Glossary of Soil Science Terms - Browse
maar
A low relief, broad volcanic crater formed by multiple, shallow explosive eruptions. It is surrounded by a crater ring in the form of low ramparts of gently dipping (i.e., <25 degrees), well-bedded ejecta; may be partially or completely filled by water (maar lake; Jackson, 1997; Schoeneberger and Wysocki, personal communication, 2013).
macronutrient
A plant nutrient found at relatively high concentrations (>500 mg kg-1) in plants. Usually refers to N, P, and K but may include Ca, Mg, and S.
macropore Large pores responsible for preferential flow and rapid, far-reaching transport. Refer to Table 3.
macropore flow The tendency for water applied to the soil surface at rates exceeding the upper limit of unsaturated hydraulic conductivity, to move into the soil profile mainly via saturated flow through macropores, thereby bypassing micropores and rapidly transporting any solutes to the lower soil profile. Compare preferential flow.
made land Areas filled with earth, or with earth and trash mixed, usually by or under the control of humankind. Compare miscellaneous areas.
mafic rock A general term for igneous rock composed chiefly of one or more ferromagnesian, dark-colored minerals; also said of those minerals ( Jackson, 1997). Compare felsic rock.
maghemite
Fe2O3 A dark reddish-brown, magnetic iron oxide mineral chemically similar to hematite, but structurally similar to magnetite. Often found in welldrained, highly weathered soils of tropical regions.
magnetite
Fe3O4 A black, magnetic iron oxide mineral usually inherited from igneous rocks. Often found in soils as black magnetic sand grains.
main scarp The steep surface on undisturbed ground at the upper edge of a landslide, caused by movement of displaced material away from the undisturbed ground; it is visible a part of the surface of rupture (slip surface; Cruden and Varnes, 1996). Compare minor scarp, toe.
mainland cove A subaqueous area adjacent to the mainland or a submerged mainland beach that forms a minor recess or embayment within the larger basin (Subaquesous Soils Subcommittee, 2005). Compare cove, barrier cove. Table 3. Pore-size classification. (after Brewer, R. 1964. Fabric mineral analysis of soils, John Wiley & Sons).
maintenance application Application of fertilizer materials in amounts and at intervals to maintain available soil nutrients at levels necessary to produce a desired yield.
mangan A cutan composed of manganese oxide or hydroxide.
manganese oxides A group term for oxides of manganese. They are typically black and frequently occur in soils as nodules and coatings on ped faces usually in association with iron oxides. Birnessite and lithiophorite are common manganese oxide minerals in soils.
mangrove swamp A tropical or subtropical marine swamp formed in a silty, organic, or occasionally a coralline substratum and characterized by abundant mangrove trees along the seashore in a low area of salty or brackish water affected by daily tidal fluctuation but protected from violent wave action by reefs or land; dominated by saturated soils, commonly sulfaquents ( Jackson, 1997; Schoeneberger and Wysocki, personal communication, 2013).
manifold Refer to irrigation, manifold.
manure The excreta of animals, with or without an admixture of bedding or litter, fresh or at various stages of further decomposition or composting. In some countries, may denote any fertilizer material.
map unit, soil (a) A conceptual group of one to many delineations identified by the same name in a soil survey that represent similar landscape areas comprised of either: (i) the same kind of component soil, plus inclusions, or (ii) two or more kinds of component soils, plus inclusions, or (iii) component soils and miscellaneous area, plus inclusions, or (iv) two or more kinds of component soils that may or may not occur together in various delineations but all have similar special use and management, plus inclusions, or (v) a miscellaneous area and included soils. (b) A loose synonym for a delineation. Compare component soil, delineation, inclusion, miscellaneous areas, soil association, soil complex, soil consociation, undifferentiated group.
map, medium-scale A map having a scale from 1:100,000, exclusive, to 1:1,000,000, inclusive.
map, large-scale A map having a scale of 1:100,000 or larger.
map, small-scale A map having a scale smaller than 1:1,000,000.
marine deposit Sediments (predominantly sands, silts and clays) of marine origin; laid down in the salty waters of an ocean. Compare estuarine deposit, lagoonal deposit (Schoeneberger and Wysocki, personal communication, 2013).
