Glossary of Soil Science Terms - Browse
s-matrix (of a soil material) The material within the simplest peds, or composing apedal soil materials, in which the pedological features occur; it consists of the plasma, skeleton grains, and voids that do not occur as pedological features other than those expressed by specific extinction (orientation) patterns. Pedological features also have an internal s-matrix.
saddle A low point on a ridge or interfluve, generally a divide (pass, col) between the heads of streams flowing in opposite directions (Hawley and Parsons, 1980). Compare summit, crest.
sag A small, partially or completely closed depression formed by movement along a strike-slip fault, or by mass movement (i.e., landslide) that may or may not temporarily pond water from impounded drainage or surface runoff. For example, a closed depression formed between a scarp or headwall and an adjacent rotated slump block of a landslide (Schoeneberger and Wysocki, personal communication, 2013).
sag pond A small, permanent body of water in a semiclosed or closed depression formed by movement along a strike-slip fault or by mass movement (i.e., landslide) that ponds water from impounded drainage or surface runoff. Also spelled sagpond (Schoeneberger and Wysocki, personal communication, 2013; Jackson, 1997).
salic horizon
[soil taxonomy] A diagnostic, subsurface mineral soil horizon of enrichment with secondary salts that are more soluble in cold water than gypsum. A salic horizon is 15 cm or more in thickness, contains at least 20 g kg-1 salt, and the product of the thickness in centimeters and amount of salt by weight is >600 g kg-1 (USDA, 1999).
Salids [soil taxonomy] A suborder of Aridisols that have an accumulation of an excessive amount of salts that are more soluble than gypsum. They have a salic horizon that has its upper boundary within 100 cm of the soil surface. The soil temperature regime is frigid or warmer. Salids have an aridic soil moisture regime. As a rule, Salids are unsuitable for agricultural use (USDA, 1999; Appendix I).
saline seep Intermittent or continuous saline water discharge at or near the soil surface under dryland conditions that reduces or eliminates crop growth. It is differentiated from other saline soil conditions by recent and local origin, shallow water table, saturated root zone, and sensitivity to cropping systems and precipitation.
saline soil
A nonsodic soil containing sufficient soluble salt to adversely affect the growth of most crop plants. The lower limit of saturation extract electrical conductivity of such soils is conventionally set at 4 dS m-1 (at 25°C). Actually, sensitive plants are affected at half this salinity and highly tolerant ones at about twice this salinity.
saline-alkali soil
(no longer used in SSSA publications) (a) A soil containing sufficient exchangeable sodium to interfere with the growth of most crop plants and containing appreciable quantities of soluble salts. The exchangeable-sodium percentage is >15, the conductivity of the saturation extract >4 dS m-1 (at 25°C), and the pH is usually 8.5 or less in the saturated soil. (b) A saline-alkali soil has a combination of harmful qualities of salts and either a high alkalinity or high content of exchangeable sodium, or both, so distributed in the profile that the growth of most crop plants is reduced. Compare saline-sodic soil.
saline-sodic soil
A soil containing sufficient exchangeable sodium to interfere with the growth of most crop plants and containing appreciable quantities of soluble salts. The exchangeable sodium ratio is greater than 0.15, conductivity of the soil solution, at saturated water content, of >4 dS m-1 (at 25°C), and the pH is usually 8.5 or less in the saturated soil. Compare saline-alkali soil.
salinity, soil The amount of soluble salts in a soil. The conventional measure of soil salinity is the electrical conductivity of a saturation extract.
salinization The process whereby soluble salts accumulate in the soil.
salt balance The quantity of soluble salt removed from an irrigated area in the drainage water minus that delivered in the irrigation water.
salt flats [soil survey] A miscellaneous area (map unit) applied to undrained flats in arid regions that have surface deposits of secondary crystalline salt overlying stratified and strongly saline sediment (USDA, 1993).
salt marsh Flat, poorly drained area that is subject to periodic or occasional overflow by salt water, containing water that is brackish to strongly saline, and usually covered with a thick mat of grassy halophytic plants; e.g., a coastal marsh periodically flooded by the sea, or an inland marsh, (or salina) in an arid region and subject to intermittent overflow by salty water ( Jackson, 1997). Compare tidal marsh, mud flat.
salt pond A large or small body of salt water in a marsh or swamp along the seacoast ( Jackson, 1997).
salt tolerance The ability of plants to resist the adverse, nonspecific effects of excessive soluble salts in the rooting medium.
salt-affected soil Soil that has been adversely modified for the growth of most crop plants by the presence of soluble salts, with or without high amounts of exchangeable sodium. Compare saline soil, saline-sodic soil, and sodic soil.
saltation Refer to erosion, saltation.
saltation flux Refer to erosion, saltation flux.
sample A part of a population taken to estimate a parameter of the whole population.
sample plot An area of land, usually small, used for measuring or observing performance under existing or applied treatments.
sand (a) A soil separate. Compare soil separates. (b) A soil textural class. Compare soil texture.
sand plain [geomorphology] A sand-covered plain which may originate by deflation of sand dunes, and whose lower limit of erosion is governed by the water table. Also spelled sandplain ( Jackson, 1997).
sand ramp A sand sheet blown up onto the lower slopes of a bedrock hill or mountain and forming an inclined plane, sometimes filling small mountain-side valleys and even crossing low passes (Schoeneberger and Wysocki, personal communication, 2013; Peterson, 1981). Compare climbing dune, sand sheet.
sand sheet A large, irregularly shaped, commonly thin, surficial mantle of eolian sand, lacking the discernible slip faces that are common on dunes.
sand boil An accumulation of sand commonly in the form of a low mound, produced by the expulsion of liquefied sand to the ground surface; sometimes called sand volcanoes (not preferred). Examples are found on top of some landslide deposits (i.e., spreads) or on the upper surface of highly contorted layers of laminated sediments (Schoeneberger and Wysocki, personal communication, 2013; Jackson, 1997).
sand dune (not preferred) Refer to dune.
sand flow [mass movement] A flow of wet sand, as along banks of noncohesive clean sand that is subject to scour and to repeated fluctuations in pore-water pressure due to rise and fall of the tide ( Jackson, 1997).
sand pit A depression, ditch or pit excavated to furnish sand for roads or other construction purposes offsite; a type of borrow pit (Schoeneberger and Wysocki, personal communication, 2013).
sand ridge (a) (not preferred) An imprecise, generic name for any low ridge of sand, formed at some distance from shore, e.g., submerged (longshore bar) or emergent (barrier beach). (b) One of a series of long, wide, extremely low, parallel ridges believed to represent the eroded stumps of former longitudinal sand dunes, as in western Zimbabwe. ( Jackson, 1997).
sand volcano (not preferred) Use sand boil.
sand wedge (not preferred) Use ice wedge cast.
sandhills A region of semi-stabilized sand dunes or sandy hills, either covered with vegetation or bare, as in north-central Nebraska and the midlands of the Carolinas ( Jackson, 1997).
sandstone Sedimentary rock containing dominantly sand-size clastic particles (Hawley and Parsons, 1980).
sandur (not preferred) Refer to outwash plain.
sandur (not preferred) Use outwash plain.
sandy (a) Texture group consisting of sand and loamy sand textures. Compare soil texture. (b) Family particle-size class for soils with sand or loamy sand textures and <35% rock fragments in upper subsoil horizons.
sandy clay A soil textural class. Compare soil texture.
sandy clay loam A soil textural class. Compare soil texture.
sandy loam A soil textural class. Compare soil texture.
sanitary landfill A land area where municipal solid waste is buried in a manner engineered to minimize environmental degradation. Commonly the waste is compacted and ultimately covered with soil or other earthy material. Compare dump ( Jackson, 1997).
saponite A trioctahedral smectite containing magnesium with the majority of the charge originating in the tetrahedral layers.
sapric material Organic soil material that contains less than 1/6 recognizable fibers (after rubbing) of undecomposed plant remains. Bulk density is usually very low, and water holding capacity very high.
Saprists
[soil taxonomy] A suborder of Histosols that are wet and have a high content of well decomposed plant materials (so well decomposed that the botanical origin of the organic material cannot be determined), and a bulk density of more than 0.2 Mg m-3. The fiber content is less than one-sixth after rubbing between the thumb and fingers. Saprists are saturated with water for periods long enough to limit their use for most crops unless they are artificially drained; the ground water table tends to fluctuate within the soils (USDA, 1999; Appendix I).
saprolite Soft, friable, isovolumetrically weathered bedrock that retains the fabric and structure of the parent rock exhibiting extensive intercrystal and intracrystal weathering; highly weathered bedrock. In pedology, saprolite was formerly applied to any unconsolidated residual material underlying the soil and grading to hard bedrock below (Schoeneberger and Wysocki, personal communication, 2013). Compare grus, residuum.
saprophyte An organism that lives on dead organic material.
saprophytic competence The ability of a nodule symbiont or pathogenic microorganism to establish itself and live in soil as a saprophyte.
sate (synonym of satiate) To fill most of the pores between soil particles with liquid, the lack of complete filling being caused by the entrapment of air as water enters the soil.
satiate (sate) The state in which soil is under positive soil water pressure but is not fully saturated due to entrapped air.
saturate
(a) To fill all the voids between soil particles with a liquid. (b) To form the most concentrated solution possible under a given set of physical conditions in the presence of an excess of the solute. (iii) To fill to capacity, as the adsorption complex with a cation species; e.g., H+-saturated, etc.
saturated soil paste A particular mixture of soil and water. At saturation, the soil paste glistens as it reflects light, flows slightly when the container is tipped, and the paste slides freely and cleanly from a spatula.
saturation content The mass water content of a saturated soil paste.
saturation extract The solution extracted from a soil at its saturation water content.
scabland An elevated, flat-lying, basalt-floored area, with little if any soil cover, sparse vegetation, and usually deep, dry channels scoured into the surface, especially by glacial meltwaters such as the Channeled Scablands of eastern Washington ( Jackson, 1997). Compare coulee.
scaling exponent
Exponent relating two variables, for example area scales as (is proportional to) length2, and capillary rise scales as pore radius–1.
scalped area A modified slope, feature, or land area where much or all of the natural soil has been mechanically removed (e.g., scraped off) due to construction or other management practices (Schoeneberger and Wysocki, personal communication, 2013). Compare – truncated soil.
scalping A method of preparing forest soils for planting or seeding that consists of removing the ground vegetation and root mat to expose mineral soil.
