Gabbro A coarse-grained, basic igneous rock similar in mineral composition to basalt.
gap A sharp break or opening in a mountain ridge, or a short pass through a mountain range; for example, a wind gap ( Jackson, 1997).
gas diffusivity Coefficient describing the process of gas interchange between the soil and the atmosphere, often described as the ratio of the diffusion coefficient to the diffusion coefficient in free space.
gas pressure (external) potential Refer to air pressure in Table 1.
Gelands [soil taxonomy] A suborder of Andisols that typically have a mean annual temperature equal to or less than 0°C and a mean summer soil temperature<8°C (without an O horizon) or <0°C (with an O horizon). Gelands may have mollic, umbric , or other diagnostic horizons (USDA, 2006; Appendix 1).
Gelepts [soil taxonomy] A suborder of Inceptisols that typically have a mean annual temperature equal to or <0°C and a mean summer soil temperature <8°C (without an O horizon) or <0°C (with an O horizon). Gelepts have free carbonates in the profile and/or base saturation equal to or >60% between 25 and 75 cm depths (or directly above a root limiting layer (USDA, 2006; Appendix 1).
gelifraction (not recommended) Use frost shattering.
gelivation (not recommended) Use frost shattering.
Gellisols [soil taxonomy] An order of organic and mineral soils that have gelic materials (e.g., sand wedges and ice crystals) underlain by permafrost. Diagnostic horizons, including ochric, mollic, umbric, and histic epipedons and argillic, salic, gypsic, and calcic horizons, may or may not be present. Cryoturbation (frost mixing) is an important process in many Gelisols and results in irregular or broken horizons, involutions, organic matter accumulation on the permafrost table, oriented rock fragments, and silt caps on rock fragments. (USDA, 1999; Appendix 1).
Gelolls [soil taxonomy] A suborder of Mollisols that have a gelic soil temperature regime (USDA, 2004; refer to Appendix 1).
genetic Resulting from, or produced by, soil-forming processes; for example, a genetic soil profile or a genetic horizon.
geographic information system (GIS) A method of overlaying large volumes of spatial data of different kinds. The data are referenced to a set of geographical coordinates and encoded in a form suitable for handling by a digital computer. Different data planes can be overlain, statistically analyzed, and used to make estimates of soil and land suitabilities.
geological erosion
Refer to erosion, geological erosion.
geometric mean diameter Index of aggregate size based on the exponential of natural log mean:
geometric standard deviation The standard deviation related to the geometric mean diameter.
geomorphic component mountains A set of fundamental, three dimensional areas and positions of mountains. In descending, topographic order, the geomorphic components of a simple mountain are the mountaintop (roughly analogous to the crest or summit); mountainflank (the long slope along the sides of mountains which can be further subdivided into three portions based on the relative slope location: upper third-, middle third-, or lower third mountainflank); free face (rock outcrop); and the mountainbase (colluvium/slope alluvium apron at the bottom of the mountain; Schoeneberger and Wysocki, personal communication, 2013).
geomorphic component
A fundamental, three dimensional area and position of a geomorphic setting (i.e., hills, mountains, terraces, flat plains) that has unique and prevailing kinetic energy dynamics and sediment transport conditions whch result in their characteristic form, patters of sedimentation and soil development (Schoeneberger and Wysocki, personal communication, 2013).
geomorphic component flat plains A set of fundamental, three dimensional areas and positions of flat plains. In descending topographic order, the geomorphic components of a simple, flat plain (e.g., lake plain, low coastal plain, etc.) are the rise [a broad, slightly elevated area with comparatively greater gradients (e.g., 1-3% slopes], and the talf [a comparatively level (e.g., 0-1% slopes), laterally extensive, non-fluvial area], and dip (a slight depression that is not a permanent water body nor part of an integrated drainage network). Compare geomorphic component terraces (Schoeneberger and Wysocki, personal communication, 2013).
geomorphic component hills A set of fundamental, three dimensional areas and positions that geomorphically define a hill or ridge. In descending topographic order, the geomorphic components of a simple hill are the interfluve (stable summit area); crest (unstable summit, converged shoulders); three geomorphic slope areas defined by plan shape and its influence on overland flow and throughflow: head slope (convergent flow), side slope (parallel flow), nose slope (divergent flow) and free face (rock outcrop); and the base slope (concave accretion area: colluvium/slope alluvium apron at hill bottom; Schoeneberger and Wysocki, personal communication, 2013). where Yis the geometric mean diameter, wi is weight of aggregates in a size class of average diameter xi (Mazurak, 1950).
