Histosol

In both the FAO soil classification and the USA soil taxonomy, a Histosol is a soil comprised primarily of organic materials. They are defined as containing at least 20 percent organic material to a depth of 40 centimetres. Typically, Histosols have very low bulk density and are poorly drained because the organic matter holds water very well. Most are acidic and many are very deficient in major plant nutrients which are washed away in the consistently moist soil.
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Wet organic soils, such as peats and mucks.