scarifying Refer to tillage, scarifying.
scarp An escarpment, cliff, or steep slope of some extent along the margin of a plateau, mesa, terrace, or structural bench. A scarp may be of any height.
scarp slope The relatively steeper face of a cuesta, facing in a direction opposite to the dip of the strata. Compare dip slope ( Jackson, 1997).
scoria [geology] Vesicular, rock fragments (no size restrictions) with a specific gravity > 2.0, or a cindery crust of such material on the surface of andesitic or basaltic lava; the vesicular nature is due to the escape of volcanic gases before solidification; it is usually heavier, darker, and more crystalline than pumice (Schoeneberger and Wysocki, personal communication, 2013). Compare cinder, pumice, tephra.
scoria land [soil survey] A miscellaneouas area (map unit) applied to surficial deposits of slag-like clinkers, burned shale or fine-grained sandstone remaining after coal beds burn out; not applied to volcanic scoria aeas (USDA, 1993). Compare porcellanite.
scour [geomorphology] The process of powerful and concentrated clearing and digging action of flowing air, water, or ice, especially the downward erosion by stream water in sweeping away mud and silt on the outside curve of a bend, or during the time of a flood ( Jackson, 1997).
scour channel A place in a stream bed swept (scoured) by running water, generally leaving a gravel bottom ( Jackson, 1997).
scour and fill [geomorphology] A process of alternate excavation and refilling of a channel, as by a stream or the tides; especially such a process occurring in time of flood, when the discharge and velocity of an aggrading stream are suddenly increased, causing the digging of new channels that become filled with sediment when the flood subsides. Compare cut and fill ( Jackson, 1997).
scree A collective term for an accumulation of coarse rock debris or a sheet of coarse debris mantling a slope. Scree is not a synonym of talus, as scree includes loose, coarse fragment material on slopes without cliffs (Hawley and Parsons, 1980). Compare talus, colluvium, mass movement.
scree slope A portion of a hillside or mountainslope mantled by scree and lacking an up-slope rockfall source (i.e., cliff; Schoeneberger and Wysocki, personal communication, 2013). Compare talus slope, scree, talus.
screefing A method of preparing forest soils for planting or seeding that consists of mechanically pushing aside the humus layer to expose mineral soil.
screen (a) (wells) A manufactured well casing with precisely dimensioned and shaped openings. (Compare with perforated casing.) (b) (canals) A device used to clean surface water of debris, such as revolving screens or turbulent fountain screens.
scroll (not preferred) Use meander scroll.
sea (a) A large inland body of salt water (e.g., the Salton Sea, CA). (b) A geographic subdivision of an ocean (e.g., the South China Sea; Schoeneberger and Wysocki, personal communication, 2013; Jackson, 1997). Compare gulf, ocean.
sea cliff A cliff or slope produced by wave erosion, situated at the seaward edge of the coast or the landward side of the wave-cut platform. It may vary from an inconspicuous slope to a high, steep escarpment ( Jackson, 1997).
seal Refer to surface sealing.
second bottom (obsolete; informal) The first terrace above the normal flood plain of a stream.
secondary metabolite A product of intermediary metabolism released from a cell.
secondary mineral A mineral resulting from the decomposition of a primary mineral or from the reprecipitation of the products of decomposition of a primary mineral. Compare primary mineral.
secondary nutrients Refers to Ca, Mg, and S in fertilizers.
sediment Transported and deposited particles or aggregates derived from rocks, soil, or biological material.
sediment yield The amount of eroded soil that is delivered to a point in a watershed or transported out of a stream section over a period of time. It includes the contributions of erosion from slopes, channels, and a mass wasting of streambanks minus the sediment deposited before the point of interest.
sedimentary peat [soil taxonomy] An accumulation of organic material that is predominantly the remains of floating aquatic plants (e.g., algae) and the remains and fecal material of aquatic animals, including coprogenous earth (Soil Survey Staff, 1993). Compare herbaceous peat, moss peat, woody peat, peat, muck, and mucky peat.
sedimentary rock A more or less consolidated rock formed from clastic materials deposited from suspension or precipitated from solution The principal sedimentary rocks are sandstones, shales, limestones, and conglomerates. Compare sediment.
sedimentation The process of sediment deposition.
sedimentology The science dealing with the study of processes of sedimentation and sediment properties.
seedbed Refer to tillage, seedbed.
seedling emergence That point in time when a young plant grown from seed first breaks through the soil surface.
seep (noun) An area, generally small, where water or oil percolates slowly to the land surface. For water, it may be considered as a seepage spring, but it is used by some for flows too small to be considered as springs ( Jackson, 1997).
seepage erosion Erosion process typically involved in gully formation and bank failure in which subsurface flow exiting the soil transports soil particles entrained in the seepage water.
segregated ice Massive ice in a soil pedon, which is relatively free of soil particles.
seif dune A large, sharp-crested, elongated, longitudinal (linear) dune or chain of sand dunes, oriented parallel, rather than transverse (perpendicular), to the prevailing wind. If unmodified, the crest, in profile, commonly consists of a succession of curved slip faces produced by strong, but infrequent cross winds. A seif dune may be as much as 200 m high and from 400 m to more than 100 km long ( Jackson, 1997; Hawley and Parsons, 1980). Compare longitudinal dune.
selective enrichment A technique for specifically encouraging the growth of a particular organism or group of organisms. Compare enrichment culture.
selective cutting (forestry) A system of cutting in which trees, usually the largest, or small groups of such trees are removed for commercial production or to encourage reproduction under the remaining stand in the openings.
selectivity coefficient A conditional equilibrium coefficient for an ion exchange reaction that is expressed in terms of concentration variables for the exchangeable ions and either concentration variables or activities of the ions in solution.
self-mulching soil A soil in which the surface layer becomes so well aggregated that it does not crust and seal under the impact of rain but instead serves as a surface mulch upon drying.
semi-bolson
(colloquial: western USA) A wide desert basin or valley that is drained by an intermittent stream, an externally drained (open) intermontane basin (Jackson, 1997). Compare bolson.
semipermeable A membrane or interface that permits some substances to move through and restricts movement of other substances. Examples are live biological tissue (i.e., root surface or microbe meberane), the air–water interface (allows water vapor movement but not dissolved salts), and some clay layers (clay skins on peds, clay layer separating fresh ground water above from salty ground water below.
sensor Any device that gathers electromagnetic radiation (EMR) or other energy and presents it in a form suitable for obtaining information about the environment. Passive sensors, such as thermal infrared and microwave, utilize EMR produced by the surface or object being sensed. Active sensors, such as radar, supply their own energy source. Aerial cameras use natural or artificially produced EMR external to the object or surface being sensed.
separate, soil Refer to soil separate.
sepiolite Si12Mg8O30(OH)4(OH2)•8H2 A fibrous clay mineral composed of two silica tetrahedral sheets and one magnesium octahedral sheet that make up the 2:1 layer. The 2:1 layers occur in strips with an average width of three linked tetrahedral chains joined at the edges to form tunnels where water molecules are held.
sequum (pl. sequa) A B horizon together with any overlying eluvial horizons.
series, soil Refer to soil series.
serpentine
A trioctahedral 1:1 type layer silicate: (Mg, Fe)Si2O5(OH)4.
sesquan A cutan composed of a concentration of sesquioxides.
sesquioxides A general term for oxides and hydroxides of iron and aluminum.
sewage lagoon Any artificial pond or other water-filled excavation for the natural oxidation of sewage or disposal of animal manure ( Jackson, 1997).
shale Sedimentary rock formed by induration of a clay, silty clay, or silty clay loam deposit and having the tendency to split into thin layers, i.e., fissility (Hawley and Parsons, 1980).
shatter Refer to tillage, shatter.
shear Force, as with a tillage tool, acting at a right angle to the direction of movement of the tillage implement.
shear strength The maximum resistance of a soil to shearing stresses.
shearing Refer to tillage, shearing.
sheep tracks (not recommended) Use terracettes.
sheet erosion Refer to erosion.
sheet of polyhedra Refer to phyllosilicate mineral terminology.
shelter belt Refer to erosion, windbreak.
shield volcano
A volcano having the shape of a very broad, gently sloping dome, built by flows of very fluid basaltic lava or rhyolitic ash flows (Jackson, 1997; MacDonald and Abbott, 1970). Compare stratovolcano.
shoal (noun) (a) A relatively shallow place in a stream, lake, sea, or other body of water; a shallows. (b) A natural, subaqueous ridge, bank, or bar consisting of, or covered by, sand or other unconsolidated material, rising from the bed of a body of water (e.g., estuarine floor) to near the surface. It may be exposed at low water. Compare reef. (Subaqueous Soil Subcommittee, 2005; Jackson, 1997).
shore
The narrow strip of land immediately bordering any body of water, esp. the sea or a large lake; specifically the zone over which the ground is alternately exposed and covered by tides or waves, or the zone between high water and low water (Jackson, 1997).
shore complex Generally a narrow area that parallels a coastline, commonly cutting across diverse inland landforms, and dominated by landforms derived from active coastal processes which give rise to beach ridges, washover fans, beaches, dunes, wave-cut platforms, barrier islands, cliffs, etc. (Schoeneberger and Wysocki, personal communication, 2013).
shoreline
The intersection of a specified plane of water with the beach; it migrates with changes of the tide or of the water level. Compare shore complex, beach, swash zone (Jackson, 1997).
shoulder [geomorphology] The hillslope-profile position that forms the convex, erosional uppermost inclined surface near the top of a slope. If present, it comprises the transition zone from summit to backslope. Compare summit, crest, backslope, footslope, and toeslope (Schoeneberger and Wysocki, personal communication, 2013; Hawley and Parsons, 1980).
shrink--swell clay Clays which have expandible or collapsible properties, such as smectites with 2:1 lattice structure.
shrinkage, soil
The process of soil material contracting to a lesser volume when subject to loss of water.basic shrinkage phase (or zone) The middle phase of soil shrinkage between the structural and residual shrinkage; it refers to the fundamental shrinkage process of a specified soil.isotropic shrinkage Shrinkage that occurs equally in all directions.moisture ratio Volume water per volume of soil (m3 m-3).ped (shrinkage) A naturally occurring unit of soil defined by surrounding lines of weakness; the smallest unit of natural soil with no internal shrinkage cracks.residual shrinkage Shrinkage that is less than volume water loss during the final stages of drying. shrinkage characteristic The relationship between the soil volume and volume of water contained in a specified soil mass or ped (m3 m-3).shrinkage coefficient The change in soil bulk volume with change in mass water content at a constant stress; also equivalent to, the rate of change in void ratio with moisture ratio at a constant stress. structural shrinkage Shrinkage that is less than volume water loss due to water drainage from macropores at high soil water content.
shrink–swell clay Clays which have expandible or collapsible properties, such as smectites with 2:1 lattice structure.
shrub-coppice dune A small, streamlined dune that forms around desert, brush-and-clump vegetation.
side slope [geomorphology] A geomorphic component of hills consisting of a laterally planar area of a hillside, resulting in predominantly parallel overland water flow (e.g., sheet wash); contour lines generally form straight lines. Side slopes are dominated by colluvium and slope wash sediments. Slope complexity (downslope shape) can range from simple to complex (Schoeneberger and Wysocki, personal communication, 2013). Compare base slope, head slope, nose slope.
siderophore A nonporphyrin metabolite secreted by certain microorganisms that forms a highly stable coordination compound with iron. There are two major types: catecholate and hydroxamate.
sidewall (not preferred) Use glacial-valley wall.