geomorphic component – terraces, stepped landforms A set of fundamental, three dimensional areas and positions of terraces, flood-plain steps, and other stepped landforms (e.g., stacked lava flow units). In descending topographic order, the geomorphic components are the tread (the level to gently sloping, laterally extensive top of a terrace, flood-plain step, or other stepped landform); and the riser (the comparatively short escarpment forming the more steeply sloping edge that descends to another level or a channel; Schoeneberger and Wysocki, personal communication, 2013).
geomorphic surface A mappable area of the earth’s surface that has a common history; the area is of similar age and is formed by a set of processes during an episode of landscape evolution. A geomorphic surface can be erosional, constructional, or both. The surface shape can be planar, concave, convex, or any combination of these. Compare constructional, erosional (Ruhe, 1975).
geomorphology The science that studies the evolution of the earth’s surface. The science of landforms. The systematic examination of landforms and their interpretation as records of geologic history (Ruhe, 1975). Compare soil geomorphology.
geyser A type of hot spring that intermittently erupts jets of hot water and steam, the result of ground water coming in contact with rock or steam hot enough to create steam under conditions preventing free circulation; a type of intermittent spring ( Jackson, 1997). Compare mud pot, hot spring.
geyser basin A valley that contains numerous springs, geysers, and steam fissures fed by the same ground-water flow ( Jackson, 1997).
geyser cone A low hill or mound built up of siliceous sinter around the orifice of a geyser ( Jackson, 1997). unique and prevailing kinetic energy dynamics andsediment transport conditions which result in their characteristic form, patterns of sedimentation and soil development (Schoeneberger and Wysocki, personal communication, 2013).
giant ripple A ripple that is more than 30 m in length; e.g., the jokulhlaup derived giant ripples in Camas Prairie, MT; it usually exhibits superimposed megaripples. Compare ripple mark ( Jackson, 1997).
Gibbs free energy (G) The thermodynamic potential for a system whose independent variables are the absolute temperature, applied pressure, mass variables, and other independent, extensive variables. The change in Gibbs free energy, as a system passes reversibly from one state to another at constant temperature and pressure, is a measure of the work available in that change of state.
gibbsite
Al(OH)3, a mineral with a platy habit that occurs in highly weathered soils and in laterite. Also, may be prominent in the subsoil and saprolite of soils formed on crystalline rock high in feldspar.
gilgai The microrelief of microbasins and microknolls on level areas or of microtroughs and microridges parallel to the slope on sloping areas of the soil surface produced by expansion and contraction and shear/ thrust processes during wetting and drying of clayey soils that contain smectite; (usually in regions with distinct, seasonal, precipitation patterns). Various types of gilgai can be recognized based on the dominant shape of micro-highs and micro-lows: circular gilgai, elliptical gilgai, and linear gilgai. Also referred to, in part or in total, as crabhole, Bay of Biscay, or hushabye in older literature (Schoeneberger and Wysocki, personal communication, 2013). Compare microrelief.
glacial (adjective) (a) Of or relating to the presence and activities of ice and glaciers, as in glacial erosion.(b) Pertaining to distinctive features and materials produced by or derived from glaciers and ice sheets, as in glacial lakes. (c) Pertaining to an ice age or region of glaciation ( Jackson, 1997).
glacial drainage channel A channel formed by an ice-marginal, englacial, or subglacial stream during glaciation ( Jackson, 1997).
glacial drift (not recommended, use drift). A general, redundant term applied to all mineral material transported by a glacier and deposited directly by or from the ice, or by running water emanating from a glacier. Drift includes unstratified material (till) that forms moraines, and stratified glaciofluvial deposits that form outwash plains, eskers, kames, varves, and glaciolacustrine sediments.
glacial groove A deep, wide, usually straight furrow cut in bedrock by the abrasive action of a rock fragment embedded in the bottom of a moving glacier; it is larger and deeper than a glacial striation, ranging in size from a deep scratch to a small glacial valley ( Jackson, 1997). Compare flute.
