economic rate: The application rate of material, usually fertilizer, that gives the highest economic returns for the crop produced.
edaphic: (i) Of or pertaining to the soil. (ii) Resulting from or influenced by factors inherent in the soil or other substrate, rather than by climatic factors.
effective precipitation: That portion of the total rainfall precipitation which becomes available for plant growth.
effective stress: The stress transmitted through a soil by intergranular pressures.
eluvial horizon: A soil horizon that has been formed by the process of eluviation.
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."
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.
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.
Entisols: Mineral soils that have no distinct subsurface diagnostic horizons within 1 m of the soil surface.
eolian: Pertaining to earth material transported and deposited by the wind including dune sands, sand sheets, loess, and parna.
ephemeral stream: A stream, or reach of a stream, that flows only in direct response to precipitation. It receives no protracted supply from melting snow or other source, and its channel is, at all times, above the water table.
episaturation: The soil is saturated with water in one or more layers within 200 cm of the mineral soil surface and also has one or more unsaturated layers with an upper boundary above 200 cm depth, below the saturated layer(s) (a perched water table).
erosion: (i) 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; (ii) 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.
escarpment: A relatively continuous cliff or relatively steep slope, produced by erosion or faulting, breaking the general 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."
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 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.
estuary: 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.
euic: High level of bases in soil material, specified at family level of classification.
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."
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.
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.
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 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.
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: (i) 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. (ii) A soil that is a member of one such subgroup.
exudate, root: Low molecular weight metabolites that enter the soil from plant roots.family, soil: In soil classification one of the categories intermediate between the subgroup and the soil series. Families provide groupings of soils with ranges in texture, mineralogy, temperature, and thickness.
fen: A peat accumulating wetland that receives some drainage from surrounding mineral soils and usually supports marsh-like vegetation. These areas are richer in nutrients and less acidic than bogs. The soils under fens are peat (Histosols) if the fen has been present for a while.
fermentation: The metabolic process in which an organic compound serves as both an electron donor and the final electron acceptor.
ferrolysis. Clay destruction process involving disintegration and solution in water based upon the alternate reduction and oxidation of iron.
fertility, soil: The relative ability of a soil to supply the nutrients essential to plant growth.
fertilizer: Any organic or inorganic material of natural or synthetic origin (other than liming materials) that is added to a soil to supply one or more plant nutrients essential to the growth of plants.
fibric material: Organic soil material that contains 3/4 or more recognizable fibers (after rubbing between fingers) of undecomposed plant remains. Bulk density is usually very low and water holding capacity very high.
film water: A thin layer of water, in close proximity to soil-particle surfaces, that varies in thickness from 1 or 2 to perhaps 100 or more molecular layers.
fine sand: (i) A soil separate. (See also soil separates.) (ii) A soil textural class.
fire, ground (forestry): A fire that consumes all organic material of the forest floor and also burns into the underlying soil itself, as, for example, a peat fire. Differentiated from a surface fire on the basis of vulnerability to wind; in a surface fire the flames are visible and burning is accelerated by wind, whereas, in a ground fire, wind is generally not a serious factor.
first bottom: The lowest and most frequently flooded part of the flood plain of a stream.
fixation: The process by which available plant nutrients are rendered less available or unavailable in the soil. Not to be confused with dinitrogen fixation.
flagstone: A relatively thin, flat rock fragment, from 150 to 380 mm on the long axis.
flexible cropping: A strategy of growing adapted crops with cropping and fallow decisions at each prospective date of planting based on available water in the soil plus expected growing season precipitation and without regard to a predetermined rigidly adhered to cropping sequence.
flocculation: The coagulation of colloidal soil particles due to the ions in solution. In most soils the clays and humic substances remain flocculated due to the presence of doubly and triply charged cations.
flood plain: The nearly level plain that borders a stream and is subject to inundation under flood-stage conditions unless protected artificially. It is usually a constructional landform built of sediment deposited during overflow and lateral migration of the stream.
flooding: Accumulation of large amounts of runoff on the landscape as a result of rainfall in excess of the soil's ability to drain water from the landscape before extensive inundation and ponding occurs.
flow velocity (of water in soil): The volume of water transported per unit of time and per unit of cross-sectional area normal to the direction of water flow.
flowtill: A supraglacial till that is modified and transported by mass flow.
flux: The time rate of transport of a quantity (e.g., mass or volume of fluid, electromagnetic energy, number of particles, or energy) across a given area.
forest floor: All organic matter generated by forest vegetation, including litter and unincorporated humus, on the mineral soil surface.
forest productivity: The capacity of a forest to produce specific products (i.e. biomass, lumber) over time as influenced by the interaction of vegetative manipulation and abiotic factors (i.e. soil, climate, physiography). Net primary productivity (NPP) provides the fundamental measure of forest productivity. When measured at the point of foliar carrying capacity for all potential flora, NPP is a measure of potential site productivity. Rate of product growth, an economic component, is occasionally used as a partial measure of forest productivity.
fragile land: Land that is sensitive to degradation when disturbed; such as with highly erodible soils, soils where salts can and do accumulate, and soils at high elevations.
frost (concrete): Ice in the soil in such quantity as to constitute a virtually solid block.
geomorphology: The science that studies the evolution of the earth's surface. The science of landforms. The systematic examination of landforms and their interpretation as records of geologic history.
gilgai: The microrelief of small basins and knolls or valleys and ridges on a soil surface produced by expansion and contraction during wetting and drying (usually in regions with distinct, seasonal, precipitation patterns) of clayey soils that contain smectite.
