Glossary of Soil Science Terms - Browse
E horizon Refer to soil horizon and Appendix II.
earth hummock A type of hummock consisting predominantly of a core of silty and clayey mineral soil and showing evidence of cryoturbation. Earth hummocks are a type of nonsorted circle commonly found in tundra or permafrost (typically 10-50 cm height; 20-300 cm diameter). Compare turf hummock, hummock [patterned ground], non-sorted circle, patterned ground (National Research Council of Canada, 1988).
earth spread [mass movement] The process, associated sediments (earth spread deposit) or resultant landforms characterized by a very rapid type of spread dominated by lateral movement in a soil mass resulting from liquefaction or plastic flow of underlying materials that may be extruded out between intact units. Refer to debris spread, rock spread, landslide (Schoeneberger and Wysocki, personal communication, 2013; Varnes, 1978).
earth topple [mass movement] The process, associated sediments (earth topple deposit) or resultant landform characterized by a localized, very rapid type of topple in which large blocks of soil material literally fall over, rotating outward over a low pivot point; sediments <2 mm predominate. Portions of the original material may remain intact, although reoriented, within the resulting deposit (Schoeneberger and Wysocki, personal communication, 2013). Compare debris topple, rock topple, landslide.
earth dike (not preferred) Use levee [stream)].
earth fall (not preferred) Use soil fall.
earth pillar A tall, conical column of unconsolidated to semi-consolidated earth materials (e.g., clay till, or landslide debris) produced by differential erosion and usually capped by a flat, hard rock fragment that shields the underlying, softer material from erosion. It can measure up to 20 m in height, and its diameter is a function of the width of the protective boulder ( Jackson, 1997). Compare hoodoo.
earthflow [mass movement] The process, associated sediments (earthflow deposit) or resultant landforms characterized by slow to rapid types of flow dominated by downslope movement of soil, rock, and mud (more than 50% of the particles are <2 mm), and whether saturated or comparatively dry, behaves as a viscous fluid when moving. Compare debris flow (coarser, less fluid), mudflow (finer, more fluid; Schoeneberger and Wysocki, personal communication, 2013).
EC Refer to electrical conductivity.
ECe The electrical conductance of an extract from a soil saturated with distilled water, normally expressed in units of siemens or decisiemens per meter at 25°C.
ecofallow Refer to tillage, chemical fallow.
economic rate The application rate of material, usually fertilizer, that gives the highest economic returns for the crop produced.
ectomycorrhiza(e) A mycorrhizal association in which the fungal mycelia extend inward, between root cortical cells, to form a network (“Hartig net”) and outward into the surrounding soil. Usually the fungal hyphae also form a mantle on the surface of the roots.
edaphic (a) Of or pertaining to the soil. (b) Resulting from or influenced by factors inherent in the soil or other substrate, rather than by climatic factors.
edaphology The science that deals with the influence of soils on living things; particularly plants, including humankind’s use of land for plant growth.
edge site The edge location on a layer silicate particle that is a source of pH dependent charge.
effective precipitation That portion of the total rainfall precipitation which becomes available for plant growth.
effective cation exchange capacity (ECEC) Refer to cation exchange capacity (CEC).
effective porosity That portion of the total porosity available for fluid flow.
effective stress The stress transmitted through a soil by intergranular pressures.
EH The potential that is generated between an oxidation or reduction half-reaction and the standard hydrogen electrode (0.0 v at pH = 0). In soils it is the potential created by oxidation-reduction reactions that take place on the surface of a platinum electrode measured against a reference electrode minus the EH of the reference electrode . This is a measure of the oxidation-reduction potential of electrode reactive components in the soil. Compare pe.
elastic Capable of rebounding to an original shape when deformed under moderate pressure.
electrical conductivity (EC) (a) Conductivity of electricity through water or an extract of soil. Commonly used to estimate the soluble salt content in solution. (b) The ability of the soil to conduct electricity.
electrical potential Work required to move a unit positive charge from the bulk solution to a point at a known distance from clay platelet.
electrical resistivity A measure of the resistance of soil to conduct electricity used to infer the soil water matric potential from predetermined calibrations.
electrokinetic (zeta) potential The electrical potential at the surface of the shear plane between immobile liquid attached to a charged particle and mobile liquid further from the particle surface.
electron acceptor A compound that accepts electrons during biotic or abiotic chemical reactions and is thereby reduced.