Sierozem [soil classification] A zonal great soil group consisting of soils with pale grayish A horizons grading into calcareous material at a depth of 30 cm (12 in) or less, and formed in temperate to cool, arid climates under a vegetation of desert plants, short grass, and scattered brush. (Not used in soil taxonomy.)
significant [statistics] A term applied to differences, correlation, etc., to indicate that they are probably not due to chance alone; usually indicates a probability of not less than 95%.
silica--alumina ratio The molecules of silicon dioxide (SiO2) per molecule of aluminum oxide (Al2O3) in clay minerals or in soils.
silica--sesquioxide ratio
The molecules of silicon dioxide (SiO2) per molecule of aluminum oxide (Al2O3) plus ferric oxide (Fe2O3) in clay minerals or in soils.
silica–alumina ratio The molecules of silicon dioxide (SiO2) per molecule of aluminum oxide (Al2O3) in clay minerals or in soils.
silica–sesquioxide ratio The molecules of silicon dioxide (SiO2) per molecule of aluminum oxide (Al2O3) plus ferric oxide (Fe2O3) in clay minerals or in soils.
sill [intrusive rocks] A tabular, igneous intrusion that parallels the bedding or foliation of the surrounding sedimentary or metamorphic rock ( Jackson, 1997). Compare dike.
silt (a) A soil separate. Compare soil separates. (b) A soil textural class. Compare soil texture.
silt loam A soil textural class. Compare soil texture.
silting The deposition of silt from a body of standing water; choking, filling, or covering by stream-deposited silt that occurs in a place of retarded flow or behind a dam or reservoir. The term often includes particles from clay to sand-size.
siltite A compact, weakly metamorphosed rock formed by alteration of siltstone, mudstone or silty shale. Siltite is more indurated than mudstone or shale and lacks either shale fissility or slate-like cleavage. Siltite differs from argillite in that silt-size grains (0.002 to 0.062 mm) dominate the matrix rather than clay-size particles (<0.002 mm). Siltite differs from siltstone, mudstone, or shale in that it exhibits very low to low grade metamorphic or diagenetic layer silicate and feldspar alteration to sericite, chlorite, and albite (subgreenschist to greenschist metamorphic facies; Schoeneberger and Wysocki, personal communication, 2013).
siltstone An indurated silt having the texture and composition of shale but lacking its fine lamination or fissility; a massive mudstone in which silt predominates over clay( Jackson, 1997).
silty clay A soil textural class. Compare soil texture.
silty clay loam A soil textural class. Compare soil texture.
single chain
Arrangement resulting from silica tetrahedra sharing two oxygen per tetrahedron and linked linearly: silicon-oxygen ratio is SiO2-.
sinkhole A closed, circular or elliptical depression, commonly funnel-shaped, characterized by subsurface drainage and formed either by solution of the surficial bedrock (e.g., limestone, gypsum, or salt; i.e., solution sinkhole) or by collapse of underlying caves (collapse sinkhole); diameters range from a few meters to as much as 1000 m. Complexes of sinkholes in carbonate-rock terrain are the main components of karst topography (Schoeneberger and Wysocki, personal communication, 2013; White, 1988). Synonym (not preferred) doline. Compare karst valley, interior valley, cockpit.
sinkhole karst A landscape dominated by subsurface drainage and sinkholes (dolines) that range widely in sizes and density; the most common type of karst in upland areas of temperate regions (e.g., Highland Rim of TN, northern FL, southwestern MO, etc.); also called doline karst (not preferred; Schoeneberger and Wysocki, personal communication, 2013; White, 1988; Jackson, 1997). Compare fluviokarst, pavement karst, glaciokarst, karst.
siphon tubes Refer to irrigation, siphon tubes.
site A volume defined by the abiotic factors (i.e., climate, soil, physiography) that influence vegetation growth and development.
site index The height of the dominant and codominant trees (not suppressed during development) at an index age, commonly 25, 50, or 100 years. Used in conjunction with volume tables, site index provides an indication of relative site production.
site productivity The capacity of a site to produce specific products (i.e., biomass or lumber volume) for a given vegetative configuration over time as influenced by abiotic factors (i.e., soil, climate, physiography). Net primary productivity (NPP) provides the fundamental measure of site productivity. When measured at the point of leaf 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 site productivity.
site quality A relative measure of the vegetative production capacity of a site for a given purpose.
skeletan A cutan composed of skeleton grains.
skeleton grains Individual grains that are relatively stable and not readily translocated, concentrated, or reorganized by soil-forming processes; they include mineral grains and resistant siliceous and organic bodies larger than colloidal size.
skew planes Planar voids that traverse the soil material in an irregular manner, having no specific distribution or orientation pattern between individuals.
skid trail Irregularly spaced, roughly linear to radial depressions or small mounds associated with shallow to deep soil disturbance caused by dragging logs across a slope from where they were cut down to a central processing area such as a log landing during timber harvest operations (Schoeneberger and Wysocki, personal communication, 2013).
slick spots [soil survey] A miscellaneous area (map unit) applied to areas with puddle or crusted, very smooth, nearly impervious surfaces overlying dense, massive, extremely acid to very strongly alkaline, sandy to clayey materials. USDA, 1993.
slickens [minings] Accumulations of fine-textured material, such as separated in placer mining and in ore mill operations; may be detrimental to plant growth and are usually confined in specially constructed basins.
slickensides [geogenic] Vertical or oblique, roughly planar slip faces produced by external forces such as tectonics (e.g., fault), or mass movement (e.g., large slump blocks; grooves, striations on slip face; Schoeneberger and Wysocki, personal communication, 2013). Compare slickensides [pedogenic].
slide [mass movement] (a) A category of mass movement processes, associated sediments (slide deposit) or resultant landforms (e.g., rotational slide, translational slide, and snowslide) characterized by a failure of earth, snow, or rock under shear stress along one or several surfaces that are either visible or may reasonably be inferred. The moving mass may or may not be greatly deformed, and movement may be rotational (rotational slide) or planar (translational slide). A slide can result from lateral erosion, lateral pressure, weight of overlying material, accumulation of moisture, earthquakes, expansion owing to freeze-thaw of water in cracks, regional tilting, undermining, fire, and human agencies. Compare fall, topple, lateral spread, flow, complex landslide. (Schoeneberger and Wysocki, personal communication, 2013; Varnes, 1978); (b) The track of bare rock or furrowed earth left by a slide. (c) The mass of material moved in or deposited by a slide. Compare fall, flow, complex landslide, landslide (Schoeneberger and Wysocki, personal communication, 2013; Jackson, 1997).
slip face The steeply sloping surface on the lee side of a dune, standing at or near the angle of repose of loose sand, and advancing downwind by a succession of slides wherever that angle is exceeded ( Jackson, 1997).
slip surface A landslide displacement surface, often slickensided and striated, or brecciated, and subplanar. It is best exhibited in argillaceous materials and in those materials which are highly susceptible to clay alteration when granulated; also called shear surface (not preferred). Compare main scarp, landslide, escarpment(Jackson, 1997).
slipping plane Boundary of the volume of ions around a clay platelet that migrate with the platelet in an applied electrical field.
slit planting Refer to tillage, slit planting.
slope The inclination of the land surface from the horizontal; percent slope is the vertical distance divided by the horizontal distance, then multiplied by 100 (Schoeneberger and Wysocki, personal communication, 2013). Also called slope gradient or gradient.
slope alluvium Sediment gradually transported down mountain or hill slopes primarily by non-channel alluvial processes (i.e., slope wash processes) and characterized by particle sorting. Lateral particle sorting is evident on long slopes. In a profile sequence, sediments may be distinguished by differences in size and/or specific gravity of coarse fragments and may be separated by stone lines. Sorting of rounded or subrounded pebbles or cobbles and burnished peds distinguish these materials from unsorted colluvial deposits (Schoeneberger and Wyscoki, 2013; Hawley and Parsons, 1980). Compare colluvium, slope wash.
slope wash A collective term for non-fluvial, incipient alluvial processes (e.g., overland flow, minor rills) that detach, transport, and deposit sediments down hill and mountain slopes. Related sediments (slope alluvium) exhibit nominal sorting or rounding of particles, peds, etc., and lateral sorting downslope on long slopes; stratification is crude and intermittent and readily destroyed by pedoturbation and frost action. Also called slope wash processes (Schoeneberger and Wysocki, personal communication, 2013). Compare slope alluvium, colluvium, valley-side alluvium.
slot canyon A long, narrow, deep and tortuous channel or drainageway with sheer rock walls eroded into sandstone or other sedimentary rocks, especially in the semi-arid western USA (e.g., Colorado Plateau); subject to flash flood events; depth to width ratios exceed 10:1 over most of its length and can approach 100:1; commonly containing unique ecological communities distinct from the adjacent, drier uplands (Schoeneberger and Wysocki, personal communication, 2013).
slot planting Refer to tillage, slit planting.
slough (a) A small marsh, especially a marshy area lying in a local, shallow, closed depression on a piece of dry land, as on the prairie of the Midwestern USA.(b) A term used, especially in the Mississippi Valley, for a creek or sluggish body of water in a tidal flat, flood plain, or coastal marshland. Compare bayou, oxbow.(c) A sluggish channel of water, such as a side channel of a river, in which water flows slowly through low, swampy ground, as along the Columbia River, or a section of an abandoned river channel which may contain stagnant water and occurs in a flood plain or delta. (d) (not preferred) An area of soft, miry, muddy or waterlogged ground, a place of deep mud ( Jackson, 1997).
