Physical properties


Soil with subsurface accumulation of low activity clay minerals and low base saturation (from the Latin, acris, meaning very acid). An Acrisol is a highly weathered soil occurring in warm temperate regions and the wetter parts of the tropics and subtropics. Acrisols have poor chemical properties, low levels of plant nutrients, high levels of aluminium and high susceptibility to erosion. These conditions are strong limitations for agricultural use.


Acid soil with a bleached horizon penetrating a clay accumulation horizon (from the Latin, albus, meaning white and eluere, meaning to wash out). Albeluvisols have an accumulation of clay in the subsoil with an irregular or broken upper boundary and deep penetrations or ‘tonguing’ of bleached soil material into the illuviation horizon. The typical albeluvic tongues are generally the result of freeze-thaw processes in periglacial conditions and often show a polygonal network in horizontal cuts.


Young soil developed from highly weatherable volcanic deposits (from the Japanese, an, meaning black, and do, meaning soil). Most Andosols are formed from volcanic ejecta (ash, pumice, cinder) and related parent materials. The rapid chemical weathering of porous, permeable, fine-grained mineral material, in the presence of organic matter, generally results in the rapid development of soil profiles. The dark topsoil is generally different in colour from subsoil.


Anthrosols is a type of soil that has been formed or heavily modified due to long-term human activity, such as from irrigation, addition of organic waste or wet-field cultivation used to create paddy fields. Such soils can be formed from any parent soil, and are commonly found in areas where agriculture has been practised for centuries. Anthrosols can be found worldwide, though they tend to have different soil horizons in different regions.  For example, in northwestern Europe Anthrosols commonly have plaggic or terric horizons, and together they cover some 500,000 hectares. 


Easily erodable sandy soil with slow weathering rate, low water and nutrient holding capacity and low base saturation (from the Latin, arena, meaning sand). Arenosols have a coarse texture to a depth of one metre or to a hard layer. Soil formation is limited by low weathering rate and frequent erosion of the surface. If vegetation has not developed, shifting sands dominate. Accumulation of organic matter in the top horizon and/or lamellae of clay, and/or humus and iron complexes, mark periods of stability. Arenosols are amongst the most extensive soil types in the world.


Soil with significant accumulation of secondary calcium carbonates, generally developed in dry areas (from the Latin, calcarius, meaning calcareous or lime-rich). Calcisols have substantial movement and accumulation of calcium-carbonate within the soil profile. The precipitation may occur as pseudomycelium (root channels filled with fine calcite), nodules or even in continuous layers of soft or hard lime (calcrete). Calcisols are common on calcareous parent material in regions with distinct dry seasons, as well as in dry areas where carbonate-rich groundwater comes near the surface.


Soil that is only moderately developed on account of limited age or rejuvenation of the soil material (from the Latin cambiare meaning to change). A Cambisol is a young soil. Pedogenic processes are evident from colour development and/or structure formation below the surface horizon. Cambisols occur in a wide variety of environments around the world and under all many kinds of vegetation.


Soil with a deep, dark surface horizon that is rich in organic matter and secondary calcium carbonate concentrations in the deeper horizons (from the Russian for chern, black, and zemlja, earth). Soil having a very dark brown or blackish surface horizon with a significant accumulation of organic matter, a high pH and having calcium carbonate deposits within 50 cm of the lower limit of the humus rich horizon. Chernozems show high biological activity and are typically found in the long-grass steppe regions of the world. Chernozems are amongst the most productive soil types in the world.


Soil of cold areas with permafrost within a depth of 1m from the surface (from the Greek kraios, meaning cold or ice). Cryosols develop in arctic and mountainous regions where permanently frozen subsoil or permafrost is found. In this type of soil, water occurs primarily in the form of ice and cryogenic processes – such as ‘freeze-thaw’ sequences, ‘cryo-turbation’, ‘frost heave’, ‘cryogenic sorting’, ‘thermal cracking’ and ‘ice segregation’ are the dominant soil forming processes. These processes result in distorted horizons and patterned ground.


