Glossary of Soil Science Terms - Browse

ice wedge polygon Patterned ground in areas of ice wedges. These polygons are commonly in poorly-drained areas and may be high-centered or low-centered (National Research Council of Canada, 1988).

ice age (not recommended) use Pleistocene.

ice segregation The formation of ice by the migration of pore water to the frozen fringe where it forms into discrete layers or lenses. It commonly ranges in thickness from hairline to more than 10 m and often occurs in alternating layers of ice and soil (National Research Council of Canada, 1988).

ice wedge A massive, generally wedge-shaped body with its apex pointing downward, composed of foliated or vertically banded, commonly white, ice (National Research Council of Canada, 1988).

ice wedge cast A filling of sediment in the space formerly occupied by an ice wedge (National Research Council of Canada, 1988).

ice-contact slope A steep escarpment of predominantly glaciofluvial sediment that was deposited against a wall of glacier ice, marking the position of a relatively static ice-margin; an irregular scarp against which glacier ice once rested (Schoeneberger and Wysocki, personal communication, 2013; Jackson, 1997). Compare head-of-outwash.

ice-margin complex An assemblage of landforms constructed proximal to a relatively static, rapidly wasting continental glacial margin. Constituent landforms can include fosse, head-of-outwash, ice-contact slope, ice-contact delta, kame, kame moraine, kettle, outwash fan, small outwash plain, glacial sluiceway, and small proglacial lake. Moraines, if present, are of limited occurrence (except kame moraines which can be extensive). Glaciofluvial sediments dominate but glaciolacustrine sediments, till, and diamictons can be present in minor amounts (Schoeneberger and Wysocki, personal communication, 2013).

ice-marginal stream A stream drainage along the side or front of a glacier. Relict ice-marginal streams are used to trace the former position of a glacier; also called ice-marginal drainage (Schoeneberger and Wysocki, personal communication, 2013; Jackson, 1997).

ice-pushed ridge An asymmetrical ridge of local, essentially non-glacial material (such as deformed bedrock, with some drift incorporated in it) that has been pressed up by the shearing action of an advancing glacier. It is typically 10 to 60 m high, about 150 to 300 m wide, and as much as 5 km long. Examples are common on the Great Plains where such ridges occur on the sides of escarpments formed of relatively incompetent rocks that face the direction from which the ice moved (Jackson, 1997).

ice-rafting The transportation of rock fragments of all sizes on or within icebergs, ice floes, or other forms of floating ice. Compare dropstone, erratic ( Jackson, 1997).

igneous rock Rock formed by cooling and solidification of magma, and that has not been changed appreciably by weathering since its formation; major varieties include plutonic and volcanic rocks. Examples: andesite, basalt, granite (Schoeneberger and Wysocki, personal communication, 2013). Compare extrusive, intrusive, metamorphic rock.

illite As a general term, refers to either a discrete nonexpansible mica of detrital or authigenic origin or to the micaceous component of interstratified systems, as in illite-smectite. If used to refer to the species, it should meet the following requirements: (i) The micaceous layers ideally are non-expansible; (ii) the octahedral sheet is dioctahedral and aluminous; (iii) the interlayer cation is primarily potassium; and (iv) the composition deviates from that of muscovite in two main ways: (a) A phengitic component is present in which substitution of R₂₊ cations for octahedral Al is balanced by addition of tetrahedral Si beyond the ideal Si/Al ratio of 3:1 for muscovite. This substitution gives the octahedral sheet an overall negative charge of about 0.2 to 0.3 per formula unit.(b) Interlayer vacancies or water molecules amounting to about 0.2 to 0.4 atoms per formula unit are compensated by additional tetrahedral Si cations beyond those required by the phengitic component. Where reference is made to the species illite, a clear statement should be made to that effect in order to avoid confusion with the general usage. (c) In soil taxonomy, the presence of a 1 nm x-ray diffraction peak and greater than or equal to 4% K2O is used to denote the presence of illite.

illuvial horizon A soil layer or horizon in which material carried from an overlying layer has been precipitated from solution or deposited from suspension. The layer of accumulation. Compare eluvial horizon.

illuviation The process of deposition of soil material removed from one horizon to another in the soil; usually from an upper to a lower horizon in the soil profile. Compare eluviation.

illuviation cutan Refer to clay films.

imagery General term for base map or reference map materials.

imbibition Absorption of water into dry soil.