slow release A fertilizer term used interchangeably with delayed release, controlled release, controlled availability, slow acting, and metered release to designate a rate of dissolution (usually in water) much less than is obtained for completely water-soluble compounds. Slow release may involve either compounds that dissolve slowly or soluble compounds coated with substances relatively impermeable to water.
slump [mass movement] (obsolete) (a) An informal term for a mass movement process characterized by a landslide involving a shearing and rotary movement of a generally independent mass of rock or earth along a curved slip surface (concave upward) and about an axis parallel to the slope from which it descends, and by backward tilting of the mass with respect to that slope so that the slump surface often exhibits a reversed slope facing uphill ( Jackson, 1997; Schoeneberger and Wysocki, personal communication, 2013; Varnes, 1978). (b) (obsolete) The landform or mass of material slipped down during, or produced by, a slump ( Jackson, 1997; Varnes, 1978). Compare landslide.
slump block A largely intact but displaced and commonly reoriented body of rock or soil torn away as a coherent unit during a landslide (Schoeneberger and Wysocki, personal communication, 2013).
smectite
A group of 2:1 layer silicates with a high cation exchange capacity, about 110 cmolc kg-1 for soil smectites, and variable interlayer spacing. Formerly called the montmorillonite group. The group includes dioctahedral members montmorillonite, beidellite, and nontronite, and trioctahedral members saponite, hectorite, and sauconite. Compare Appendix I, Table A3.
snowfield (a) A broad expanse of terrain covered with snow, relatively smooth and uniform in appearance, occurring usually at high latitudes or in mountainous regions above the snowline and persisting throughout year. (b) A region of permanent snow cover, as at the head of a glacier; the accumulation area of a glacier. Compare glacier( Jackson, 1997).
sod planting Refer to tillage, sod planting.
sodic soil A nonsaline soil containing sufficient exchangeable sodium to adversely affect crop production and soil structure under most conditions of soil and plant type. The sodium adsorption ratio of the saturation extract is at least 13.
sodication The process whereby the exchangeable sodium content of a soil is increased.
sodium adsorption ratio (SAR) A relation between soluble sodium and soluble divalent cations that can be used to predict the exchangeable sodium fraction of soil equilibrated with a given solution. It is defined as SAR = [sodium]/[calcium + magnesium]1/2 where concentrations, denoted by brackets [ ], are expressed in mmoles per liter.
sodium adsorption ratio, adjusted
The sodium adsorption ratio of a water adjusted for the precipitation or dissolution of Ca2+ that is expected to occur where a water reacts with alkaline earth carbonates within a soil.
soil (a) The unconsolidated mineral or organic material on the immediate surface of the earth that serves as a natural medium for the growth of land plants. (b) The unconsolidated mineral or organic matter on the surface of the earth that has been subjected to and shows effects of genetic and environmental factors of: climate (including water and temperature effects), and macroand microorganisms, conditioned by relief, acting on parent material over a period of time. A product-soil differs from the material from which it is derived in many physical, chemical, biological, and morphological properties and characteristics.
soil amendment Any material such as lime, gypsum, sawdust, compost, animal manures, crop residue or synthetic soil conditioners that is worked into the soil or applied on the surface to enhance plant growth. Amendments may contain important fertilizer elements, but the term commonly refers to added materials other than those used primarily as fertilizers. Compare soil conditioner.
soil biochemistry The branch of soil science concerned with enzymes and the reactions, activities, and products of soil microorganisms.
soil conditioner A material which measurably improves specific soil physical characteristics or physical processes for a given use or as a plant growth medium; examples include sawdust, peat, compost, synthetic polymers, and various inert materials. Compare soil amendment.
soil geography The branch of physical geography that deals with the areal distributions of soils.
soil interpretations Predictions of soil behavior in response to specific uses or management based on inferences from soil characteristics and qualities (e.g., trafficability, erodibility, productivity, etc.). They are either qualitative or quantitative estimates or ratings of soil productivities, potentials, or limitations.
soil management groups Groups of taxonomic soil units with similar adaptations or management requirements for one or more specific purposes, such as: adapted crops or crop rotations, drainage practices, fertilization, forestry, highway engineering, etc.
soil moisture regimes [soil taxonomy] Refer to aquic, aridic, peraquic, torric, udic, ustic, xeric.
soil morphology (a) The physical constitution of a soil profile as exhibited by the kinds, thickness, and arrangement of the horizons in the profile, and by the texture, structure, consistence, and porosity of each horizon. (b) The visible characteristics of the soil or any of its parts.
soil organic matter The organic fraction of the soil exclusive of undecayed plant and animal residues. Compare humus.
soil sample A representative sample taken from an area, a field, or portion of a field from which the physical, biological, and chemical properties can be determined.
soil strength (cone index, penetration resistance) A transient localized soil property that is a combined measure of a given pedon’s, horizon’s, or other soil subunit’s solid phase adhesive and cohesive status. This property is most easily affected by changes in soil water content and bulk density, although other factors including texture, mineralogy, cementation, cation composition, and organic matter content also affect it. In situ characterization with soil penetrometer is the most common agricultural measure of soil strength, although measurements of other engineering components of strength on disturbed samples are also regarded as valid characterizations.
soil structure The combination or arrangement of primary soil particles into secondary units or peds. The secondary units are characterized on the basis grade (degree of distinctness), size, and type (shape; degree of distinctness). Compare soil structure grades and soil structure types (formerly called shapes).
soil aeration The condition, and sum of all processes affecting, soil pore-space gaseous composition, particularly with respect to the amount and availability of oxygen for use by soil biota and/or soil chemical oxidation reactions.
soil air The soil atmosphere; the gaseous phase of the soil, being that volume not occupied by solid or liquid.
soil association A kind of map unit used in soil surveys comprised of delineations, each of which shows the size, shape, and location of a landscape unit composed of two or more kinds of component soils or component soils and miscellaneous areas, plus allowable inclusions in either case. The individual bodies of component soils and miscellaneous areas are large enough to be delineated at the scale of 1:24,000. Several to numerous bodies of each kind of component soil or miscellaneous area are apt to occur in each delineation and they occur in a fairly repetitive and describable pattern. Compare component soil, miscellaneous areas, soil consociation, undifferentiated group.
soil auger A tool for boring into the soil and withdrawing a small sample for field or laboratory observation. Soil augers may be classified into several types as follows: (i) those with worm-type bits, uninclosed;(ii) those with worm-type bits inclosed in a hollow cylinder; and (iii) those with a hollow cylinder with a cutting edge at the lower end.
soil block An isolation volume of soil used to conduct three-dimentional flow and transport studies.
soil characteristics Soil properties that can be described or measured by field or laboratory observations, e.g., color, temperature, water content, structure, pH, and exchangeable cations.
soil chemistry The branch of soil science that deals with the chemical constitution, chemical properties, and chemical reactions of soils.
soil classification Refer to classification, soil.
soil column An isolation volume of soil used to conduct one-dimentional flow and transport studies.
soil compaction Increasing the soil bulk density, and concomitantly decreasing the soil porosity, by the application of mechanical forces to the soil.
soil complex A kind of map unit used in soil surveys comprised of delineations, each of which shows the size, shape, and location of a landscape unit composed of two or more kinds of component soils, or component soils and a miscellaneous area, plus allowable inclusions in either case. The individual bodies of component soils and miscellaneous areas are too small to be delineated at the scale of 1:24 000. Several to numerous bodies of each kind of component soil or the miscellaneous area are apt to occur in each delineation. Compare component soil, soil consociation, soil association, undifferentiated group, miscellaneous areas.
soil conservation (a) Protection of the soil against physical loss by erosion or against chemical deterioration; that is, excessive loss of fertility by either natural or artificial means. (b) A combination of all management and land use methods that safeguard the soil against depletion or deterioration by natural or by human-induced factors. (iii) The branch of soil science that deals with soil conservation (i) and (ii).
soil consociation A kind of map unit comprised of delineations, each of which shows the size, shape, and location of a landscape unit composed of one kind of component soil, or one kind of miscellaneous area, plus allowable inclusions in either case. Compare component soil, soil complex, soil association, undifferentiated group, miscellaneous areas.
soil creep Refer to creep.
soil drainage class The group in which a soil series is placed on the basis of the depth of the profile which is free from saturation.
soil extract The solution separated from a soil suspension or from a soil by filtration, centrifugation, suction, or pressure. (May or may not be heated prior to separation.)
soil fabric The combined influence of the shape, size, and spatial arrangement of soil solids and soil pores.
soil fall [mass movement] The process, associated sediments (soil fall deposit) or resultant landform characterized by a rapid type of fall involving the relatively free, downslope movement or collapse of detached, unconsolidated soil material which falls freely through the air (lacks an underlying slip face); sediments predominantly fine earth (< 2 mm); common along undercut stream banks. Also called earth fall, and (not recommended) debris fall (Schoeneberger and Wysocki, personal communication, 2013). Compare rock fall, debris fall, topple, landslide.
soil fertility The quality of a soil that enables it to provide nutrients in adequate amounts and in proper balance for the growth of specified plants or crops.
soil formation factors The variables, usually interrelated natural agencies, that are active in and responsible for the formation of soil. The factors are usually grouped into five major categories as follows: parent material, climate, organisms, topography, and time.
soil fragmentation Antonym of soil aggregation, referring to the act of breaking soil apart into fragments. Occurs mainly in response to drop shatter experiments, sieving, or tillage operations such as chisel plowing and disking.
soil genesis (a) The mode of origin of the soil with special reference to the processes or soil-forming factors responsible for development of the solum, or true soil, from unconsolidated parent material. (b) The branch of soil science that deals with soil genesis.
soil geomorphology The branch of soil science that deals with the the scientific study of the origin, distribution, and evolution of soils, landscapes and the surficial materials of which they are composed, and the processes that create them. Wysocki and Schoeneberger, 2000.
soil heat-flux density The amount of heat entering a specified cross-sectional area of soil per unit time.
soil horizon A layer of soil or soil material approximately parallel to the land surface and differing from adjacent genetically related layers in physical, chemical, and biological properties or characteristics such as color, structure, texture, consistency, kinds and number of organisms present, degree of acidity or alkalinity, etc. Compare Appendix II.