Durisols contain cemented secondary silica (SiO2) in the upper one meter of the soil. Their typical feature is the presence of a hard-cemented layer identified as the “duripan phase”. In the Mediterranean, they occur on level and slightly sloping alluvial plains, terraces and gently sloping piedmont plains mainly in Jordan, Syria, Morocco, Tunisia, and Algeria. They are often found in association with Gypsisols, Calcisols, Solonchaks, Solonetz, Vertisols, Arenosols, and Cambisols.


Young soil in alluvial (floodplain), lacustrine (lake) and marine deposits (from the Latin, fluvius, meaning river). Fluvisols are common in periodically flooded areas such as alluvial plains, river fans, valleys and tidal marshes, on all continents and in all climate zones. Fluvisols show layering of the sediments rather than pedogenic horizons. Their characteristics and fertility depend on the nature and sequence of the sediments and length of periods of soil formation after or between flood events.


A Glacier is a persistent body of dense ice that is constantly moving under its own weight. On Earth, 99% of glacial ice is contained within vast ice sheets in the polar regions, but glaciers may be found in mountain ranges on every continent except Australia, and on a few high-latitude oceanic islands.


Soil saturated by groundwater near the surface for long periods (from the Russian, gley, meaning ‘mucky mass’) Gleysols occur mainly in lowland areas where the groundwater comes close to the surface and the soil is saturated with groundwater for long periods of time. Conditioned by excessive wetness at shallow depth, this type of soil develops gleyic colour patterns made up of reddish, brownish or yellowish colours on ped surfaces or in the upper soil layers, in combination with greyish/bluish colours inside the peds or deeper in the soil profile. Gleysols are generally not well drained and need intensive management before they can be used Not the characteristic red and bluish/grey mottling and the presence of water in the profile pit.


Gypsisols are characterised by the substantial accumulation of secondary gypsum (CaSO4). The natural vegetation is made of xerophytic plants (cacti are xerophytic shrubs) and ephemeral grasses. The largest concentration of Gypsisols in the Mediterranean occurs in the Libyan Desert, Jordan, Syria, parts of Central Anatolia and Cyprus. The agricultural use of Gypsisols depends on the gypsum content in the upper topsoil layer. If the gypsum content is low they can be used for production of small grains, cotton, and forage crops. In the Gypsisols of alluvial plains, irrigation and drainage are necessary for the cultivation of crops, fruit trees, and grapes. However large areas are used only for extensive grazing.


Dark soil with high accumulation of partially decomposed organic matter generally developed in wet or cold conditions (from the Greek, histos, meaning tissue). Histosols are composed mainly of organic soil material. During development, the organic matter production exceeds the rate of decomposition. The decomposition is retarded mainly by low temperatures or anerobic (low oxygen) conditions which result in high accu- mulations of partially decomposed organic matter.


Soil with surface horizon rich in organic matter and with calcium carbonate or gypsum accumulation in subsurface horizons (from the Latin castanea, chestnut, and the Russian, zemlja, meaning earth or land). Kastanozems have a deep, dark coloured surface horizon with a significant accumulation of organic matter, high pH and an accumulation of calcium carbonate within 100 cm of the soil surface.


Shallow soil over hard rock or gravelly material (from the Greek, leptos, meaning thin). Leptosols are shallow over hard rock and comprise of very gravelly or highly calcareous material. They are found mainly in mountainous regions and in areas where the soil has been eroded to the extent that hard rock comes near to the surface. Because of limited pedogenic development, Leptosols do not have much structure.


Lixisols develop on old landscapes in a tropical climate with a pronounced dry season. Their age and mineralogy have led to low levels of plant nutrients and a high erodibility, making agriculture possible only with frequent fertilizer applications, minimum tillage, and careful erosion control. Perennial crops are thus more suitable for these soils than root or tuber crops. They occupy just under 3.5 percent of the continental land area on Earth, mainly in east- central Brazil, India, and West Africa.


Soil with a subsurface horizon of high activity clay accumulation and high base saturation (from the Latin, luere, meaning to wash). Luvisols show marked textural differences within the profile. The surface horizon is depleted in clay while the subsurface ‘argic’ horizon has accumulated clay.


