Submitted to: Encyclopedia of Soil Science
Publication Type: Book / Chapter
Publication Acceptance Date: 9/30/2005
Publication Date: 5/10/2006
Citation: Dabney, S.M. 2006. Tillage Erosion: Terrace Relationships. Encyclopedia of Soil Science, 2nd Edition, Marcell Dekker, New York, NY. pp. 1752-1754.
Interpretive Summary: Tillage moves soil. The amount of soil moved depends on slope steepness, implement speed and type, and tillage direction. Areas where tillage implements first engage the soil always loose soil, and soil is always deposited where implements leave the field or turn around. Many tillage operations through soil clods from tilled areas into adjacent untilled the field borders. Over time, these clods, together with stones picked from the tilled area and sediment deposited by runoff, coalesce to form terraces. The formation of such terraces may or may not be desirable, but can hardly be avoided if field boundaries are fixed for long periods of time. Such terraces have been recognized for many years and are called “lynchets” by archeologists. This contribution to the Encyclopedia of Soil Science discusses the ways that tillage translocation of soil forms terraces at field boarders, points out ways in which these terraces can be used to advantage for soil and water conservation, and discusses some problems that have been recognized as a result of such terrace development. The article will be valuable to researchers and students interested in understanding and managing agricultural landscapes.
Technical Abstract: All tillage moves soil. Implements drawn by animals or a tractor move soil in the direction of travel and, to a lesser extent, sideways. While a moldboard plow throws soil to only one side, most tillage implements—including tandem disks, chisel plows, harrows, and cultivators—throw soil to both sides. With such implements, a tillage operation along the contour moves some soil uphill, more soil downhill, and still more soil along the contour in the direction of travel. Net soil loss occurs where the tillage tool first engages the soil, as well as on slope convexities. Soil is deposited in depressions, along the upper and lower edges of the tilled area, and at points where the tillage tool is removed from the ground and turned around. With each tillage operation, the field becomes flatter and some soil leaves the tilled zone in the form of clods deposited along field borders. Over time, these clods along with stones removed from the tilled area and sediment deposited by runoff, coalesce to form terraces or lynchets. The formation of such terraces may or may not be desirable, but can hardly be avoided if field boundaries are fixed for long periods of time. This section reviews research into terrace formation by tillage, identifies ways in which these terraces can be advantageous to soil and water conservation, and discusses problems that have been recognized with tillage terraces.