A fragipan is a diagnostic horizon in USDA soil taxonomy. They are altered subsurface soil layers that restrict water flow and root penetration. Fragipans are similar to a duripan in how they affect land-use limitations. In soil descriptions, they are commonly denoted by a Bx or Btx symbol. They often form in loess ground. [1] The first record of fragipans is probably that by John Hardcastle in New Zealand in the 1880s. [2]
The Required Characteristics of a fragipan according to the "Keys to USDA soil taxonomy, tenth edition, 2006" are
What this means in plain English is
The genesis of fragipans is open to considerable debate. Soil scientists often argue over the definition of fragipans and whether or not fragipans exist in certain landscapes. Their formation can be attributed to compacting of soils by glaciers during the last ice age, physical ripening, permafrost processes, or other events that occurred in the pleistocene age. Some fragipans inherit their properties from buried soils called paleosols. It has been proposed that fragipans form by hydroconsolidation, that is the collapse of the soil structure due to loading and wetting. [3]
Loess is a clastic, predominantly silt-sized sediment that is formed by the accumulation of wind-blown dust. Ten percent of the Earth's land area is covered by loess or similar deposits.
Soil structure describes the arrangement of the solid parts of the soil and of the pore space located between them. It is determined by how individual soil granules clump, bind together, and aggregate, resulting in the arrangement of soil pores between them. Soil structure has a major influence on water and air movement, biological activity, root growth and seedling emergence.
USDA soil taxonomy (ST) developed by United States Department of Agriculture and the National Cooperative Soil Survey provides an elaborate classification of soil types according to several parameters and in several levels: Order, Suborder, Great Group, Subgroup, Family, and Series. The classification was originally developed by Guy Donald Smith, former director of the U.S. Department of Agriculture's soil survey investigations.
Mollisols are a soil order in USDA soil taxonomy. Mollisols form in semi-arid to semi-humid areas, typically under a grassland cover. They are most commonly found in the mid-latitudes, namely in North America, mostly east of the Rocky Mountains, in South America in Argentina (Pampas) and Brazil, and in Asia in Mongolia and the Russian Steppes. Their parent material is typically base-rich and calcareous and include limestone, loess, or wind-blown sand. The main processes that lead to the formation of grassland Mollisols are melanisation, decomposition, humification and pedoturbation.
In soil science, agriculture and gardening, hardpan or soil pan is a dense layer of soil, usually found below the uppermost topsoil layer. There are different types of hardpan, all sharing the general characteristic of being a distinct soil layer that is largely impervious to water. Some hardpans are formed by deposits in the soil that fuse and bind the soil particles. These deposits can range from dissolved silica to matrices formed from iron oxides and calcium carbonate. Others are man-made, such as hardpan formed by compaction from repeated plowing, particularly with moldboard plows, or by heavy traffic or pollution.
In soil science, Podzols are the typical soils of coniferous or boreal forests. They are also the typical soils of eucalypt forests and heathlands in southern Australia. In Western Europe, Podzols develop on heathland, which is often a construct of human interference through grazing and burning. In some British moorlands with Podzolic soils, Cambisols are preserved under Bronze Age barrows.
Gelisols are an order in USDA soil taxonomy. They are soils of very cold climates which are defined as containing permafrost within two meters of the soil surface. The word "Gelisol" comes from the Latin gelare meaning "to freeze", a reference to the process of cryoturbation that occurs from the alternating thawing and freezing characteristic of Gelisols.
A soil horizon is a layer parallel to the soil surface, also the decaying matter on it, whose physical, chemical and biological characteristics differ from the layers above and beneath. Horizons are defined in many cases by obvious physical features, mainly colour and texture. These may be described both in absolute terms and in terms relative to the surrounding material, i.e. ‘coarser’ or ‘sandier’ than the horizons above and below.
In USDA soil taxonomy, Entisols are defined as soils that do not show any profile development other than an A horizon. An entisol has no diagnostic horizons, and most are basically unaltered from their parent material, which can be unconsolidated sediment or rock. Entisols are the second most abundant soil order, occupying about 16% of the global ice-free land area.