electron donor A compound that donates or supplies electrons during metabolism and is thereby oxidized.
electronegativity A measure of the ability of an atom to attract an electron in competition with other atoms.
electrostatic valency The ratio of cation valence to coordination number (z/n).
elevated lake plain (not preferred) Refer to collapsed lake plain, collapsed ice-floored lakebed.
elevation [soil survey] The height of a point on the earth’s surface relative to mean sea level (msl) (Schoeneberger and Wysocki, personal communication, 2013). Compare relief.
elliptical gilgai A type of gilgai dominated by elliptical, closed and semi-closed depressions (micro-lows) separated by low mounds or ridges (micro-highs); the prevailing type of gilgai on mildly sloping terrain (slopes 3–8%); as slope increases, basins become more eccentric and the occurrence of interconnected micro-lows increases (Schoeneberger and Wysocki, personal communication, 2013). Compare circular gilgai, linear gilgai, gilgai.
eluvial horizon A soil horizon that has been formed by the process of eluviation. Compare illuvial horizon.
eluviation The removal of soil material in suspension (or in solution) from a layer or layers of a soil. Usually, the loss of material in solution is described by the term “leaching.” Compare illuviation and leaching.
emitter Refer to irrigation, trickle irrigation, emitter.
end moraine A ridge-like accumulation that is being or was produced at the outer margin of an actively flowing glacier at any given time; a moraine that has been deposited at the outer or lower end of a valley glacier ( Jackson, 1997). Compare terminal moraine, recessional moraine, ground moraine.
endomycorrhiza(e) A mycorrhizal association with intracellular penetration of the host root cortical cells by the fungus as well as outward extension into the surrounding soil. Compare arbuscule; vesicles.
endophyte An organism (e.g., fungus, bacteria) growing within a plant. The association may be symbiotic or parasitic.
endosaturation The soil is saturated with water in all layers from the upper boundary of saturation to a depth of 200 cm or more from the mineral soil surface. Compare episaturation.
energy The property of a system that allows it to do work.
enrichment culture A technique in which environmental (including nutritional) conditions are controlled to favor the development of a specific organism or group of organisms through prolonged or repeated culture.
enrichment ratio (ER) refer to erosion, enrichment ratio (ER).
Entisols [soil taxonomy] An order of mineral soils that have little or no pedogenic development (no distinct subsurface diagnostic horizons within 1 m of the soil surface. Most Entisols have no diagnostic horizons other than an ochric epipedon (rarely they may have either a histic or anthropic epipedon, or an albic horizon). Entisols may have any soil moisture regime and any soil temperature regime, but they do not have permafrost (USDA, 1999; Appendix 1).
entrapped air “isolated air phase that is no longer connected to the atmosphere” that restricts water infiltration into the soil (must get air out to let more water in), or may lead to flow instability and preferential flow.
entropy A measure of the unavailable energy in a system.
enzyme Any of numerous proteins that are produced in the cells of living organisms and function as catalysts in the chemical processes of those organisms.
Eocene An epoch (from 33.9 to 55.8 million years ago) of the Tertiary Period of geologic time that follows the Paleocene epoch and precedes the Oligocene epoch; also the corresponding (time-stratigraphic) “series” of earth materials (Schoeneberger and Wysocki, personal communication, 2013).
eolian Pertaining material transported and deposited by the wind (eolian deposit), including dune sands, sand sheets, loess deposits, and clay (e.g., parna; Hawley and Parsons, 1980).
ephemeral gully
Small channels eroded by concentrated flow that can be easily filled by normal tillage, only to reform again in the same location by additional runoff events.
equivalent diameter In sedimentation analysis of particle size, the diameter assigned to a nonspherical particle; that is, the diameter of a spherical particle of the same density and velocity of fall. Sometimes referred to as the equivalent spherical diameter.
equivalent spherical diameter Refer to equivalent diameter.
eroded fan remnant All, or a portion of an alluvial fan that is much more extensively eroded and dissected than a fan remnant; sometimes called an erosional fan remnant (Peterson, 1981). It consists primarily of (i) eroded and highly dissected sides (eroded fan-remnant sideslopes) dominated by hillslope positions (shoulder, backslope, etc.), and (ii) to a lesser extent an intact, relatively planar, relict alluvial fan “summit” area best described as a tread.