soil hydrologic cycle The fate of water from the time of precipitation until the water has been returned to the atmosphere by evaporation with particular detail given to the movement within (e.g., recharge, flowthrough) and re-emergence from (e.g., reflow, discharge) soil (Schoeneberger and Wysocki, personal communication, 2013). Refer to hydrologic cycle.
soil hydrology The science dealing with the fundamental properties and processes of water in the vadose zone.
soil hydrophobicity The tendency for a soil particle or soil mass to resist hydration, usually quantified using the water drop penetration time test. Compare soil wettability, water drop penetration time.
soil loss tolerance (T value) Refer to erosion, soil loss tolerance (T value).
soil management The combination of all tillage operations, cropping practices, fertilizer, lime, and other treatments conducted on or applied to the soil for the production of plants.
soil map A map showing the distribution of soils or other soil map units in relation to the prominent physical and cultural features of the earth’s surface. The following kinds of soil maps are recognized in the United States:
soil map, detailed Refer to soil map, detailed soil map.
soil map, detailed reconnaissance Refer to soil map, detailed reconnaissance soil map.
soil map, generalized Refer to soil map, generalized soil map.
soil map, reconnaissance Refer to soil map, reconnaissance soil map.
soil map, schematic Refer to soil map, schematic soil map.
soil matrix The solid phase constituents of the soil. Often used to refer to the soil pore system within aggregates.
soil mechanics and engineering The branches of engineering and soil science that deal with the effect of forces on the soil and the application of engineering principles to problems involving the soil.
soil microbial diversity Expression of the variety of soil microorganisms and activities at the genetic, species, and soil ecosystem levels; measurements based on communities rather than species.
soil microbiology The branch of soil science concerned with soil-inhabiting microorganisms, their functions, and activities.
soil micromorphology The study of soil morphology by microscopic (light optical and less frequently by submicroscopic) methods, often using thin-section techniques.
soil mineral (a) Any mineral that occurs as a part of or in the soil. (b) A natural inorganic compound with definite physical, chemical, and crystalline properties (within the limits of isomorphism) that occurs in the soil. Compare clay mineral.
soil mineralogy The branch of soil science that deals with the homogeneous inorganic materials found in the earth’s crust to the depth of weathering or of sedimentation.
soil monolith A vertical section of a soil profile removed from the soil and mounted for display or study.
soil order [soil taxonomy] A group of soils in the broadest classification category. For example, in the 1938 U.S. classification system (Baldwin, et al.; 1938), the three soil orders were zonal soil, intrazonal soil, and azonal soil. In the soil taxonomy (1975), there were originally 10 soil orders. In the current soil taxonomy (USDA, 1999) there are 12 soil orders, differentiated by the presence or absence of diagnostic horizons and consist of: Alfisols, Andisols, Aridisols, Entisols, Gelisols, Histosols, Inceptisols, Mollisols, Oxisols, Spodosols, Ultisols, Vertisols. Orders are divided into suborders and the Suborders are further divided into great groups (USDA, 1999).
soil organic residue Animal and vegetative materials added to the soil of recognizable origin.
soil oxygen diffusion rate (a) The rate of diffusion of oxygen through soil as defined by Fick’s law. (b) A measurement of diffusion governed oxygen reduction rate at the surface of platinum microelectrodes used to assess the oxygen supplying ability of the soil relative to the needs of plant roots, usually referred to as soil ODR.
soil physics The branch of soil science that deals with the physical properties of the soil, with emphasis on the state and transport of matter (especially water) and energy in the soil.
soil piping Accelerated erosion that results in subterranean voids and tunnels. Also called soil tunneling.
soil population (a) All the organisms living in the soil, including plants and animals. (b) Members of the same taxa. (iii) Delineations of the same map unit—a grouping of like things in a statistical sense.
soil pores That part of the bulk volume of soil not occupied by soil particles. Soil pores have also been referred to as interstices or voids.
soil productivity The capacity of a soil to produce a certain yield of crops or other plants with a specified system of management.
soil qualities Inherent attributes of soils that are inferred from soil characteristics or indirect observations (e.g., compactibility, erodibility, and fertility).
soil quality The capacity of a soil to function within ecosystem boundaries to sustain biological productivity, maintain environmental quality, and promote plant and animal health.
soil ripples (not recommended) Use terracettes.
soil science That science dealing with soils as a natural resource on the surface of the earth including soil formation, classification, and mapping; physical, chemical, biological, and fertility properties of soils per se; and these properties in relation to the use and management of soils.
soil separates Mineral particles, <2.0 mm in equivalent diameter, ranging between specified size limits. The names and size limits of separates (classes) recognized in the United States are: very coarse sand (prior to 1947 this separate was called “fine gravel;” now fine gravel includes particles between 2.0 mm and about 12.5 mm in diameter), 2.0 to 1.0 mm; coarse sand, 1.0 to 0.5 mm; mediumsand, 0.5 to 0.25 mm; fine sand, 0.25 to 0.10 mm; veryfine sand, 0.10 to 0.05 mm; silt, 0.05 to 0.002 mm; and clay (prior to 1937, “clay” included particles <0.005 mm in diameter, and “silt,” those particles from 0.05 to 0.005mm) <0.002 mm. The separates (classes) recognized by the International Society of Soil Science are: (i) coarse sand, 2.0 to 0.2 mm; (ii) fine sand, 0.2 to 0.02 mm; (iii) silt, 0.02 to 0.002 mm; and (iv) clay, <0.002 mm.
soil series The lowest category in the U.S. system of soil taxonomy; a conceptualized class of soil bodies (polypedons) that have limits and ranges more restrictive than all higher taxa. Soil series are commonly used to name dominant or codominant polypedons represented on detailed soil maps. The soil series serve as a major vehicle to transfer soil information and research knowledge from one soil area to another. (USDA, 1999)
soil solution The aqueous liquid phase of the soil and its solutes and its solutes.
soil structure grades
A grouping or classification of soil structure on the basis of interand intra-aggregate adhesion, cohesion, or stability. Four grades of structure are recognized as follows:structureless No observable aggregation or no definite and orderly arrangement of natural lines of weakness. There are two end-members (subsets) of structureless soil structure: Massive, if a coherent mass which may or may not be cemented (e.g., highly weathered bedrock); or single-grain, if noncoherent (e.g., loose sand).weak Poorly formed indistinct peds, barely observable in place. When gently disturbed, the soil material parts into a mixture of whole and broken units and much material that exhibits no planes of weakness. moderate Well-formed distinct peds evident in undisturbed soil. When disturbed, soil material parts into a mixture of whole units, broken units, and material that is not in units.strong Peds are distinct in undisturbed soil. They separate cleanly when soil is disturbed, and the soil material separates mainly into whole units when removed.
soil structure shapes Refer to soil structure types.
soil structure sizes Refer to soil structure and Table 5.
soil structure types A classification of soil structure based on the shape of the aggregates or peds in the profile. Compare soil structure and Table 5.
soil surface seal Refer to surface sealing.
soil survey (a) The systematic examination, description, classification, and mapping of soils in an area. Soil surveys are classified according to the kind and intensity of field examination. (b) The program of the National Cooperative Soil Survey (colloquial–USA) that includes developing and implementing standards for describing, classifying, mapping, writing, and publishing information about soils of a specific area.
soil taxonomy The present-day U.S. Department of Agriculture soil classification system (USDA, 1999; Appendix 1).
soil temperature regimes Refer to cryic, frigid, hyperthermic, mesic, pergelic, thermic.
soil test A chemical, physical, or biological procedure that estimates the suitability of the soil to support plant growth. (Sometimes used as an adjective to define fractions of soil components, e.g., “soil test phosphorus.”)
soil test calibration The process of determining the crop nutrient requirement at different soil test values.
soil test correlation The process of determining the relationship between plant nutrient uptake or yield and the amount of nutrient extracted by a particular soil test method.
soil test critical concentration The concentration of an extractable nutrient above which a crop response to added nutrient would not be expected.
soil test interpretation The process of developing nutrient application recommendations from soil test concentration, and other soil, crop, economic, environmental, and climatic information.
soil texture
The relative proportions of the various soil separates in a soil as described by the classes of soil texture shown in Fig. 1. The textural classes may be modified by the addition of suitable adjectives when rock fragments are present in substantial amounts; for example, “stony silt loam.” (For other modifiers Compare rock fragments.) The sand, loamy sand, and sandy loam are further subdivided on the basis of the proportions of the various sand separates present. The limits of the various classes and subclasses are as follows:clay Soil material that contains 40% or more clay,<45% sand, and <40% silt.clay loam Soil material that contains 27 to 40% clay and 20 to 45% sand.loam Soil material that contains 7 to 27% clay, 28 to 50% silt, and <52% sand.loamy sand Soil material that contains between 70 and 91% sand and the percentage of silt plus 1.5 times the percentage of clay is 15 or more; and the percentage of silt plus twice the percentage of clay
soil type [soil taxonomy] (a) (obsolete) Prior to soil taxonomy (USDA, 1975) The lowest unit in the natural system of soil classification; a subdivision of a soil series and consisting of or describing soils that are alike in all characteristics including the texture of the A horizon or plow layer; (b) In Europe, roughly equivalent to a great soil group. Compare soil series.
soil variant [soil taxonomy] (obselete) A soil whose properties are believed to be sufficiently different from other known soils to justify a new series name but comprising such a limited geographic area that creation of a new series is not justified. Use of this term was discontinued in 1988. Compare taxadjunct.
soil water Please refer to the specific soil water terms listed below and Table 1:
soil water characteristic The relationship between the soil-water content (by mass or volume) and the soil-water matric potential. Also called the water retention curve or isotherm, and the water release curve.
soil water diffusivity The hydraulic conductivity divided by the differential water capacity (care being taken to be consistent with units), or the flux of water per unit gradient of water content in the absence of other force fields.
soil water pressure Refer to soil water, soil water potential.
soil welding A process in which pedogenesis in a surface layer of parent rock or sediment feeds physicochemical and other imprints downward into a subjacent buried soil formed in a separate parent rock or sediment, leading to pedogenic “fusion” of the two soils. Refer to pedogenic overprinting or pedogenic imprinting.
soil wettability Refer to soil hydrophobicity, water drop penetration time.
soil-moisture tension Refer to soil water, soil water potential.
solid set sprinkler irrigation Refer to irrigation, sprinkler irrigation systems terms, solid set.
solifluction Slow, viscous downslope flow of water-saturated regolith. Rates of flow vary widely. The presence of frozen substrate or even freezing and thawing is not implied in the original definition. However, one component of solifluction can be creep of frozen ground. The term is commonly applied to processes operating in both seasonal frost and permafrost areas. Compare creep (National Research Council of Canada, 1988).
solifluction deposit A deposit of non-sorted, water-saturated, earthy material locally derived that is moving or has moved down slope en masse, caused by the melting of seasonal frost or permafrost, resulting in an over-thickened leading edge of linera, lobate, or irregular forms that loosely parallele or obliquely follow the slope contour; may be surficially armored by coarse fragments on the leading margin (Schoeneberger and Wysocki, personal communication, 2013).
solifluction lobe An isolated tongue-shaped feature up to 25 m wide and 150 m or more long, formed by rapid solifluction on certain sections of a slope showing variations in gradient. This feature commonly has a steep (e.g., 15°–60°) front and a relatively smooth upper surface (National Research Council of Canada, 1988).
solifluction sheet A broad deposit of nonsorted, water-saturated, locally derived material that is moving or has moved downslope, en masse. Stripes are commonly associated with solifluction sheets (National Research Council of Canada, 1988). Compare stripe.
solifluction terrace A low step with a straight or lobate front, the latter reflecting local differences in rate of flow. A solifluction terrace may have bare mineral soil on the upslope part and ‘folded under’ organic matter in both the seasonally thawed and the frozen soil (National Research Council of Canada, 1988).