marine lake [water] An inland body of permanently standing brackish or saline water, occupying a depression on the Earth’s surface whose water level is commonly influenced by ocean tides through subterranean cavities connecting to nearby lagoons; generally of appreciable size (larger than a pond) and too deep to permit emergent vegetation to take root completely across the expanse of water. Such water bodies can have unique biotia (e.g., stingless jellyfish of Palau; Schoeneberger and Wysocki, personal communication, 2013).
marine terrace A constructional coastal strip, sloping gently seaward, veneered by marine deposits (typically silt, sand, fine gravel; Jackson, 1997). Compare terrace, wave-built terrace, karstic marine terrace.
marl An earthy, soft and unconsolidated calcium carbonate, usually mixed with varying amounts of clay or other impurities in approximately equal proportions (35 to 65% of each); formed primarily under freshwater lacustrine conditions (freshwater marl), but varieties associated with more saline environments (coastal marl) also occur (Hawley and Parsons, 1980).
marsh A wet area, periodically inundated with standing or slow moving water, that has grassy or herbaceous vegetation and often little peat accumulation; the water may be salt, brackish, or fresh. Sometimes called wet prairies. Compare swamp, tidal flats, and wetland.
mass The property of a material that describes the quantity of matter in it; the ratio of the weight of a body and the acceleration due to gravity.
mass wasting (slumping) The downslope movement of soil, rock, and regolith, under the influence of gravity. Slow mass wasting processes are also termed soil creep and solifluction and rapid mass wasting is also termed slumping, slides, and debrisor mud-floes. Synonym mass movement. Refer to bank failure.
mass balance Used as an indicator of the accuracy of numerical computations. The mass balance is the absolute error in the water volume computation, that is, sum of the net flux through the domain and the net volumetric change within the domain. It is often expressed as a percentage by dividing the water volume of the flow domain.
mass flow (nutrient) The movement of solutes associated with net movement of water.
mass movement A generic term for any process or sediments (mass movement deposit) resulting from the dislodgement and downslope transport of soil and rock material as a unit under direct gravitational stress. The process includes slow displacements such as creep and solifluction, and rapid movements such as landslides, rock slides, and falls, earthflows, debris flows, and avalanches. Agents of fluid transport (water, ice, air) may play an important, if subordinate, role in the process (Hawley and Parsons, 1980). Synonym mass wasting.
mass slumping (obsolete) Use mass wasting.
mass transfer Movement of mass, typically used to refer to solutes, between flow regions.
mass-movement till (not preferred) Use flow till
matric potential (matric head) Potential energy of soil water due to the attractive forces (adhesion and cohesion) between water and the soil matrix. Matric potential is expressed as energy per unit volume and equals the product of the height of rise in a capillary tube, hm, the water density, ρ, and the gravitational constant, g (ρghm). Matric head is expressed as energy per weight and is equal to the height of rise in a capillary tube (hm).
matric suction (no longer used in SSSA publications.) The preferred term is matric potential. Compare soil water, soil water potential.
mature soil A soil with well-developed soil horizons produced by the natural processes of soil formation and essentially in equilibrium with its present environment.
mawae (colloquial: Hawaii) A natural surface channel commonly found near the middle of an a’a lava flow, formed by the surficial draining of molten lava rather than by erosion from running water; a type of lava trench (MacDonald and Abbott, 1970). Compare lava tube.
maximum contaminant level (MCL) The highest chemical concentration permissible in a water source as defined by the regulatory authority.
meander [streams] One of a series of regular freely developing sinuous curves, bends, loops, turns, or windings in the course of a stream ( Jackson, 1997).
meander land [soil survey] (obsolete) A former miscellaneous area (map unit) applied to areas of unsurveyed land along a lake shore or stream border that has developed by the receding of the shore line or of the stream since the last cadastral survey of the area.
meander scroll (a) One of a series of long, parallel, close fitting, crescent-shaped ridges and troughs formed along the inner bank of a stream meander as the channel migrated laterally down-valley and toward the outer bank. Compare meander belt, point bar. (b) (not recommended; use oxbow lake) A small, elongate lake on a flood plain in a well-defined part of an abandoned stream channel ( Jackson, 1997).