Imhoff cone A graduated volumetric cone used for determining settleable solids in liquid suspensions.

immobile water Stagnant soil solution with neglible water flow but with diffusional exchange of solutes with the mobile water.

immobilization The conversion of an element from the inorganic to the organic form in microbial or plant tissues.

immunofluorescence Fluorescence resulting from a reaction between a substance and a specific antibody that is bound to a fluorescent dye.

imogolite A poorly crystalline aluminosilicate mineral with an ideal composition SiO₂ Al₂O_{3 •} 2.5H₂(+). It appears as threads consisting of assemblies of a tube unit with inner and outer diameters of 1.0 and 2.0 nm, respectively. Imogolite is commonly found in association with allophane and is similar to allophane in chemical properties. Imogolite is mostly found in soils derived from volcanic ash and in weathered pumices and Spodosols.

impact crater (a) [anthropogenic] A generally circular or elliptical depression formed by hypervelocity impact of a projectile or ordinance into earthy or rock material. Compare caldera, crater, meteorite crater; (b) (not recommended–use meteorite crater) A generally circular crater formed by the impact of an interplanetary body (projectile) on a planetary surface ( Jackson, 1997).

impedance The total opposition of a material (e.g., soil, copper wire) to items (e.g., roots, coleoptiles, water, electrons) moving through it.

impeded drainage A condition that hinders the movement of water through soils under the influence of gravity.

impervious Resistant to penetration by fluids or by roots.

in-row subsoiling Refer to tillage, in-row subsoiling.

Inceptisols [soil taxonomy] An order of mineral soils that have one or more pedogenic horizons in which mineral materials other than carbonates or amorphous silica have been altered or removed but not accumulated to a significant degree. Inceptisols commonly have anepipedon and a cambic horizon, but under certain conditions, may have an anthropic, ochric, umbric, histic, plaggen, or mollic epipedon. nceptisols have many kinds of diagnostic horizons. Water is available to plants more than half of the year or more than 90 consecutive days during a warm season (USDA, 1999; Table 2).

incipient ponding (related to erosion terms) when rainfall rate just begins to exceed soil infiltration rate and water starts to pool at the soil surface (before initiating runoff); usually described as time-to-incipient ponding.

inclusion One or more polypedons or parts of polypedons within a delineation of a map unit, not identified by the map unit name; i.e., is not one of the named component soils or named miscellaneous area components. Such soils or areas are either too small to be delineated separately without creating excessive map or legend detail, or occur too erratically to be considered a component, or are not identified by practical mapping methods. Compare component soil; map unit, soil.

incorporation Refer to tillage, incorporation.

independent tetrahedra Silicate type minerals in which no oxygens are shared between silica tetrahedra; silicon-oxygen ration is SiO _4-; example mineral: oliv-₄ine, (Mg, Fe) SiO .

indicator plants Plants characteristically associatedwith specific soil or site conditions, such as soil acidity, alkalinity, wetness, or a chemical element.

indigenous Native to an area.

indurated A very strongly cemented soil horizon. Compare consistence.

infiltrability The flux (or rate) of water infiltration into soil when water at atmospheric pressure is maintained on the atmosphere–soil boundary, with the flow direction being one-dimensionally downward.

infiltration The entry of water into soil.

infiltration capacity Maximum rate at which water soaks into or is absorbed by the soil through the soil surface (Ward and Robinson, 1990). Related term infiltration flux.

infiltration flux (or rate) The volume of water entering a specified cross-sectional area of soil per unit time [L T_-1].

infiltration, cumulative Refer to cumulative infiltration.

infiltrometer A device for measuring the volume or flux (or rate) of liquid (usually water) entry downward into the soil.

infrared (IR) Pertaining to or designating the portion of the electromagnetic spectrum with wavelengths just beyond the red end of the visible spectrum in the wavelength interval from about 0.75 μm to 1 mm.

infrared, middle A term for the midsection of the infrared region of the electromagnetic spectrum with wavelengths from around 2 or 3 μm (varying with the author) to around 25 μm. This is the region commonly referred to when discussing the infrared spectra of chemical compounds, organic or inorganic, and minerals.

infrared, far A term for the longer wavelengths of the infrared region, from 25 μm to 1 mm, the generally accepted shorter wavelength limit of the microwave part of the electromagnetic spectrum. This is severely limited in terrestrial use, as the atmosphere transmits very little radiation between 25 μm and the millimeter regions.

inlet A short, narrow waterway connecting a bay, lagoon, or similar body of water ( Jackson, 1997). Compare tidal inlet.

inner sphere adsorption Adsorption of ions that occurs with the elimination of water of hydration in the space between the adsorbed ion and the surface. The force of retention of ions involves both ionic and covalent bonding. Strong adsorption of anions and cations at variable charge sites in organic matter, oxides, and phyllosilicate edges involves inner sphere adsorption.

