Soil Erosion

Factors Affecting Soil erosion

Factors affecting soil erosion include climate, soil properties, slope gradient and length, vegetation, and soil management practices. Drier climates mean less vegetation and less plant cover to protect the ground surface from raindrop impact and from the flow of water over the surface. Drier soils are also more susceptible to wind erosion than moist soils due to lower particle cohesion. Soils with low clay content and a high content of fine to medium sand tend to be most susceptible to erosion from water and wind. Soils with high clay content tend to be less susceptible due to their ability to form stable aggregates that are resistant to erosive forces. Steeper slopes mean that runoff flows more [Page 2584]rapidly, and with more erosive force, while longer slopes provide greater distances for runoff to build up speed. Vegetation reduces soil erosion by providing cover to protect soil surfaces against erosive forces, while organic matter from the breakdown of plant residues helps produce stable soil aggregates. Management practices that build up soil organic matter, increase groundcover, and incorporate other methods of soil conservation help lower erosion risks.

Severe soil erosion in a wheat field near Washington State University

Source: Jack Dykinga/Agricultural Research Service, U.S. Department of Agriculture.

History of Soil erosion

Since humans began growing crops and modifying the landscape, accelerated soil erosion has been a major problem facing humankind. Soil erosion has been among the culprits blamed for the decline of civilizations such as the Mesopotamian civilization, the Classical Mayan civilization, and the Roman Empire. Soil erosion is also linked to the mass exodus of migrants in the 1930s from the western Great Plains when drying conditions combined with severe wind erosion set off the series of events that turned the region into a “Dust Bowl.”

Humans have long been aware of the consequences of accelerated soil erosion caused by their activities. Passages in the Old Testament mention threats of streams drying up, while the Greek philosopher Plato referred to the relationship between flood damage and deforestation, and the Roman writer Virgil advocated what amounted to conservation farming. Many early civilizations were not overly concerned with erosion's impacts because most of these civilizations had developed on irrigated alluvial plains, and thus, they counted on erosion in the headwaters of rivers such as the Nile, the Tigris, and the Euphrates to provide sediments to renew soil fertility. By the late 18th century, however, more observers began to notice the consequences of accelerated erosion, partly due to the increased impacts of humans on the landscape as populations began to grow at unprecedented rates. In 1818, James Madison lectured on the evils of poor land management. In 1864, George Perkins Marsh wrote about the impacts of forest clearance on river sedimentation and flooding in New England and the Mediterranean Basin.

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