peat, soil material consisting of partially decomposed organic matter, found mainly in swamps and bogs in various parts of the northern temperate zone but also in some semitropical and tropical regions. Peat is formed by the slow decay of successive layers of aquatic and semiaquatic plants, e.g., sedges, reeds, rushes, and mosses, and is the earliest stage of transition from compressed plant growth to the formation of coal. One of the principal types of peat in northern regions is moss peat, derived primarily from sphagnum moss; it is used in agriculture as poultry and stable litters as well as a mulch, a soil conditioner, and an acidifying agent; it is also used in industry as an insulating material. Another type of peat is fuel peat, which has been most widely used in regions where coal and wood are scarce, e.g., Scandinavia, Ireland, Scotland, and parts of Russia. The burning of peat, however, produces greater carbon emissions than coal.

The most extensive peat deposits are found in Canada and Russia, with significant peatlands also in N Europe and NE China. A large peatland found in 2014 in N Congo-Brazzaville and neighboring Congo-Kinshasa has since been determined to extend over some 55,000 sq mi (140,000 sq km). Other tropical peatlands are found in Indonesia and parts of the Amazon region. Large deposits of peat in the United States are found in Alaska, Florida, Louisana, Michigan, and California. The formation of peat acts as a carbon sink, removing carbon dioxide from the atmosphere, but that carbon dioxide is released when peatlands dry out naturally or are drained, and when peat is burned.

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