Solonchak [soil classification] (obsolete; not used in soil taxonomy) A great soil group of the intrazonal order and halomorphic suborder, consisting of soils with gray, thin, salty crust on the surface, and with fine granular mulch immediately below being underlain with grayish, friable, salty soil; formed under subhumid to arid, hot or cool climate, under conditions of poor drainage, and under a sparse growth of halophytic grasses, shrubs, and some trees (Baldwin et al., 1938).
Solonetz [soil classification] (obsolete; not used in soil taxonomy) A great soil group of the intrazonal order and halomorphic suborder, consisting of soils with a very thin, friable, surface soil underlain by a dark, hard columnar layer usually highly alkaline; formed under subhumid to arid, hot to cool climates, under better drainage than Solonchaks, and under a native vegetation of halophytic plants (Baldwin, et al.; 1938).
solum (plural: sola) A set of horizons that are related through the same cycle of pedogenic processes; the A, E, and B horizons.
solution corridor A straight, open trench about 3 to 10 m wide in a karst area, formed by vertical and lateral solution zones developed along bedrock fractures; also called (not preferred) bogaz, zanjon (Puerto Rico; Schoeneberger and Wysocki, personal communication, 2013; Jackson, 1997). Compare cutter, solution fissure, karst valley.
solution fissure One of a series of vertical open cracks commonly < 0.5 m wide dissolved along joints or fractures, separating limestone pavement (pavement karst) into blocks (clints); also called kluftkarren (not preferred; Schoeneberger and Wysocki, personal communication, 2013; Jackson, 1997; White, 1988). Compare cutter, solution corridor, karren.
solution pipe A subsurface, vertical, cylindrical or cone-shaped hole, formed by dissolution in soluble bedrock (e.g., limestone) and often without surface expression, that is filled with detrital material (e.g., soil) and which serves as a bypass route for internal water flow (Schoeneberger and Wysocki, personal communication, 2013; Jackson, 1997).
solution sinkhole The most common type of sinkhole, caused by dissolution that forms fissures or a chimney and a depression in the bedrock surface which grows when closely spaced fissures underneath it enlarge and coalesce (Schoeneberger and Wysocki, personal communication, 2013, White, 1988; Jackson, 1997). Compare collapse sinkhole.
solution valley (not preferred) Use karst valley.
sombric horizon [soil taxonomy] A diagnostic subsurface mineral horizon that is darker in color than the overlying horizon but that lacks the properties of a spodic horizon. Common in cool, moist soils of high altitude in tropical regions.
somewhat poorly drained A soil drainage class referring to soils which have evidence of seasonal water tables at depths between 20 and 46 cm (8 and 18 in).
sorption
The removal of an ion or molecule from solution by adsorption and absorption. It is often used when the exact nature of the mechanism of removal is not known.
sorptivity
S = It-1/2 for horizontal infiltration of water, where I is cumulative infiltration and t is time. Sorptivity is dependent on initial and boundary conditions of soil water content among other factors.
sorted circle A type of patterned ground whose mesh (shape) is largely circular and has a sorted appearance commonly due to a border of coarse fragments surrounding finer material, occurring either singly or in groups. Diameters range from a few centimeters to more than 10 m. The coarse fragment border may be 35 cm high and 8 to 12 cm wide ( Jackson, 1997; National Research Council of Canada, 1988). Compare patterned ground.
sorted polygon Use patterned ground.
sound [coast] (a) A relatively long, narrow waterway connecting two larger bodies of water (as a sea or lake with the ocean or another sea) or two parts of the same water body, or an arm of the sea forming a channel between the mainland and an island (e.g., Puget Sound, WA); it is generally wider and more extensive than a strait [coast]. (b) A long, large, rather broad inlet of the ocean, generally extending parallel to the coast (e.g., Long Island Sound, NY). (c) A lagoon along the southeast coast of the U.S.A. (e.g., Pamlico Sound, NC). (d) A long bay or arm of a lake; a stretch of water between the mainland and a long island in a lake. Compare sound, lagoon, gulf, ocean ( Jackson, 1997).
spatial variability The variation in soil properties (i) laterally across the landscape, or (ii) vertically downward through the soil.
spatter cone A small, steep-sided cone (e.g., 3–15 m high, or more) built up on a lava flow, usually pahoehoe, composed of clots of lava ejected with escaping gases from a vent or fissure which spatters and congeals as it hits the ground to form a small cone; rougher lava clots than a spiracle (Schoeneberger and Wysocki, personal communication, 2013). Compare spiracle.
specific activity Number of enzyme activity units per mass of protein. Often expressed as micromoles of product formed per unit time per milligram of protein. Also used in radiochemistry to express the radioactivity per mass of material (radioactive + nonradioactive).
specific adsorption The strong adsorption of ions or molecules on a surface. Specifically adsorbed materials are not readily removed by ion exchange.
specific gravity The ratio of a material’s density to that of water [material weight in air ¸ (weight in air weight in water)]. Used to differentiate different kinds of volcaniclastics and other materials (Schoeneberger and Wysocki, personal communication, 2013).
specific surface
The solid-particle surface area (of a soil or porous medium) divided by the solid-particle mass or volume, expressed in m2 kg-1or m2 m-3 = m-1, respectively.
specific water capacity The change of soil-water mass content with change in soil-water matric potential.
specific yield The water storage term for an unconfined aquifer. Defined as the volume of water released from an unconfined aquifer per unit surface area of the aquifer surface area per unit drop in the water table depth.
spiracle [volcanic] A small tubular opening or chimney formed by fluid lava congealing and mounding around a fumarolic vent in a basaltic lava flow, usually about 1 m in diameter and up to 5 m high, although in the northwestern USA where spiracles are common they generally are 10 m in diameter and 12 m high or more; formed by a gaseous explosion in lava that is still fluid, probably due to steam generated from underlying wet material; smoother lava clots and drapes than a spatter cone (Schoeneberger and Wysocki, personal communication, 2013; Green and Short, 1971; Jackson, 1997). Compare spatter cone.
spit (a) A small point or low tongue or narrow embankment of land, commonly consisting of sand or gravel deposited by longshore transport and having one end attached to the mainland and the other terminating in open water, usually the sea; a finger-like extension of the beach. (b) A relatively long, narrow shoal or reef extending from the shore into a body of water ( Jackson, 1997).
splash erosion Refer to erosion, splash erosion.
splay (not preferred) Use flood-plain splay.
spodic horizon [soil taxonomy] A diagnostic, subsurface mineral soil horizon that is characterized by the illuvial accumulation of amorphous materials composed of aluminum and organic carbon with or without iron. The spodic horizon has a certain minimum thickness, and a minimum quantity of extractable carbon plus iron plus aluminum in relation to its content of clay. (USDA, 1999).
Spodosols [soil taxonomy] An order of mineral soils that have a spodic horizon (amorphous mixtures of organic matter and aluminum, with or without iron accumulations) or a placic horizon that overlies a fragipan or another sequum that has an argillic horizon. Spodosols commonly have a udic soil moisture regime, but may have a xeric regime or aquic conditions, and may have any soil temperature regime (USDA, 1999; Appendix 1).
spoil bank A bank, mound, or other artificial accumulation of rock debris, and earthy dump deposits removed from ditches strip mines, or other excavations (Schoeneberger and Wysocki, personal communication, 2013). Compare dredge spoil bank.
spoil pile (a) A bank, mound, or other artificial accumulation composed of spoil; e.g., an embankment of earthy material removed from a ditch and deposited alongside it. Compare dredge spoil bank. (b) A pile of refuse material from an excavation or mining operation; e.g., a pile of dirt removed from, and stacked at the surface of a mine in a conical heap or in layers (Schoeneberger and Wysocki, personal communication, 2013; Jackson, 1997).
sporadic permafrost The area near the southern boundary of discontinuous permafrost where permafrost occurs in isolated patches or islands (National Research Council of Canada, 1988). Compare continuous permafrost, discontinuous permafrost.
spores Specialized reproductive cell. Asexual spores germinate without uniting with other cells, whereas sexual spores of opposite mating types unite to form a zygote before germination occurs.
spray irrigation Refer to irrigation, spray irrigation.
spread Use lateral spread
sprinkler Refer to irrigation, sprinkler.
spur [geomorphology] A subordinate ridge or lesser elevation that projects sharply from the crest or side of a hill, mountain, or other prominent range of hills or mountains ( Jackson, 1997).
spur ridge (not recommended) use spur.
stack [coast] An isolated pillar-like rocky island or mass near a cliffy shore, detached from a headland by wave erosion assisted by weathering; especially one showing columnar structure with horizontal stratification. Examples occur along the Oregon coast and the Lake Superior shore (Schoeneberger and Wysocki, personal communication, 2013; Jackson, 1997).
stagnant ice (a) Glacial ice that is not flowing forward and is not receiving material from an accumulation area; (b) Detached blocks of ice left behind by a retreating glacier, usually buried in a moraine and melting very slowly ( Jackson, 1997).
standard cone (ASAE standard cone) The coneshaped tip used at the insertion end of soil penetrometer probes, following design criteria prescribed by the ASAE standard. Briefly, a 30 degree stainless steel cone having a basal diameter of either 20.27 or 12.83 mm.
star dune A large, isolated sand dune whose base, in plan view, resembles a star, with sharp-crested ridges converging from basal points to a central peak that may be as high as 100 m above the surrounding plain. It tends to remain fixed for centuries in an area where the wind blows from all directions. Compare dune ( Jackson, 1997).