Occupying around 2% of the Earth’s surface, Nitisols are found mainly in eastern Africa, coastal India, South America, and tropical islands (Cuba, Java, and the Philippines). They are perhaps the most fertile of the tropical soil types (EM).


Soil with a deep, dark surface horizon that is rich in organic matter without secondary calcium carbonate concentrations within 1m (from the Greek, phaios, meaning dusk and the Russian, zemlja, meaning earth or land). Phaeozems are found in wet steppe (prairie) regions and are much like Chernozems and Kastanozems but more intensively leached in wet seasons. Consequently, they have a dark, humus-rich surface horizon and have no secondary carbonates in the upper metre of soil.


Planosols is a soil with a light-coloured, coarse- textured, surface horizon that shows signs of periodic water stagnation and abruptly overlies a dense, slowly permeable subsoil with significantly more clay than the surface horizon. These soils are typically in seasonally waterlogged flat lands. They occur mainly in subtropical and temperate, semi-arid and subhumid regions.


Plinthosols form under a variety of climatic and topographic conditions. They are defined by a subsurface layer containing an iron-rich mixture of clay minerals (chiefly kaolinite) and silica that hardens on exposure into ironstone concretions known as plinthite. The impenetrability of the hardened plinthite layer, as well as the fluctuating water table that produces it, restrict the use of these soils to grazing or forestry, although the hardened plinthite has value as subgrade material for roads or even as iron ore (the iron oxide content can be as high as 80% by mass). Plinthosols occupy about 0.5% of the total continental land area on Earth, mainly in Brazil and West Africa.


Acid soil with a bleached horizon underlain by an accumulation of organic matter, aluminium and iron (from the Russian, pod, meaning under, and zola, meaning ash). Under acidic conditions aluminium, iron and organic compounds migrate from the surface soil down to the B-horizon with percolating rainwater. The humus complexes deposit in an accumulation (spodic) horizon while the overlying soil is left behind as a strongly bleached albic horizon. Most Podzols develop in humid, well drained areas, particularly, in the Boreal and Temperate Zones.


Soils with limited development (from Greek, rhegos, meaning blanket). A Regosol is a very weakly developed mineral soil in unconsolidated materials with only a limited surface horizon having formed. Limiting factors for soil development range from low soil temperatures, prolonged dryness, characteristics of the parent material or erosion. Regosols are extensive in eroding lands, in particular, in arid and semi-arid areas and in mountainous regions.


Strongly saline soil (from the Russian, sol, meaning salt and chak, meaning salty area). Solonchaks are a strongly saline soil type with high concentration of soluble salts.  They occur where saline groundwater comes near to the surface or where the evapo-transpiration is considerably higher than precipitation, at least during a large part of the year.Salts dissolved in the soil moisture remain behind after evaporation of the water and accumulate at or near the surface.  Their morphology, characteristics and limitations to plant growth depend on the amount, depth and composition of the salts.


Soil with subsurface horizon of clay accumulation and high sodium content (from the Russian, sol, meaning salt and etz, meaning strongly expressed). Strongly alkaline soil with a subsurface horizon of clay minerals, strong columnar structure and high proportion of adsorbed sodium and/or magnesium ions. Solonetz are normally associated with flat lands in a climate with hot, dry summers or with former coastal deposits that contain a high proportion of salt. Solonetz soil occurs mainly in the Ukraine, Russia, Kazakhstan, Hungary, Bulgaria and Romania.


Soil with dark, acid, surface horizon rich in organic matter (from the Latin, umbra, meaning shade). Umbrisols generally develop in cool and humid climates, where precipitation considerably exceeds evapotranspiration.


Seasonally cracking soil, rich in swelling clays (from the Latin, vertere, to turn). Vertisols are rich in swelling clay minerals and occur primarily in level landscapes under climates with pronounced dry and wet seasons. Vertisols shrink and swell upon drying and wetting. Deep wide cracks form when the soil dries out and swelling in the wet season and creates polished and grooved ped surfaces (slickensides) or wedge-shaped or parallel-sided aggregates in the subsurface vertic horizon.


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