glacial lake (a) A lake that derives much or all of its water from the melting of glacier ice, fed by meltwater, and lying outside the glacier margins (e.g., proglacial lake) or lying on a glacier (e.g., ice-walled lake, icefloored lake) and due to differential melting. (b) A lake occupying a basin produced by glacial deposition, such as one held in by a morainal dam. (c) A lake occupying a basin produced in bedrock by glacial erosion (scouring, quarrying); e.g., cirque lake, fjord. (iv) A lake occupying a basin produced by collapse of outwash material surrounding masses of stagnant ice ( Jackson, 1997).
glacial outwash (not recommended) Use outwash.
glacial soil A soil derived from glacial drift. (Not used in current U.S. system of soil taxonomy.)
glacial till (not recommended) Refer to till (i). Till should only be used for describing glacial sediments, therefore “glacial till” is redundant (Goldthwaite and Matsch, 1988).
glacial-marine sedimentation The accumulation of glacially eroded, terrestrially derived sediment in the marine environment. Sediment may be introduced by fluvial transport, by ice rafting, as an ice-contact deposit, or by eolian transport. Compare glaciomarine deposits ( Jackson, 1997).
glacial-valley floor The comparatively flat bottom of a mountain valley predominantly mantled by till but which can grade from glacial scour (scoured rock-outcrop) near it’s head to a thick mantle of till, and ultimately merging with alluvium or colluvium further down valley. Some glacial-valley floors descend downstream in a series of scour-derived steps which may contain sequential tarn lakes (pater noster lakes); (not preferred: colloquial–western USA) sometimes called a trough bottom (Schoeneberger and Wysocki, personal communication, 2013).
glacial-valley wall The comparatively steep, glacially scoured, concave sides of a u-shaped, mountain valley mantled by colluvium with little or no till; (not preferred: colloquial–western USA) sometimes called a trough wall (Schoeneberger and Wysocki, personal communication, 2013).
glaciation The formation, movement and recession of glaciers or ice sheets. A collective term for the geologic processes of glacial activity, including erosion and deposition, and the resulting effects of such action on the earth’s surface ( Jackson, 1997).
glacier A large mass of ice that formed, in part, on land by the compaction and recrystallization of snow and surviving from year to year. The ice-mass is, or has at one time, moved downslope or outward in all directions because of the stress of its own weight, or it may be stagnant or retreating. Compare alpine glacier, snowfield, rock glacier ( Jackson, 1997).
glacier outburst flood A sudden, often annual, release of meltwater from a glacier or glacier-damned lake sometimes resulting in a catastrophic flood, formed by melting of a drainage channel or buoyant lifting of ice by water or by subglacial volcanic activity; also called jokulaup. Synonym jokulhlaup. Compare scabland, giant ripple ( Jackson, 1997).
glaciofluvial deposits Material moved by glaciers and subsequently sorted and deposited by streams flowing from the melting ice. The deposits are stratified and may occur in the form of outwash plains, deltas, kames, eskers, and kame terraces. Compare glacial drift and till (i).
glaciokarst
Karst in glaciated terrain developed on bedrock susceptible to dissolution (e.g., limestone), relatively thinly mantled (e.g., <50 m) with glacial drift and characterized by surficial, closed depressions formed by post-glacial, subsurface karstic collapse (e.g., sinkholes) rather than by glacial processes (e.g., ice-block meltout); common in Indiana, Michigan (Schoeneberger and Wysocki, personal communication, 2013; Jackson, 1997). Compare karst.
glaciolacustrine deposits Material ranging from fine clay to sand derived from glaciers and deposited in glacial lakes by water originating mainly from the melting of glacial ice. Many are bedded or laminated with varves or rhythmites (Hawley and Parsons, 1980).
glaciomarine deposit Glacially eroded, terrestrially derived sediments (clay, silt, sand, and gravel) that accumulated on the ocean floor. Sediments may be accumulated as an ice-contact deposit, by fluvial transport, ice-rafting, or eolian transport (Goldthwaite and Matsch, 1988; Jackson, 1997).
glade (colloquial – Ozark uplands, USA) (a) A largely treeless, open, grassy area (e.g., oak savanna) on high, broad interfluves and hillsides, commonly with shallow soils (Schoeneberger and Wysocki, personal communication, 2013). Compare park. (b) (not preferred) refer to park: An ecological term for a grassy, open depression or small valley as in a high meadow; sometimes marshy and forming the headwaters of a stream, or a low, grassy marsh that is periodically inundated (Jackson, 1997; Schoeneberger and Wysocki, personal communication, 2013).