State Physiographic Area An area of relatively local extent and whose parts are similar in geologic structure and climate and which has consequently had a unified geomorphic history, and whose pattern of relief or landforms differ significantly from that of adjacent areas; that is, a subset within a Physiographic Section (Schoeneberger and Wysocki, personal communication, 2013).
static penetrometer A penetrometer that is pushed into the soil at a constant and slow rate of penetration.
stem flow The movement of water (precipitation ro irrigation) down stems and branches of plants.
steptoe An island-like area of older rock surrounded by a lava flow (Hawley and Parsons, 1980). Compare kipuka.
sterilization Rendering an object or substance free of viable microbes.
Stern layer A layer of positive ions held so tightly to the clay surface that they migrate with the clay in an electrical field.
sticky point
(a) A condition of consistency at which the soil barely fails to stick to a foreign object. (b) Specifically and numerically, the water mass content of a well-mixed kneaded soil that barely fails to adhere to a polished nickel or stainless steel surface when the shearing speed is 50 mm s-1.
stock
A relatively small, concordant and/or discordant plutonic rock body exposed at the land surface, with an aerial extent < 40 sq. mi. (100 km2) and no known bottom (Jackson, 1997). Compare batholith.
Stokes’ law
The equation expressing the force of viscous resistance on a smooth, rigid sphere moving in a viscous fluid under standard temperature and pressure, namelyF=3πηDVwhere F is the force of viscous resistance, π = 3.1416, η is the fluid viscosity, D is the diameter of the sphere, and V is the velocity of fall (or movement). Applying Stokes’ law to gravity sedimentation as used in particle-size analysis of soil by pipette or hydrometer methods, the resulting sedimentation equation isV=2gr2(d1– d2)/9ηwhere g is the acceleration of gravity, r is the “equivalent” radius of a particle, d1 is the soil-particle density, and d2 is the fluid density. Stokes’ law applied to centrifugation yields still another equation for V.
stone line A sheet-like lag concentration of coarse fragments in surficial sediments. In cross section, the line may be marked only by scattered fragments or it may be a discrete layer of fragments. The fragments are more often gravels or cobbles than stones. A stone line generally overlies material that was subject to weathering, soil formation, and erosion before deposition of the overlying material. Many stone lines seem to represent buried erosion pavements, originally formed by running water on the land surface and concurrently covered by surficial sediment. Also called a carpedolith. Compare erosional pavement, desert pavement.
stone net (not preferred) use patterned ground. Synonym sorted polygon, stone polygon.
stones Rock or mineral fragments ≥250 to 600 mm in diameter if rounded, and 380 to 600 mm if flat. Compare rock fragments.
stoniness Classes based on the relative proportion of stones at or near the soil surface. Used as a phase distinction in mapping soils. Compare rock fragments.
stony (a) A stoniness class in which there are enough stones at or near the soil surface to be a continuing nuisance during operations that mix the surface layer, but they do not make most such operations impractical. (b) Containing appreciable quantities of stones. Compare rock fragments.
storativity The storage term for a confined aquifer. Defined as the volume of water released from a confined aquifer per unit surface area of the aquifer and per unit drop in the hydraulic head.
storm surge An abnormal, sudden rise of sea level along an open coast during a storm, caused primarily by onshore-wind stresses, or less frequently by atmospheric pressure reduction, resulting in water piled up against the coast. It is most severe when accompanied by a high tide ( Jackson, 1997).
stormflow The hydrologic response of a watershed to storm events. Often used to refer strictly to subsurface flow through the shallow zone of hillslopes during storm events.
stoss (adjective) Said of the side of the hill or knob that faces the direction from which an advancing glacier or ice-sheet moved; facing the upstream (“up-ice”) side of a glacier, and most exposed to its abrasive action ( Jackson, 1997). Compare lee, stoss and lee, crag and tail.
stoss and lee An arrangement of small hills or prominent rocks, in a strongly glaciated area, having gentle slopes on the stoss (“up-ice”) side and somewhat steeper, plucked slopes on the lee (“down-ice”) side. This arrangement is the opposite of crag and tail ( Jackson, 1997). Compare crag and tail, drumlin, drumlinoid ridge, flute.
strait
[coast] A relatively narrow waterway connecting two larger bodies of water, as the Straits of Mackinac linking Lake Michigan and Lake Huron; a large channel (Jackson, 1997). Compare sound.
strand plain A prograded shore built seaward by waves and currents, and continuous for some distance along the coast. It is characterized by subparallel beach ridges and swales, in places with associated dunes ( Jackson, 1997).
strandline
(a) The shoreline, especially a former (relict) shoreline now elevated above the present water level, that commonly appears as a bench or line wrapping around the landscape at a common elevation (Schoeneberger and Wysocki, personal communication, 2013).(b) A beach, especially one raised above the present sea or lake level (Jackson, 1997).
strath terrace A type of stream terrace, formed as an erosional surface cut on bedrock and thinly mantled with stream deposits (alluvium), commonly with a gravel lag deposit immediately above the bedrock (Schoeneberger and Wysocki, personal communication, 2013; Jackson, 1997).
stratified (adjective) Formed, arranged in or composed of strata or layers. The term refers to geologic deposits. Layers in soils that result from the processes of soil formation are called horizons; those inherited from the parent material are called strata (Schoeneberger and Wysocki, personal communication, 2013).
stratovolcano A volcano that is constructed of alternating layers of lava and pyroclastic deposits, along with abundant dikes and sills. Viscous, acidic lava may flow from fissures radiating from a central vent, from which pyroclastics are ejected ( Jackson, 1997). Compare shield volcano.
straw mulching The use of straw to create a surface mulch on all or part of the soil surface for soil or water conservation, for soil temperature management or for weed suppression. Compare erosion, furrow mulching; tillage, stubble mulch.
stream (a) Any body of running water that moves under gravity to progressively lower levels, in a relatively narrow but clearly defined channel on the ground surface, in a subterranean cavern, or beneath or in a glacier. It is a mixture of water and dissolved, suspended, or entrained matter. (b) A term used in quantitative geomorphology interchangeably with channel ( Jackson, 1997). Compare river.
stream channel (not preferred) Use channel.
stream order An integer system applied to tributaries (stream segments) that documents their relative position within a drainage basin network as determined by the pattern of its confluences. The order of the drainage basin is determined by the highest integer. Several systems exist. In the Strahler system, the smallest unbranched tributaries are designated Order 1; the confluence of two first-order streams produces a stream segment of Order 2; the junction of two second-order streams produces a stream segment of Order 3, etc.
stream terrace One of a series of flat-topped landforms in a stream valley, that flank and are parallel to the stream channel, originally formed by a previous stream level, and representing the dissected remnants of an abandoned flood plain, stream bed, or valley floor produced during a past state of erosion or deposition (i.e., currently it very rarely or never floods; inactive cut and fill and/or scour and fill processes). Erosional surfaces cut into bedrock and thinly mantled with stream deposits (alluvium) are designated “strath terraces.” Remnants of constructional valley floors thickly mantled with alluvium are termed alluvial terraces (Schoeneberger and Wysocki, personal communication, 2013; Hawley and Parsons, 1980). Compare alluvial terrace, flood-plain step, strath terrace, terrace.
streamflow The net flow of water through a stream channel that integrates all contributing components, e.g., overland flow, interflow, and groundwater discharge.
streamline The flow path of a water molecule in the soil.
strike valley A subsequent valley eroded in, and developed parallel to the strike of, underlying weak strata, such as a cuesta; a valley that commonly, but not necessarily, contains a subsequent stream (Schoeneberger and Wysocki, personal communication, 2013; Jackson, 1997).
string bog A peatland with roughly parallel, narrow ridges of peat dominated by peat vegetation interspersed with slight depressions, many of which contain shallow pools. The ridges are at right angles to low (< 2°) slopes. They are typically 1 to 3 m wide, up to 1 m high and may be over 1 km long. The ridges are slightly elevated and are better drained allowing shrubs and trees to grow. They are best developed in areas of discontinuous permafrost (National Research Council of Canada, 1988).
strip cropping Refer to tillage, strip cropping.
strip planting Refer to tillage, strip planting.
strip till planting Refer to tillage, strip till planting.
stripe A type of patterned ground; one of the alternating bands of fine and coarse surface material, or of rock or soil and vegetation-covered ground, commonly found on steeper slopes. It is usually straight, but may be sinuous or branching. Compare patterned ground ( Jackson, 1997).
structural back slope (not recommended) use dip slope.
structural bench A shelf or step-like landform produced or controlled by erosion resistant, horizontally-bedded rock. Erosion removes overlying weaker rock or sediment forming a nearly level to gently inclined surface that rests on a relatively resistant strata or rock that ascends to a higher slope or platform. Structural benches may occur as a single feature or as a series of stepped-surfaces where alternating weak and resistant strata exist. Due to erosion resistance, structural benches may have little or no geomorphic implication regarding fluvial deposition, past erosion cycles or former stream, basin, or base levels (Schoeneberger and Wysocki, personal communication, 2013). Compare mesa, pediment, ledge, scarp.
structural charge The charge (usually negative) on a mineral resulting from isomorphous substitution within the mineral layer. (Expressed as moles [mol] or centimoles [cmol] of charge per kilogram of clay.)
structural diversity Microbial community description based on composition of different taxa and DNA/ RNA sequence types.
structure Refer to crystal structure, soil structure.
stubble mulch Refer to tillage, stubble mulch.
subaerial (adjective) Said of conditions and processes, such as erosion, that exist or operate in the open air on or immediately adjacent to the land surface; or of features and materials, such as eolian deposits, that are formed or situated on the land surface ( Jackson, 1997). Compare subaqueous.
subaqueous (adjective) Said of conditions, processes, features or deposits that exist or operate in or under water (Subaqueous Soil Subcommittee, 2005; Jackson, 1997). Compare subaerial.
subaqueous landscapes Permanently submerged areas that are fundamentally the same as subaerial (terrestrial) systems in that they have a discernable topography composed of mappable, subaqueous landforms. (Subaqueous Soil Subcommittee, 2005).
subaqueous soils Soils that form in sediment found in shallow, permanently flooded environments. 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 Soil Subcommittee, 2005).
