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Subsoil

From Wikipedia, the free encyclopedia
Subsoil layer

Subsoil is the layer of soil under the topsoil on the surface of the ground. Like topsoil, it is composed of a variable mixture of small particles such as sand, silt and clay, but with a much lower percentage of organic matter and humus, The subsoil is also called B Horizon and normally has less organic matter than topsoil, so its colour is mainly derived from iron oxides. Iron oxides and clay minerals accumulate as a result of weathering. In soil, where substances move down from the topsoil, this is the layer where they accumulate. The process of accumulation of clay minerals, iron, aluminum, and organic compounds, is referred to as illuviation. The B horizon has generally a soil structure.

Whereas the topsoil tends to be the site containing the greatest physical, chemical, and biological activity, the subsoil is the region of deposition where iron oxide, clay particles, and small amounts of organic material reaching from the topsoil can be found. It is also less weathered than the topsoil. Due to human activity, the topsoil and subsoil in many environments has been mixed together. Below the subsoil is the soil base (or C horizon).

Clay-based subsoil has been the primary source of material for adobe, cob, rammed earth, wattle and daub, and other earthen construction methods for millennia. Coarse sand, the other ingredient in most of these materials, is also found in subsoil.

Although by no means sterile, subsoil is relatively barren in terms of soil organisms compared to humus-rich topsoil.

See also

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Sources

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  • Håkansson, Inge; Reeder, Randall C. (March 1994). "Subsoil compaction by vehicles with high axle load—extent, persistence and crop response". Soil and Tillage Research. 29 (2–3): 277–304. doi:10.1016/0167-1987(94)90065-5. (subscription required)
  • Adams, Fred; . Moore, B. L (January 1983). "Chemical Factors Affecting Root Growth in Subsoil Horizons of Coastal Plain Soils". Vol. 47 No. 1. Soil Science Society of America Journal. pp. 99–102. Retrieved October 11, 2012. (subscription required)