930s was caused, in part, by wind erosion.

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		Background Information

		Where Does the Water Go? Part II Runoff Erosion is the movement of soil from one place to another by wind or water. Erosion caused by water is the most wide spread problem. When it rains, the water will either move into the soil, or it will run off, depending on how steeply the land is sloped and whether or not the soil is covered. When soil on a slope is left bare due to drought, crop harvest, cultivation, construction or other soil disturbance, rain falling on that soil can begin moving down hill faster than it can soak in. As the water moves down hill it carries soil with it. The faster the water moves, the more soil is carried. This causes the top soil, the most productive layer, to be carried away. The top soil is where most of the organic matter is found. This organic matter contributes greatly to the productivity of the soil. Therefore, when top soil is carried away or eroded, the remaining soil is not as productive as before and crops do not grow as well. Farmers can protect their soil from erosion in several ways. They can build terraces on sloped land which slow down the water and move it off the field in a controlled manner. They also use contour plowing which means that, instead of plowing up and down the slope, they plow across, or at right angles to the slope. This allows water to soak in and not run off. Most farmers use a combination of terraces and contour plowing. When farmers harvest their crop they leave the stubble, or crop residue, on the surface of the soil. This keeps rain drops from striking the soil directly. When rain drops strike bare soil they can cause the soil to pack and water cannot soak in. The farmer only plows the field when he is ready to plant another crop. Some farmers may not plow the field at all. They just plant the seeds for the new crop directly through the residue left from last year's crop. Erosion can also be caused by wind blowing across soil. Sandy soils are the most likely to be eroded by wind because they tend to be looser than other types. Farmers in windy areas try to keep their soil covered to prevent wind erosion. They also plant wind breaks on the side of the fields that the wind usually blows. These are trees or shrubs that help keep the wind from blowing directly across the field. The Dust Bowl of the 1920s and 1930s was caused, in part, by wind erosion.