Subarctic Brown Forest soils [soil classification] (obsolete; not used in soil taxonomy) Soils similar to Brown Forest soils except having more shallow sola and average temperatures of <5°C at 46 m (18 in) or more below the surface (Kellogg and Nygard, 1951).
subbing Refer to irrigation, subbing.
subglacial (adjective) (a) Formed or accumulated in or by the bottom parts of a glacier or ice sheet; said of meltwater streams, till, moraine, etc. (b) Pertaining to the area immediately beneath a glacier, as subglacial eruption or subglacial drainage ( Jackson, 1997).
subglacial melt-out till (not preferred) use meltout till.
subglacial till Till deposited beneath, in or by the bottom parts of a glacier or ice sheet; subglacial till types include lodgment till, subglacial flow till and subglacial melt-out till. (Schoeneberger and Wysocki, personal communication, 2013; Goldthwaite and Matsche, 1988).
subglacial flow till (not preferred) use flow till.
submerged back-barrier beach A permanently submerged extension of the back-barrier beach that generally parallels the boundary between estuary and the barrier island (Subaqueous Soil Subcommittee, 2005). Compare submerged mainland beach, barrier beach.
submerged mainland beach A permanently submerged extension of the mainland beach that generally parallels the boundary between an estuary or lagoon and the mainland (Subaqueous Soil Subcommittee, 2005). Compare submerged back-barrier beach, barrier beach.
submerged wave-built terrace A subaqueous, relict depositional landform originally constructed by river or longshore sediment deposits along the outer edge of a wave-cut platform and later submerged by rising sea level or subsiding land surface ( Jackson, 1997).
submerged wave-cut platform A subaqueous,relict erosional landform that originally formed as a wave-cut bench and abrasion platform from coastal wave erosion and later submerged by rising sea level or subsiding land surface ( Jackson, 1997). Comparewave-built terrace, wave-cut platform.
submerged point bar [coastal] The submerged extension of an exposed (subaerial) point bar (Subaqueous Soil Subcommittee, 2005).
submerged-upland soil Mineral or organic soil that primarily formed in a subaerial setting but is now under water, commonly in intertidal or subaqueous settings. Inundation could occur for various reasons (e.g., sea-level rise in a marine or estuarine system, or ponding from a dam). In intertidal settings, tidal marsh soils may occur above former subaerial soils (refer to submerged-upland tidal marsh). In subaqueous settings (permanently submerged), submerged-upland soils typically occur beneath a cap of subaqueous soil forming in the current underwater environment (Schoeneberger and Wysocki, personal communication, 2013).
submerged-upland tidal marsh An extensive tract of land that is alternately covered and uncovered by the tide, and nearly level, intertidal landform composed of unconsolidated sediments (clays, silts, and/or sand and organic materials), a resistant root mat, vegetated dominantly by hydrophytic (water loving) plants. The mineral sediments largely retain pedogenic horizonation and morphology (e.g., argillic horizons) developed under better drained, terrestrial subaerial conditions prior to submergence due to sea level rise; a type of tidal marsh (Schoeneberger and Wysocki, personal communication, 2013). Compare tidal marsh.
subsoiling Refer to tillage, subsoiling.
substrate (a) That which is laid or spread under an underlying layer, such as the subsoil. (b) The substance, base, or nutrient on which an organism grows.(c) Compounds or substances that are acted upon by enzymes or catalysts and changed to other compounds in the chemical reaction.
substrate utilization patterns (phenotyping) The metabolic potential of soil microbial communities based on the number of substrates used that differentiate the microbial community.
substratum Any layer lying beneath the soil solum, either conforming or unconforming.
subsurface tillage Refer to tillage, subsurface tillage.
subtidal (adjective) Continuous submergence of substrate in an estuarine or marine ecosystem; these areas are below the mean low tide (Subaqueous Soil Subcommittee, 2005; CC). Compare intertidal.
subtidal wetlands Permanently inundated areas within estuaries dominated by subaqueous soils and submerged aquatic vegetation (Subaqueous Soil Subcommittee, 2005).
sulfidic material
Waterlogged material or organic material that contains 7.5 g kg-1 or more of sulfide-sulfur.
sulfur cycle The sequence of transformations undergone by sulfur wherein it is used by living organisms, transformed upon death and decomposition of the organism, and ultimately converted to its original oxidation state.
sulfuric horizon [soil taxonomy] A diagnostic, subsurface horizon composed either of mineral or organic soil material that has both pH <3.5 and jarosite mottles (USDA, 1999).
summation curve, particle size A curve showing the accumulative percentage by mass of particles within increasing (or decreasing) size limits as a function of diameter; the percent by mass of each size fraction is plotted accumulatively on the ordinate as a function of the total range of diameters represented in the sample plotted on the abscissa.
summer fallow Refer to tillage, summer fallow.
summit A general term for the highest point of any landform remanant, hill, or mountain.
superglacial (not recommended) Use supraglacial.
superphosphate
A product obtained when phosphate rock is treated with H2SO4 , H2PO4, or a mixture of those acids.
superphosphoric acid The acid form of polyphosphates, consisting of a mixture of orthophosphoric and polyphosphoric acids. Species distribution varies with concentration, which is typically 30 to 36% P (68 to 83% P2O5).
supraglacial (adjective) Carried upon, deposited from, or pertaining to the top surface of a glacier or ice sheet; said of meltwater streams, till, drift, etc. ( Jackson, 1997).
supraglacial debris-flow sediment (not preferred) Use flow till.
supraglacial flow till (not preferred) Uuse flow till.
supraglacial melt-out till (not preferred) Use meltout till.
supraglacial till Till deposited on top of or within the upper part of a glacier or ice sheet. Melting of glacial ice deposits supraglacial till atop subjacent material, which forms topographic highs on a resultant landscape. Supraglacial till types include supraglacial flow till and supraglacial melt-out till (Schoeneberger and Wysocki, personal communication, 2013; Goldthwaite and Matsche, 1988). Compare till, subglacial till.
surface area
The area of the solid particles in a given quantity of soil or porous medium. (a) BET surface area is that area on which gas molecules, such as N2 or O2, can adsorb, which normally does not include the planar surface of expanding clays such as smectites. (b) EGME surface area is that area on which ethylene glycol monoethyl ether can adsorb, which normally includes the planar surface of expanding clays such as smectites. Compare specific surface.
surface creep Refer to erosion, surface creep.
surface mine A depression, open to the sky, resulting from the surface extraction of earthy material (e.g., soil/ fill) or bedrock material (e.g., coal; Schoeneberger and Wysocki, personal communication, 2013). Compare borrow pit, openpit mine, quarry.
surface runoff Refer to runoff.
surface sealing The deposition by water, orientation, and/or packing of a thin layer of fine soil particles on the immediate surface of the soil, greatly reducing its water permeability.
surface soil The uppermost part of the soil, ordinarily moved in tillage, or its equivalent in uncultivated soils and ranging in depth from 7 to 25 cm. Frequently designated as the plow layer, the surface layer, the Ap layer, or the Ap horizon. Compare topsoil.
surface tension The amount of energy required to create a new water surface.
surface-charge density The excess of negative or positive charge per unit of surface area of soil or soil mineral.
surfactant A substance that lowers the surface tension of a liquid.
surge irrigation Refer to irrigation.
suspension The state in which particles of a solid are mixed with a fluid but are not dissolved.
sustainability Managing soil and crop cultural practices so as not to degrade or impair environmental quality on or off site, and without eventually reducing yield potential as a result of the chosen practice through exhaustion of either on-site resources or nonrenewable inputs.
swale (a) A shallow, open depression in unconsolidated materials which lacks a defined channel but can funnel overland or subsurface flow into a drainageway. Soils in swales tend to be moist and thicker (cumulic) compared to surrounding soils (Schoeneberger and Wysocki, personal communication, 2013). (b) A small, shallow, typically closed depression in an undulating ground moraine formed by uneven glacial deposition; Compare swell-and-swale topography. (c) (not preferred; use interdune) A long, narrow, generally shallow, trough-like depression between two beach ridges, and aligned roughly parallel to the coastline ( Jackson, 1997).
swallow hole A closed depression or doline into which all or part of a stream disappears underground ( Jackson, 1997).
swamp An area saturated with water throughout much of the year but with the surface of the soil usually not deeply submerged. Usually dominated by tree or shrub vegetation. Compare marsh, bog, fen, and miscellaneous areas.
swash zone The sloping part of the beach that is alternately covered and uncovered by the uprush of waves, and where longshore movement of water occurs in a zigzag (upslope-downslope) manner ( Jackson, 1997). Compare shoreline.
sweep Refer to tillage, sweep.
swell (not recommended) Refer to swell and swale topography.
swell and swale topography A local scale topography composed of small, well-rounded hillocks and shallow, closed depressions irregularly spaced across low-relief ground moraine (slopes generally 2 – 6%); the effect is a subdued, irregularly undulating surface that is common on ground moraines. Micro-elevational differences generally range from < 1 to < 5 m (Schoeneberger and Wysocki, personal communication, 2013).
swelling The process that occurs when interacting clay platelets move apart.
symbiosis The obligatory cohabitation of two dissimilar organisms in intimate association, usually but not always, to their mutual benefit.
symmetry concentration
(no longer used in SSSA publications) That quantity of cations (or anions) equivalent to the exchange capacity of a soil. For example, if the cation exchange capacity of a soil is 10 cmolc kg-1 of soil, then 1 symmetry concentration is 10 cmol of any monovalent cation or 5 cmol of any divalent cation.
symmetry value (no longer used in SSSA publications) The quantity of adsorbed ion released when one symmetry concentration of another ion is added.
syncline [landform] A unit of folded strata that is concave upward whose core contains the stratigraphically younger rocks, and occurs at the earth’s surface. In a single syncline, beds forming the opposing limbs of the fold dip toward its axial plane (Schoeneberger and Wysocki, personal communication, 2013; Hawley and Parson, 1980). Compare monocline, syncline, fold.
synergism (i) The nonobligatory association between organisms that is mutually beneficial. Both populations can survive in their natural environment on their own although, when formed, the association offers mutual advantages. (ii) The simultaneous actions of two or more factors that have a greater total effect together than the sum of their individual effects.