Soil science is the study of soil as a natural resource on the surface of the Earth including soil formation, classification and mapping; physical, chemical, biological, and fertility properties of soils; and these properties in relation to the use and management of soils.
Aridisols are a soil order in USDA soil taxonomy. Aridisols form in an arid or semi-arid climate. Aridisols dominate the deserts and xeric shrublands, which occupy about one third of the Earth's land surface. Aridisols have a very low concentration of organic matter, reflecting the paucity of vegetative production on these dry soils. Water deficiency is the major defining characteristic of Aridisols. Also required is sufficient age to exhibit subsoil weathering and development. Limited leaching in aridisols often results in one or more subsurface soil horizons in which suspended or dissolved minerals have been deposited: silicate clays, sodium, calcium carbonate, gypsum or soluble salts. These subsoil horizons can also be cemented by carbonates, gypsum or silica. Accumulation of salts on the surface can result in salinization.
Oxisols are a soil order in USDA soil taxonomy, best known for their occurrence in tropical rain forest within 25 degrees north and south of the Equator. In the World Reference Base for Soil Resources (WRB), they belong mainly to the ferralsols, but some are plinthosols or nitisols. Some oxisols have been previously classified as laterite soils.
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 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.
Ultisol, commonly known as red clay soil, is one of twelve soil orders in the United States Department of Agriculture soil taxonomy. The word "Ultisol" is derived from "ultimate", because Ultisols were seen as the ultimate product of continuous weathering of minerals in a humid, temperate climate without new soil formation via glaciation. They are defined as mineral soils which contain no calcareous material anywhere within the soil, have less than 10% weatherable minerals in the extreme top layer of soil, and have less than 35% base saturation throughout the soil. Ultisols occur in humid temperate or tropical regions. While the term is usually applied to the red clay soils of the Southern United States, Ultisols are also found in regions of Africa, Asia, Australia and South America.
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 fourth edition 2022. It is edited by a working group of the International Union of Soil Sciences (IUSS).
Terra preta is a type of very dark, fertile anthropogenic soil (anthrosol) found in the Amazon Basin. It is also known as "Amazonian dark earth" or "Indian black earth". In Portuguese its full name is terra preta do índio or terra preta de índio. Terra mulata is lighter or brownish in color.
Gypsisols in the World Reference Base for Soil Resources (WRB) are soils with substantial secondary accumulation of gypsum (CaSO4.2H2O). They are found in the driest parts of the arid climate zone. In the USDA soil taxonomy they are classified as Gypsids (USDA Soil Taxonomy), in the Russian soil classification they are called Desert soils (USSR).
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.
Alkali, or Alkaline, soils are clay soils with high pH, a poor soil structure and a low infiltration capacity. Often they have a hard calcareous layer at 0.5 to 1 metre depth. Alkali soils owe their unfavorable physico-chemical properties mainly to the dominating presence of sodium carbonate, which causes the soil to swell and difficult to clarify/settle. They derive their name from the alkali metal group of elements, to which sodium belongs, and which can induce basicity. Sometimes these soils are also referred to as alkaline sodic soils. Alkaline soils are basic, but not all basic soils are alkaline.
A Calcisol in the World Reference Base for Soil Resources (WRB) is a soil with a substantial secondary accumulation of lime. Calcisols are common in calcareous parent materials and widespread in arid and semi-arid environments. Formerly Calcisols were internationally known as Desert soils and Takyrs.
A Durisol is a Reference Soil Group under the World Reference Base for Soil Resources (WRB) referring to free-draining soils in arid and semi-arid environments that contain grains cemented together by secondary silica (SiO2) in the upper metre of soil, occurring either as concretions (durinodes – duric horizon) or as a continuously cemented layer (duripan – hardpan (Australia) – dorbank (South Africa) – petroduric horizon). The name is derived from Latin durus for hard.
A Technosol in the World Reference Base for Soil Resources is a Reference Soil Group that combines soils whose properties and pedogenesis are dominated by their technical origin. They contain either a significant amount of artefacts, some sort of geotechnical liner, or are sealed by technic hard material. They include soils from wastes, pavements with their underlying unconsolidated materials, soils with geomembranes and constructed soils in human-made materials. Transported natural soil material does not qualify as Technosol and is described with the Transportic qualifier in WRB. Technosols are often referred to as urban or mine soils. They are recognized in the new Russian soil classification system as Technogenic Superficial Formations.
The umbric horizon is a thick, dark coloured, surface soil horizon rich in organic matter. It is identified by its dark colour and structure. Normally it has a pH of less than 5.5 representing a base saturation of less than 50 percent. An indication for soil acidity is a rooting pattern whereby the roots tend to be horizontal.
A fluvisol in the World Reference Base for Soil Resources (WRB) is a genetically young soil in alluvial deposits. Apart from river sediments, they also occur in lacustrine and marine deposits. Fluvisols correlate with fluvents and fluvaquents of the USDA soil taxonomy. The good natural fertility of most fluvisols and their attractive dwelling sites on river levees and higher parts in marine landscapes were recognized in prehistoric times.
Kastanozem is one of the 32 Reference Soil Groups of the World Reference Base for Soil Resources (WRB). These soils are brighter than Chernozems, and are related to the Mollisols in the USDA soil taxonomy. They are rich in humus, and originally covered with early maturing native grasslands vegetation, which produces a characteristic brown surface layer in the first meter in depth. They have a relative high level of exchangeable calcium ions and secondary carbonates starting within 70 cm of the mineral soil surface.
Luvisols are a group of soils, comprising one of the 32 Reference Soil Groups in the international system of soil classification, the World Reference Base for Soil Resources (WRB). They are widespread, especially in temperate climates, and are generally fertile. Luvisols are widely used for agriculture.
A Phaeozem in the World Reference Base for Soil Resources (WRB) is a dark soil with a high base status, but without a secondary carbonates within one metre of the soil surface. Most Phaeozems correlate with the Udolls (Mollisols) of the USDA soil taxonomy.
The Polish Soil Classification is a soil classification system used to describe, classify and organize the knowledge about soils in Poland.