glaebule A three-dimensional unit within the s-matrix of the soil material. Its morphology is incompatible with its present occurrence being within a single void in the present soil material. It is recognized as a unit either because of a greater concentration of some constituent and/or a difference in fabric compared with the enclosing soil material, or because it has a distinct boundary with the enclosing soil material.
glauconite
An Fe-rich dioctahedral mica with tetrahedral Al (or Fe3+) usually greater than 0.2 atoms per formula unit and octahedral R3+correspondingly greater than 1.2 atoms. A generalized formula is K(R1.333+R 2+) (Si3.67Al0.33)O10(OH)2 with Fe3+ >>Al and Mg>Fe(II)(unless altered). Further characteristics are d(060)>0.151 nm and (usually) broader infrared spectra than celadonite. Mixtures containing an iron-rich mica as a major component can be called glauconitic.
glauconite pellets Silt to sand-sized, nodular aggregates with a characteristic greenish color, dominantly composed of the clay mineral glauconite; formed in near-shore marine sediments and subsequently exposed by a drop in sea level or rise of a land mass, as on a coastal plain. Glauconite pellets have a high potassium content and higher CEC and moisture retention compared to other mineral sands. Compare greensands (Schoeneberger and Wysocki, personal communication, 2013).
Gley soil A generic name for soil oils developed under conditions of poor drainage resulting in reduction of iron and other elements and in gray colors and mottles. (Not used in soil taxonomy).
gleyed A soil condition resulting from prolonged soil saturation, which is manifested by the presence of bluish or greenish colors through the soil mass or in mottles (spots or streaks) among the colors. Gleying occurs under reducing conditions, by which iron is reduced predominantly to the ferrous state.
gleyzation A soil-forming process resulting in the development of gley soils. (Not used in current U.S. system of soil taxonomy.)
Glomalin A sugar-protein complex secreted by certain fungi primarily in plant rhizosphere that is thought to contribute to soil aggregation.
glossic horizon [soil taxonomy] A diagnostic, subsurface mineral layer containing vertical tongues of albic material formed by the stripping of clay and iron oxides from the surface of soil peds and progressing towards the ped interior in an argillic, kandic, or natric horizon. Between 15 and 85% of the volume of the original horizon has been consumed by this process. A glossic horizon generally occurs between an overlying albic horizon and an underlying argillic, kandic, or natric horizon or fragipan (USDA, 1999).
goethite FeOOH. A yellow-brown iron oxide mineral. Goethite occurs in almost every soil type and climatic region and is responsible for the yellowish-brown color in many soils and weathered materials.
gorge (a) A narrow, deep valley with nearly vertical, rocky walls, smaller than a canyon, and more steep-sided than a ravine; especially a restricted, steep-walled part of a canyon. (b) A narrow defile or passage between hills or mountains ( Jackson, 1997).
graben An elongate trough or basin bounded on both sides by high-angle, normal faults that dip towards the interior of the trough. It is a structural form that may or may not be geomorphically expressed as a rift valley. Compare horst, half-graben ( Jackson, 1997).
gradient The rate of change of a potential with distance parallel to flow.
Grady pond Refer to Carolina Bay.
grain cutan Cutan associated with the surfaces of skeleton grains or other discrete units such as nodules, concretions, etc.
grain density Refer to particle density.
granite A coarse-grained, acid igneous rock containing chiefly alkali feldspar and quartz and some mica and/or hornblende.
granitoid (a) In the International Union of Geological Sciences (IUGS) classification, a preliminary term (for field use) for a plutonic rock with Q (quartz) between 20 and 60(%). (b) A general term for all phaneritic igneous rocks (mineral crystals visible unaided and all about the same size) dominated by quartz and feldspars (Schoeneberger and Wysocki, personal communication, 2013; Jackson, 1997).
granular soil structure A type of soil structure. Compare soil structure and soil structure types.
granulation The process of producing granular materials (e.g., granular soil structure).
granule A natural soil aggregate or ped of relatively low porosity. Compare soil structure and soil structure shapes.
grassed waterway Refer to erosion, grassed waterway.
grassy organic materials Use organic materials.
gravel Rounded or partially rounded rock or mineral fragments between 2 and 75 mm in diameter. Size may be further refined as fine gravel (2-5 mm diameter), medium gravel (5-20 mm diameter), and coarse gravel (20-75 mm diameter). Compare rock fragments.