inoculate To treat, usually seeds, with microorganisms to create a favorable response. Most often refers to the treatment of legume seeds with Rhizobium or Bradyrhizobium to stimulate dinitrogen fixation, but also refers to the introduction of microbial cultures into sterile growth medium.

inselberg A prominent, isolated, residual knob, hill, or

inset fan (colloquial; southwestern USA) The flood plain of an ephemeral stream that is confined between the fan remnants, ballenas, basin-floor remnants, or closely-opposed fan toeslopes of a basin (Peterson, 1981; Schoeneberger and Wysocki, personal communication, 2013).

integrated drainage A general term for a drainage pattern in which stream systems have developed to the point where all parts of the landscape drain into some part of a stream system, the initial or original surfaces have essentially disappeared, and the region drains to a common base level. Few or no closed drainage systems are present (Schoeneberger and Wysocki, personal communication, 2013).

interbedded Said of beds lying between or alternating with others of different character; especially said of rock material or sediments laid down in sequence between other beds, such as “interbedded” sands and gravels ( Jackson, 1997).

interception Refer to precipitation interception.

interdrumlin The concave to relatively flat bottomed, roughly linear depressions ranging from small saddles or swales to small valleys that separate drumlins or drumlinoid ridges in drumlin fields. Streams, if present, have not had a dominant impact on the formation of the depression (Schoeneberger and Wysocki, personal communication, 2013). Compare drumlin, drumlinoid ridge.

interdrumlin swale Refer to interdrumlin.

interdune The relatively flat surface, whether sandfree or sand-covered, between dunes. Compare interdune valley.

interdune valley A broad interdune area consisting of a low-lying, relatively flat surface commonly found between very large dunes, and which lies in close proximity to the local groundwater table (if present; Jackson, 1997).

interflow Water that infiltrates into the soil and moves laterally through the upper soil horizons until intercepted by a stream channel (Schoeneberger and Wysocki, personal communication, 2013). Refer to throughflow.

interfluve A landform composed of the relatively undissected upland or ridge between two adjacent valleys or drainageways.

interfurrow A low, commonly linear or arcuate ridge of soil mounded between furrows by a plow or other farm equipment and serves as a slightly elevated bedding area for planted crops; also called a row, tillage mound, tillage ridge, tillage row. Interfurrows range fom narrow and peaked (tillage ridge) to broad and flat-topped; size and shape depends upon hopw the elevated areas are made and the crop grown (Schoeneberger and Wysocki, personal communication, 2013). Refer to furrow.

intergrade (a) A taxonomic class at the subgroup level of soil taxonomy having properties typical of the great group of which it is a member and that are characteristic of some class in a higher category (any order, suborder, or great group) and indicates a transition to that kind of soil. (b) A soil that is a member of one such subgroup. Compare extragrade. (c) An expanding type 2:1 layer silicate that has islands of “gibbsite-like”cationic material in the interlayer spaces.

interior valley A large, flat-floored closed depression in a karst area whose drainage is ultimately subsurface and its floor is commonly covered by alluvium. Some interior valleys may become ephemeral lakes during periods of heavy rainfall, when sinking streams that drain them cannot manage the runoff; also called polje (not preferred; Jackson, 1997). Compare karst valley, sinkhole.

interlayer Refer to phyllosilicate mineral terminology.

intermediate position [gilgai] The subsurface location and morphology of the nearly level, transitional area (microslope) between an upwelling morphology (chimney) under a slightly elevated microhigh (i.e., microknoll; mound in Russia) and the bowl morphology of an adjacent microlow (i.e., microbasin, microtrough; depression in Russia) in gilgai or other patterned ground. It can make up a majority of the ground surface area in gilgai (Schoeneberger and Wysocki, personal communication, 2013). Compare chimney, bowl, microslope, gilgai.

intermittent stream A stream, or reach of a stream, that does not flow year-round and that flows only when(i) it receives baseflow solely during wet periods, or (ii) it receives ground-water discharge or protracted contributions from melting snow or other erratic surface and shallow subsurface sources. Compare ephemeral stream.

intermontane basin A generic term for wide structural depressions between mountain ranges that are partly filled with alluvium and called “valleys” in the vernacular. Intermontane basins may be drained internally (bolsons) or externally (semi-bolson; Peterson, 1981).

internal drainage The continuing process in a soil that results in water removal under natural conditions.

internal friction The portion of the shearing strength of a soil indicated by the term σ tan θ in Coulomb’s equation τ = c + σ tan θ, where τ is shear stress, σ is normal stress, c is cohesion, and θ is friction angle. It is usually considered to be due to the interlocking of soil grains and the resistance to sliding between the grains.

