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Soil Erosion


Soil Erosion Types

Erosion is the wearing away of the earth's surface by the forces of water and wind. It is a natural process, which can have striking results, such as the Grand Canyon or the Dakota Badlands, but most often is a slow, less dramatic process. A large portion of the world's population gets its food supply from soils formed as a result of natural geologic erosion.
When the natural landscape is disturbed by activities of humans such as tillage, timber harvesting, urban development, road construction, or overgrazing, erosion can become accelerated and destructive. Healthy productive soil is lost and sediments damage or clog water bodies, rivers, streams and reservoirs.

Erosion is divided into two main categories, water and wind.

Water erosion has several forms, including:

  • Sheet - uniform removal of soil without the development of conspicuous water channels
  • Rill - removal of soil through the cutting of numerous small but conspicuous water channels or tiny rivulets
  • Gully - removal of soil through the formation of relatively large channels or gullies cut into the soil by concentration of runoff; gullies can be "classic" or "ephemeral"

Wind erosion results in soil movement by three processes:

  • Saltation - fine and medium sand-sized particles are lifted a short distance into the air, dislodging more soil as they fall back to the ground
  • Suspension - very fine soil particles are lifted from the surface by the impact of saltation and carried high into the air, remaining suspended in air for long distances
  • Surface Creep - the movement of large soil particles along the surface of the soil after being loosened by the impact of saltating particles

1997 NRI Soil Erosion Results

The NRI estimates sheet and rill erosion together using the Universal Soil Loss Equation (USLE). The Revised Universal Soil Loss Equation (RUSLE) was not used in the 1997 NRI. RUSLE was not available for previous inventories, therefore the use of USLE was continued to preserve the trending capacity of the NRI database. Wind erosion is estimated using the Wind Erosion Equation (WEQ).

Erosion estimates are based on an annual average for the entire crop rotation. WEQ and USLE estimate erosion caused by distinct processes which are not mutually exclusive in nature. Results from WEQ and USLE can not be added together.

These erosion prediction models are used to estimate water and wind erosion on several land uses. The land use with the most severe erosion problem is Cultivated Cropland. Cultivated Cropland does not include land in the Conservation Reserve Program (CRP).

Erosion equations provide an estimate of soil movement. Not all eroded soil is removed or lost from the field or deposited into water bodies.

Classic and ephemeral gully erosion and streambank erosion are not included in NRI erosion estimates, but may cause significant soil loss in some areas. Information on USLE and WEQ is found in Ag Handbook 537 and the National Agronomy Manual.

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