glacial drift: A general term applied to all mineral material transported by a glacier and deposited directly by or from the ice, or by running water emanating from a glacier. Drift includes unstratified material (till) that forms moraines, and stratified glaciofluvial deposits that form outwash plains, eskers, kames, varves, and glaciolacustrine sediments.
glaciers: Large masses of ice that formed, in part, on land by the compaction and recrystallization of snow. They may be moving downslope or outward in all directions because of the stress of their own weight or they may be retreating or be stagnant.
green manure: Plant material incorporated into soil while green or at maturity, for soil improvement.
greenhouse effect: The absorption of solar radiant energy by the earth's surface and its release as heat into the atmosphere; longer infrared heat waves are absorbed by the air, principally by carbon dioxide and water vapor, thus, the atmosphere traps heat much as does the glass in a greenhouse.
ground moraine: An extensive layer of till, having an uneven or undulating surface; a deposit of rock and mineral debris dragged along, in, on, or beneath a glacier and emplaced by processes including basal lodgement and release from downwasting stagnant ice by ablation.
ground water: That portion of the water below the surface of the ground at a pressure equal to or greater than atmospheric.
gullied land: Areas where all diagnostic soil horizons have been removed by water, resulting in a network of V-shaped or U-shaped channels. Some areas resemble miniature badlands. Generally, gullies are so deep that extensive reshaping is necessary for most uses.
gypsan: A cutan composed of gypsum.
gypsic horizon: A mineral soil horizon of secondary CaSO4 enrichment that is >15 cm thick, has at least 50 g kg-1 more gypsum than the C horizon, and in which the product of the thickness in centimeters and the amount of CaSO4 is equal to or greater than 1500g kg-1.
gyttja: Sedimentary peat consisting mainly of plant and animal residues precipitated from standing water.hardpan: A soil layer with physical characteristics that limit root penetration and restrict water movement.
hardsetting soil: Soils that, following wetting, exhibit transient but only slowly reversible cementation and/or induration throughout significant fractions of the profile restrictive to seed emergence and root penetration (Australian).
heat of immersion: The heat evolved on immersing a soil, at a known initial water content (usually oven dry) in a large volume of water.
heavy metals: Those metals which have densities >5.0 Mg m-3. In soils these include the elements Cd, Co, Cr, Cu, Fe, Hg, Mn, Mo, Ni, Pb, and Zn.
heavy soil (colloquial): A soil with a high content of the fine separates, particularly clay, or one with a high drawbar pull and hence difficult to cultivate, especially when wet. (See also fine texture.)
hematite: Fe2O3. A red iron oxide mineral that contributes red color to many soils.
hemic material: Organic soil material at an intermediate degree of decomposition that contains 1/6 to 3/4 recognizable fibers (after rubbing) of undecomposed plant remains. Bulk density is usually very low, and water holding capacity very high.
heterotroph: An organism able to derive carbon and energy for growth and cell synthesis by utilizing organic compounds.
histic epipedon: A thin organic soil horizon that is saturated with water at some period of the year unless artificially drained and that is at or near the surface of a mineral soil. The histic epipedon has a maximum thickness depending on the kind of materials in the horizon and the lower limit of organic carbon is the upper limit for the mollic epipedon.
Histosols: Organic soils that have organic soil materials in more than half of the upper 80 cm, or that are of any thickness if overlying rock or fragmental materials that have interstices filled with organic soil materials.
horizonation: The development of horizons in soil as a result of a soil forming process or a combination of soil forming processes.
hue: A measure of the chromatic composition of light that reaches the eye; one of the three variables of color.
humic acid: The dark-colored organic material that can be extracted from soil with dilute alkali and other reagents and that is precipitated by acidification to pH 1 to 2.
humus: Total of the organic compounds in soil exclusive of undecayed plant and animal tissues, their "partial decomposition" products, and the soil biomass. The term is often used synonymously with soil organic matter.
hybridization: The binding or annealing of two, complementary, single strands of nucleic acid.
hydrated lime: A liming material composed mainly of calcium and magnesium hydroxides that reacts quickly to neutralize acid soils.
hydric soils: Soils that are wet long enough to periodically produce anaerobic conditions, thereby influencing the growth of plants.
hydrodynamic dispersion: The process wherein the solute concentration in flowing solution changes in response to the interaction of solution movement with the pore geometry of the soil, a behavior with similarity to diffusion but only taking place when solution movement occurs.
hydrogenic soil: Soil developed under the influence of water standing within the profile for considerable periods; formed mainly in cold, humid regions.
hydrologic cycle: The fate of water from the time of precipitation until the water has been returned to the atmosphere by evaporation and is again ready to be precipitated.
hydrophobic soils: Soils that are water repellent, often due to dense fungal mycelial mats or hydrophobic substances vaporized and reprecipitated during fire.
hyperthermic: A soil temperature regime that has mean annual soil temperatures of 22°C or more and >5°C difference between mean summer and mean winter soil temperatures at 50 cm below the surface. Isohyperthermic is the same except the summer and winter temperatures differ by <5°C.
hypha (pl. hyphae): Filament of fungal cells. Many hyphal filaments (hyphae) constitute a mycelium. Bacteria of the order Actinomycetales also produce branched mycelium.
hysteresis: A nonunique relationship between two variables, wherein the curves depend on the sequences or starting point used to observe the variables. Examples include the relationships: (i) between soil-water content and soil-water matric potential, (ii) between solution concentration and adsorbed quantity of chemical species, and (iii) between soil volume and water content for swelling and shrinking soils.
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