The World Reference Base for Soil Resources (WRB) is an international soil classification system for naming soils and creating legends for soil maps. The currently valid version is the Update 2015 of the third edition 2014. It is edited by a working group of the International Union of Soil Sciences (IUSS).
Pedocal is a subdivision of the zonal soil order. It is a class of soil which forms in semiarid and arid regions. It is rich in calcium carbonate and has low soil organic matter. With only a thin A horizon (topsoil), and intermittent precipitation calcite, other soluble minerals ordinarily removed by water may build up in the B horizon (subsoil) forming a cemented layer known as caliche. It is not used in the current United States system of soil classification but the term commonly shows up in college geology texts.
The solum in soil science consists of the surface and subsoil layers that have undergone the same soil forming conditions. The base of the solum is the relatively unweathered parent material.
The Canadian System of Soil Classification is more closely related to the American system than any other, but they differ in several ways. The Canadian system is designed to cover only Canadian soils. The Canadian system dispenses with the sub-order hierarchical level. Solonetzic and Gleysolic soils are differentiated at the order level.
George Demas was an American pedologist whose pioneering studies of subaqueous soil contributed to the understanding of soil formation and the expansion of the concept of soil. USDA soil taxonomy was revised as a result.
A duripan is a diagnostic soil horizon of the USDA soil taxonomy that is cemented by illuvial silica into a subsurface hardpan. Similar to a fragipan, Petrocalcic Horizon and petrogypsic horizon, it is firmly cemented and restricts soil management. In soil descriptions, they are most often denoted by the symbol Bqm. The closest equivalent in the Canadian system of soil classification is called a duric horizon, although it does not mean exactly the same thing as a duripan in the United States. They form almost exclusively in arid or Mediterranean climates, and can be as hard as concrete, which makes plowing very difficult or impossible. Soils that include duripans are generally used for grazing or wildlife habitat, and are seldom cultivated.
A petrocalcic horizon is a diagnostic horizon in the USDA soil taxonomy (ST) and in the World Reference Base for Soil Resources (WRB). They are formed when secondary Calcium Carbonate or other carbonates accumulate in the subsoil to the extent that the soil becomes cemented into a hardpan. Petrocalcic horizons are similar to a duripan and a petrogypsic horizon (WRB) in how they affect land-use limitations. They can occur in conjunction with duripans where the conditions are right and there are enough free carbonates in the soil. Calcium Carbonates are found in alkaline soils, which are typical of arid and semiarid climates. A common field test for the presence of carbonates is application of hydrochloric acid to the soil, which indicates by fizzing and bubbling the presence of calcium carbonates.
The soil biomantle can be described and defined in several ways. Most simply, the soil biomantle is the organic-rich bioturbated upper part of the soil, including the topsoil where most biota live, reproduce, die, and become assimilated. The biomantle is thus the upper zone of soil that is predominantly a product of organic activity and the area where bioturbation is a dominant process. Soil bioturbation consists predominantly of three subsets: faunalturbation, floralturbation, and fungiturbation. All three processes promote soil parent material destratification, mixing, and often particle size sorting, leading with other processes to the formation of soil and its horizons. While the general term bioturbation refers mainly to these three mixing processes, unless otherwise specified it is commonly used as a synonym to faunalturbation.
The permafrost carbon cycle is a sub-cycle of the larger global carbon cycle. Permafrost is defined as subsurface material that remains below 0o C for at least two consecutive years. Because permafrost soils remain frozen for long periods of time, they store large amounts of carbon and other nutrients within their frozen framework during that time. Permafrost represents a large carbon reservoir that is seldom considered when determining global terrestrial carbon reservoirs. Recent and ongoing scientific research however, is changing this view.
Calcids are a soil suborder in the USDA soil taxonomy. They are aridisols that have accumulated high levels of residual or dryfall calcium carbonate.
Anthroposols are soils which have been profoundly modified or constructed by humans. They typically have one or more of their natural soil horizons modified, removed or replaced. The word anthroposol is derived from the Greek words anthropos, meaning man and genes meaning caused. Anthroposols are typically found on industrial, commercial, urban and resources extraction sites as well as throughout transportation, fuel and power corridors.