eroded fan-remnant sideslope A rough or broken margin of an eroded fan remnant highly dissected by ravines and gullies that can be just a fringe or make up a large part of an eroded alluvial fan; its bounding escarpments (risers), originally formed by inset channels, have become highly dissected and irregular such that terrace components (tread and riser) have been consumed or modified and replaced by hillslope positions and components (shoulder, backslope, footslope, etc.); sometimes referred to as fan remnant sideslopes (Peterson, 1981). Compare eroded fan remnant (Schoeneberger and Wysocki, personal communication, 2013).
erodibility
(i) The degree or intensity of a soil’s state or condition of, or susceptibility to, being erodible. (ii) The K factor in the Universal Soil Loss Equation. Compare erosion, Universal Soil Loss Equation.
erodible Refer to erosion, erodible.
erosion
(a) The wearing away of the land surface by rain or irrigation water, wind, ice, or other natural or anthropogenic agents that abrade, detach, and remove geologic parent material or soil from one point on the earth’s surface and deposit it elsewhere, including such processes as gravitational creep and so-called tillage erosion. (b) The detachment and movement of soil or rock by water, wind, ice, or gravity. The following terms are used to describe different erosion types, processes, and mechanisms:
erosion surface A land surface shaped by the action of erosion, especially by running water (e.g., Iowan Erosion Surface).
erosion, accelerated erosion Erosion in excess of natural rates, usually as a result of anthropogenic activities. Compare geologic erosion.
erosion, grassed waterway
A natural or constructed waterway, usually broad and shallow, covered with grasses, used to conduct surface water from or through cropland.
erosion, gully A small channel with steep sides cut into unconsolidated materials resulting from erosion and caused by the concentrated but intermittent flow of water usually during and immediately following heavy rains or ice/snow melt. A gully generally is an obstacle to wheeled vehicles and deep enough (usually >0.5 m) to interfere with, and not to be obliterated by, normal tillage operations. Compare erosion, rill, arroyo, draw, ravine, swale.
erosion, rill
An erosion process on sloping fields in which numerous and randomly occurring small channels of only several centimeters in depth are formed; occurs mainly on recently cultivated soils. Compare erosion, rill.
erosive velocity Refer to erosion.
erratic A rock fragment carried by glacial ice, or by floating ice (ice-rafting), and subsequently deposited at some distance from the outcrop from which it was derived, and generally, though not necessarily, resting on bedrock or sediments of different lithology. Coarse fragments range in size from a pebble to a house-size block ( Jackson, 1997).
escarpment A relatively continuous cliff or relatively steep slope, produced by erosion or faulting, breaking the general topographic continuity of more gently sloping land surfaces. The term is most commonly applied to cliffs produced by differential erosion, and it is commonly used synonymously with “scarp” (Schoeneberger and Wysocki, personal communication, 2013; Jackson, 1997; Hawley and Parsons, 1980).
esker A long, narrow, sinuous, steep-sided ridge composed of irregularly stratified sand and gravel that was deposited by a subglacial or supraglacial stream flowing between ice walls, or in an ice tunnel of a retreating glacier, and was left behind as high ground when the ice melted. Eskers range in length from less than a kilometer to more than 160 km, and in height from 3 to 30 m. Compare kame, crevasse filling, glaciofluvial deposits, outwash (Schoeneberger and Wysocki, personal communication, 2013).
essential (chemical) elements Elements required by plants to complete their normal life cycles, which include C, H, O, P, K, N, S, Ca, Fe, Mg, Mn, Cu, B, Zn, Co, Mo, Cl, and Na.
estuarine deposit Fine-grained sediments (very fine sand, silt and clay) of marine and fluvial origin commonly containing decomposed organic matter, laid down in the brackish waters of an estuary; characteristically finer sediments than deltaic deposits. Compare fluviomarine deposit,lacustrine deposit, lagoonal deposit, marine deposit, overbank deposit ( Jackson, 1997).
estuarine subaqueous soils Soils that form in sediment found in shallow-subtidal environments. These soils occur below extreme low water in protected estuarine coves, bays, inlets, and lagoons. Excluded from the definition of these soils are any areas “permanently covered by water too deep (typically greater than 2.5 m) for the growth of rooted plants” (Subaqueous Soils Subcommittee, 2005).
