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.
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.
- 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)
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