gravel pit A depression, ditch or pit excavated to furnish gravel for roads or other construction purposes; a type of borrow pit (Schoeneberger and Wysocki, personal communication, 2013).
gravelly (adjective) (a) Containing ≥15% but<35% gravel-sized (>2 and <76 mm) rock fragments (USDA). (b) (not preferred) A generic, informal modifier meaning “containing appreciable amounts of gravel”. Compare rock fragments.
gravimetric water content Ratio of the mass of water in a soil to the mass of oven dry (105°C) soil.
gravitational potential Refer to gravity head.
gravitational water Water that moves into, through, or out of the soil under the influence of gravity. Compare soil water, soil water potential.
gravitropism The natural tendency for biological organisms or specific cells or organs of an organism to respond to the stimulus of gravity.
gravity flow Water flow due to the force of gravity. Used in irrigation, drainage, inlets, and outlets.
gravity head (gravity potential) The amount of work required to raise a body a specified height in a gravity field. Gravity head is expressed as energy per weight and is equal to the distance Z, of a measurement point in the soil above an arbitrary reference height (z). Gravity potential is expressed as energy per volume and is equal to the product of the distance raised, Z, the water density, r and the gravitation constant, g (ρgZ).
gravity irrigation Refer to irrigation, gravity sprinkler.
Gray Desert soil [Russian soil classification] A term synonymous with Desert soil. (Not used in soil taxonomy.)
Gray-Brown Podzolic soil [soil classification] (obsolete; not used in soil taxonomy) A zonal great soil group consisting of soils with a thin, moderately dark A1 (A) horizon and with a grayish-brown A2 (E) horizon underlain by a B horizon containing a high percentage of bases and an appreciable quantity of illuviated silicate clay; formed on relatively young land surfaces, mostly glacial deposits, from material relatively rich in calcium, under deciduous forests in humid temperate regions (Baldwin, et al., 1938).
great soil group [soil classification] One of the categories in the system of soil classification in the United States for many years. Great groups place soils according to soil moisture and temperature, base saturation status, and expression of horizons. Compare classification, soil.
green manure Plant material incorporated into soil while green or at maturity, for soil improvement.
green manure crop Any crop grown for the purpose of being turned under while green or soon after maturity for soil improvement.
Greenhouse effect The absorption of solar radiant energy by the earth’s surface and its release as heat into the atmosphere; longer infrared heat waves are absorbed by the air, principally by carbon dioxide and water vapor; Thus the atmosphere traps heat much as does the glass in a greenhouse.
greensands (a) An unconsolidated, near-shore marine sediment containing substantial amounts of dark greenish glauconite pellets, often mingled with clay or sand (quartz may form the dominant constituent); prominent in Cretaceous and Tertiary coastal plain strata of New Jersey, Delaware and Maryland; has been commercially mined for potassium fertilizer. The term is loosely applied to any glauconitic sediment. (b) (not preferred – use glauconitic sandstone) A sandstone consisting of greensand that is commonly poorly cemented, and has a greenish color when unweathered but an orange or yellow color when weathered. Compare glauconite pellets (Schoeneberger and Wysocki, personal communication, 2013).
grike (not preferred) Use cutter.
groove A small, natural, narrow drainageway on high angle slopes which separate tertiary spur ridges or mini-interfluves and is a constituent part of rib and groove topography; common in well dissected uplands (Schoeneberger and Wysocki, personal communication, 2013). Compare rib.
gross primary productivity (GPP) Total carbon assimilation by plants. GPP = NPP + respiration losses. Compare net primary productivity.
gross duty of water Refer to irrigation, gross duty of water.
ground soil Any soil at the present-day land surface and actively undergoing pedogenesis, regardless of its history (i.e., relict, exhumed; Schoeneberger and Wysocki, personal communication, 2013; Ruhe, 1975). Compare buried soil.
ground data Supporting data collected on the ground, and information derived there from, as an aid to the interpretation of remotely recorded surveys, such as airborne imagery, etc. Generally, this should be performed concurrently with the airborne surveys. Data as to weather, soils, and vegetation types and conditions are typical.
ground moraine (a) [landform] Commonly an extensive layer low-relief area of till, having an uneven or undulating surface bounded on the distal end by a recessional or end moraine. (b) [Parent Material]; a deposit of rock and mineral debris dragged along, in, on, or beneath a glacier and emplaced by processes including basal lodgement and release from downwasting stagnant ice by ablation (Schoeneberger and Wysocki, personal communication, 2013). Compare end moraine, recessional, moraine, terminal moraine.
