Histosols

Histosols (from Greek histos, "tissue") are soils that are composed mainly of organic materials. They contain at least 20-30% organic matter by weight and are more than 40 cm thick. Bulk densities are quite low, often less than 0.3 g cm3. They are often referred to as peats and mucks and have physical properties that restrict their use for engineering purposes. These include low weight-bearing capacity and subsidence when drained. Histosols are divided into five suborders: Folists, Wassists, Fibrists, Saprists and Hemists.

Most Histosols form in settings such as wetlands where restricted drainage inhibits the decomposition of plant and animal remains, allowing these organic materials to accumulate over time. As a result, Histosols are ecologically important because of the large quantities of carbon they contain. These soils occupy approximately 1.2% of the ice-free land area globally and approximately 1.6% of the U.S.

Histosols layers
Histosols are organic soil materials that either: (1) are saturated with water for at least 30 days per year unless drained and have a minimum thickness of 40-60 cm depending on fiber content; or (2) constitute at least 2/3 of the total soil thickness to a root-restrictive layer. (USDA-NRCS)

Folists

Histosols that are not saturated with water for long periods of time during the year

Fibrists

Histosols that are primarily made up of only slightly decomposed organic materials, often called peat

Saprists

Histosols that are primarily made up of highly decomposed organic materials, often called muck

Histosol land use

Histosols, organic soils formed from accumulated partially decomposed plant materials