interstitial water Water held in the interlayer space of phyllosilicate minerals.

interstratification Mixing of different kinds of silicate layers along the c-direction in a given stack. Interstratification may be regular or random. In regular interstratification, the stacking of the component layers follows a periodic succession. In random interstratification, the distribution of the different layers lacks periodicity and is controlled only by the proportions of the various layers.

interstream divide (a) (not preferred) A synonym for divide. (b) (colloquial in southeastern USA). Broad interstream divide, a wide, relatively level area between incised drainageways; a broad, nearly level “summit” or interfluve (Schoeneberger and Wysocki, personal communication, 2013). Compare broad interstream divide, interfluve.

intertidal (adjective) The coastal environment between mean low tide and mean high tide that alternates between subaerial and subaqueous depending on the tidal cycle (Subaqueous Soils Subcommittee, 2005). Compare subtidal.

intramorainal Said of deposits and phenomena occurring within a lobate curve of a moraine (e.g., within the area occupied by a glacier). Compare extramorainal.

intrazonal soils [soil classification] (obselete not used in soil taxonomy) (a) One of the three orders in soil classification. (b) A soil with more or less well developed soil characteristics that reflect the dominating influence of some local factor of relief, parent material, or age, over the normal effect of climate and vegetation (Baldwin et al., 1938).

intrinsic permeability The property of a porous material that expresses the ease with which gases or liquids flow through it. Often symbolized by k = Kn/ pg, where K is the Darcy hydraulic conductivity, n is the fluid viscosity, p is the fluid density, and g is the acceleration of gravity. Dimensionally, k is an area [L₂]. Compare permeability and soil water.

intrusive Denoting igneous rocks derived from molten matter (magmas) that invaded pre-existing rocks and cooled below the surface of the earth (Hawley and Parsons, 1980). Compare extrusive.

inverse modeling Starting from the results, working backward to determine the input parameters for a model best describing the results (related to modeling terms).

inverse problem Determining the properties of a system from its response to a known stimulus.

inversion Refer to tillage, inversion.

ion activity Single ion activity is calculated by multiplying the concentration by the activity coefficient, usually calculated using the extended Debye–Hückel equation or the Davies equation. Numerically, it approaches the value of the ionic concentration at infinite dilution. Compare activity (chemical).

ion hydration Orientation and bonding of water molecules to the surface of an ion; example:

ion selective electrode An electrochemical sensor, the potential of which (in conjunction with a suitable reference electrode) depends on the logarithm of the activity of a given ion in aqueous solution (e.g., pH, copper, nitrate, and sodium electrodes).

ion selectivity (a) The relative adsorption of an ion by the solid phase in relation to the adsorption of other ions. (b) The relative absorption of an ion by a root in relation to absorption of other ions.

ionic strength A parameter that estimates the interaction between ions in solution. It is calculated as one-half the sum of the products of ionic concentration and the square of ionic charge for all the charged species in a solution. It is needed for calculation of single ion activity.

ions Atoms, groups of atoms, or compounds that are electrically charged as a result of the loss of electrons (cations) or the gain of electrons (anions).

ion–dipole bond The bond resulting from the orientation and attachment of a dipolar molecule to the surface of an ion.

iron oxides Group name for the oxides and hydroxides of iron. Includes the minerals goethite, hematite, lepidocrocite, ferrihydrite, maghemite, and magnetite. Sometimes referred to as “sesquioxides” or “iron hydrous oxides.”

iron pan A hardpan in which iron oxide is the principal cementing agent. Also spelled: ironpan. Compare plinthite, ironstone.

ironstone An in-place concentration of iron oxides that is at least weakly cemented.

irrigable area Refer to irrigation, irrigable area.

irrigation The intentional application of water to the soil, usually for the purpose of crop production. Related terms include:advance time The time it takes the first water applied to a dry irrigation furrow to travel the length of the furrow.alternate set irrigation A method of managing irrigation whereby, at every other irrigation, alternate furrows are irrigated, or sprinklers are placed midway between their locations during the previous irrigation.alternate side irrigation The practice of furrow irrigating one side of a crop row (for row crops or orchards) and then, at about half the irrigation time, irrigating the other side.border dikes Earth ridges built to guide or hold irrigation water within prescribed limits in a field; a small levee.border ditch irrigation A ditch used as a border of an irrigated strip or plot, water being spread from one or both sides of the ditch along its entire length. border-strip irrigation The water is applied at the upper end of a strip with earth borders to confine the water to the strip.