Ground-Water Laterite soil [soil classification] (obsolete; not used in soil taxonomy) A great soil group of the intrazonal order and hydromorphic suborder, consisting of soils characterized by hardpans or concretional horizons rich in iron and aluminum (and sometimes manganese) that have formed immediately above the water table (Baldwin, et al., 1938).
Ground-Water Podzol soil [soil classification] (obsolete; not used in soil taxonomy) A great soil group of the intrazonal order and hydromorphic suborder, consisting of soils with an organic mat on the surface over a very thin layer of acid humus material underlain by a whitish-gray leached layer, which may be as much as 61 or 91 cm (2 or 3 feet) in thickness, and is underlain by a brown, or very dark-brown, cemented hardpan layer; formed under various types of forest vegetation in cool to tropical, humid climates under conditions of poor drainage (Baldwin, et al., 1938).
groundwater That portion of the water below the surface of the ground at a pressure equal to or greater than atmospheric. Compare water table.
grus The fragmental products of in situ granular disintegration of granite and granitic rocks, dominated by inter-crystal disintegration. Compare saprolite (Schoeneberger and Wysocki, personal communication, 2013; Jackson, 1997).
guano The decomposed dried excrement of birds and bats, commonly high in nitrogen, used for fertilizer.
guess row Refer to tillage, guess row.
gulch (colloquial: western USA; not preferred use ravine) A small stream channel, narrow and steep-sided in cross section, and larger than a gully, cut in unconsolidated materials. General synonym ravine. Compare arroyo, draw, gully, wash (Hawley and Parsons, 1980).
gulf A relatively large part of an ocean or sea extending far into the land, partly enclosed by an extensive sweep of the coast, and opened to the sea through a strait (e.g., Gulf of Mexico); the largest of various forms of inlets of the sea. It is usually larger, more enclosed, and more deeply indented than a bay (Jackson, 1997). Compare bay.
gullied land [soil survey] A miscellaneous area (map unit) applied where all diagnostic soil horizons have been removed by water, resulting in a network of V-shaped or U-shaped channels. Some areas resemble miniature badlands. Generally, gullies are so deep that extensive reshaping is necessary for most uses (USDA, 1993).
gully Refer to erosion, gully.
gut [channel] A tidal stream connecting two larger waterways within a lagoon, estuary or bay; also called a tidal channel (Schoeneberger and Wysocki, personal communication, 2013; Jackson, 1997).
gypsan A cutan composed of gypsum.
gypsic horizon [soil taxonomy] A diagnostic, subsurface mineral soil horizon of secondary CaSO4 enrichment that (i) is >15 cm thick, (ii) isn’t a petrogypsic horizon, (iii) is 5% or more gypsum and 1% or more (by volume) secondary visible gypsum; and (iv) the product of the thickness in centimeters and the amount of CaSO4 is equal to or <150 g kg–1.
Gypsids [soil taxonomy] A suborder of Aridisols which have a gypsic or petrogypsic horizon whose upper boundary is within 100 cm of the soil surface and lack a petrocalcic horizon overlying any of these horizons. Gypsids have an aridic soil moisture regime (USDA, 1999; Appendix I).
gypsite
An earthy gypsum (CaSO4∙2H2O) variety that contains various quantities (i.e., < 50%) of soil material, silicate clay minerals and sometimes other salts (e.g., NaCl); found only in arid or semi-arid regions as secondary precipitation concentrations or efflorescence associated with rock gypsum or gypsum-bearing strata. Compare rock gypsum, rock anhydrite (Schoeneberger and Wysocki, personal communication, 2013; Jackson, 1997).
gypsum
CaSO4 • 2H2O. The common name for calcium sulfate, used to supply calcium to ameliorate soils with a high exchangeable sodium fraction.
gypsum land [soil survey] A miscellaneous area (map unit) applied to areas of nearly pure, soft gypsum. The surface is generally very unstable and erodesd easily; trafficability is very poor. Note: areas of hard gypsum are mapped as rock-outcrop (USDA, 1993).
gypsum requirement The quantity of gypsum or its equivalent required to reduce the exchangeable sodium fraction of a given amount of soil to an acceptable level where dispersion of soil colloids does not take place.
gyttja Sedimentary peat consisting mainly of plant and animal residues precipitated from standing water.