HISTOSOL

one of the 30 soil groups in the classification system of the Food and Agriculture Organization (FAO). Histosols are low-density, acidic soils with a high proportion of organic material. Formed mainly in cold climates and under waterlogged conditions, they are the most common soil in northern Finland, in western Scotland, in central Canada, and east of the Urals in Russia. They also occur in the bogs and swamps of Ireland, Angola, Bangladesh, and Guyana. Histosols are estimated to cover just over 2.5 percent of the continental land area on Earth, 80 percent of this in cold or boreal climatic zones. Their agricultural use is limited by cold climate, waterlogging, and low fertility. Histosols are technically characterized by organic materials whose cumulative thickness makes up at least half of the upper 80 cm (about 2 feet) of the soil profile. They are identified as fibric if the organic materials show little or no decomposition and as terric if the organic materials are highly decomposed, dark in colour, and not conducive to drainage. They are similar in all respects to the Histosol order of the U.S. Soil Taxonomy. one of the 12 soil orders in the U.S. Soil Taxonomy. Histosols are formed under waterlogged conditions typical of peat bogs, moors, and swamps. Under such conditions, the accumulated tissues of dead plants and animals and their decomposition products are preserved, resulting in soils of high organic content. After drainage for agricultural use (particularly vegetable crops and cranberries), the organic material is prone to oxidation, leading to fire hazards as well as subsidence. Sphagnum and other types of fibrous material are extracted from Histosols for use in horticulture and as fuel. Larger areas of these soils have been managed for flood control, water purification, and wildlife preservation. Histosols occupy less than 2 percent of the nonpolar continental land area on Earth, mostly in Canada, Russia, and Scandinavia. They are characterized by at least 12 to 18 percent organic carbon by mass (depending on the clay content) if occasionally waterlogged or by at least 20 percent organic carbon by mass if never waterlogged. Horizons (layers) similar to those in other orders of the U.S. Soil Taxonomy are not usually observed. Layers are identified as fibrous (or peat) if they contain mostly fibre, hemic (or mucky peat) if they contain mostly decomposing fibre, or sapric (or muck) if they contain little or no undecomposed fibre.