estuary (a) A seaward end or the widened funnel-shaped tidal mouth of a river valley where fresh water comes into contact with seawater and where tidal effects are evident; e.g., a tidal river, or a partially enclosed coastal body of water where the tide meets the current of a stream. (b) A drowned river mouth formed by the subsidence of land near the coast or by the drowning of the lower portion of a non-glacial valley due to the rise of sea level ( Jackson, 1997). Refer to lagoon.
eubacteria Prokaryotes other than archaebacteria.
euic High level of bases in soil material, specified at family level of classification.
eukaryote Cellular organisms having a membrane-bound nucleus within which the genome of the cell is stored as chromosomes composed of DNA; includes algae, fungi, protozoa, plants, and animals.
eutrophic Having concentrations of nutrients optimal, or nearly so, for plant, animal, or microbial growth. (Said of nutrient or soil solutions and bodies of water.) The term literally means “self-feeding.”
eutrophication Condition in an aquatic ecosystem where excessive nutrient concentrations result in high biological productivity, typically associated with algae blooms, that causes sufficient oxygen depletion to be detrimental to other organisms.
evaporation The process by which liquid water from soil vaporizes near the soil surface and is lost to the atmosphere.
evaporites Residue of salts (including gypsum and all more soluble species) precipitated by evaporation.
evapotranspiration The combined loss of water from a given area, and during a specified period of time, by evaporation from the soil surface and by transpiration from plants.
everglades (colloquial – southern USA) A large expanse of marshy land, covered mostly by grasses, e.g., the Florida Everglades ( Jackson, 1997).
exchangeable sodium percentage (ESP) Exchangeable sodium fraction expressed as a percentage.
exchangeable sodium ratio (ESR) The ratio of exchangeable sodium to all other exchangeable cations.
exchangeable anion
A negatively charged ion held on or near the surface of a solid particle by a positive surface charge and which may be easily replaced by other negatively charged ions (e.g., with a Cl– salt).
exchangeable bases
Charge sites on the surface of soil particles that can be readily replaces with a salt solution. In most soils, Ca2+, Mg2+, K+ and Na+ predominate. Historically, these are called bases because they are cations of strong bases. Many soil chemists object to this term because these cations are not bases by any modern definition of the term. Compare base saturation and exchangeable cation.
exchangeable cation A positively charged ion held on or near the surface of a solid particle by a negative surface and which may be replaced by other positively charged ions in the soil solution. Usually expressed in centimoles or millimoles of charge per kilogram.
exchangeable cation percentage (no longer pre-ferred in SSSA publications) The extent to which the
exchangeable nutrient A plant nutrient that is held by the adsorption complex of the soil and is easily exchanged with the anion or cation of neutral salt solutions.
exchangeable sodium fraction The fraction of the cation exchange capacity of a soil occupied by sodium ions.
exfiltration Process of water exiting the soil surface.
exfoliation The process by which concentric scales, plates, or shells of rock, from less than a centimeter to several meters in thickness, are successively spalled or stripped from the bare surface of a large rock mass. It often results in a rounded rock mass or dome-shaped hill ( Jackson, 1997).
exhumed (adjective) Formerly buried landforms, geomorphic surfaces, or paleosols that have been re-exposed by erosion of the covering mantle. Compare relict, buried, ground soil (Hawley and Parsons, 1980).
exoenzymes Enzymes that are excreted by organisms into the surrounding environment and carry out their metabolic or catabolic activity in that location.
experimental plot The smallest area unit in field studies that receives an experimental treatment.
extractable soil nutrient The quantity of a nutrient removed from the soil by a specific soil test procedure.
extragrade (a) A taxonomic class at the subgroup level of soil taxonomy having properties that are not characteristic of any class in a higher category (any order, suborder or great group) and that do not indicate transition to any other known kind of soil. (b) A soil that is a member of one such subgroup. Compare intergrade.
extramorainal (adjective) Said of deposits and phenomena occurring outside the area occupied by a glacier and it’s lateral and end moraines ( Jackson, 1997). Compare intramorainal.
extramorainic (not preferred) Use extramorainal.
extrusive (adjective) Said of igneous rocks and sediments derived from deep-seated molten matter (magmas), deposited and cooled on the earth’s surface (e.g., including lava flows and tephra deposits; Hawley and Parsons, 1980). Compare intrusive, volcanic.
exudate, root Low molecular weight metabolites that enter the soil from plant roots.