meander belt The zone within which migration of a meandering channel occurs; the flood-plain area included between two imaginary lines drawn tangential to the outer bends of active channel loops. Landform components of the meander-belt surface are produced by a combination of gradual (lateral and down-valley) migration of meander loops and avulsive channel shifts causing abrupt cut-offs of loop segments. Landforms flanking the sinuous stream channel include: point bars, abandoned meanders, meander scrolls, oxbow lakes, natural levees, and flood-plain splays. Meander belts may not exhibit prominent natural levee or splay forms. Flood plains of broad valleys may contain one or more abandoned meander belts in addition to the zone flanking the active stream channel (Hawley and Parsons, 1980).
meander scar (a) A crescent-shaped, concave or linear mark on the face of a bluff or valley wall, produced by the lateral erosion of a meandering stream which impinged upon and undercut the bluff; if it’s no longer adjacent to the modern stream channel it indicates an abandoned route of the stream (Schoeneberger and Wysocki, personal communication, 2013); (b) (not recommended, use oxbow) An abandoned meander, commonly filled in by deposition and vegetation, but still discernable ( Jackson, 1997).
meandering channel The term “meandering” should be restricted to loops with channel length more than 1.5 to 2 times the meander wave length. Meandering stream channels commonly have cross sections with low width-to-depth ratios, cohesive (fine-grained) bank materials, and low gradient. At a given bank-full discharge, meandering streams have gentler slopes, and deeper narrower, and more stable channel cross sections than braided streams (Hawley and Parson, 1980; Ruhe, 1975). Compare meander, braided stream, flood-plain landforms.
mechanical analysis (not preferred) An informal name for particle-size analysis. Compare particle size distribution.
mechanical impedance Traffic or load resulting in dense soil with high strength.
mechanical weathering The process of weathering by which frost action, salt-crystal growth, absorption of water, and other physical processes break down a rock into smaller fragments; no chemical change is involved. Synonym physical weathering. Compare chemical weathering.
medial moraine (a) An elongate moraine carried in or upon the middle of a glacier and parallel to its sides, usually formed by the merging of adjacent and inner lateral moraines below the junction of two coalescing valley glaciers. (b) A moraine formed by glacial abrasion of a rocky protuberance near the middle of a glacier and whose debris appears at the glacier surface in the ablation area. (c) The irregular ridge left behind in the middle of a glacial valley, when the glacier on which it was formed has disappeared ( Jackson, 1997).
medium-textured Texture group consisting of very fine sandy loam, loam, silt loam, and silt textures. Compare soil texture.
melt-out till A till that may be either subglacial or supraglacial in origin that forms by slow melting of debris-rich stagnant ice, but without secondary flow processes. Thus, the fabric and clast orientations imparted by ice processes remain mostly intact (Schoeneberger and Wysocki, personal communication, 2013; Jackson, 1997). Compare subglacial till, supraglacial till, flow till, lodgment till.
mesa An isolated, flat-topped landform that stands distinctly above the adjacent land area and is bounded by steep slopes or cliffs and is generally capped by erosion resistant, nearly horizontal rock (often lava). Mesas and buttes have similar forms and isolated occurrence. A mesa has a summit area broader than the bounding cliff height. Mesas are most common in arid and semi-arid regions, but are not climatically restricted (Schoeneberger and Wysocki, personal communication, 2013; Jackson, 1997). Compare butte, plateau, cuesta.
mesic [soil taxonomy] A soil temperature regime that has mean annual soil temperatures of 8°C or more but<15°C, and >5°C difference between mean summer and mean winter soil temperatures at 50 cm below the surface. Isomesic is the same except the summer and winter temperatures differ by <5°C.
mesobiota Refer to mesofauna.
mesofauna Nematodes, oligochaete worms, smaller insect larvae, and microarthropods.
mesophile Refer to mesophilic organism.
mesophilic organism An organism whose optimum temperature for growth falls in an intermediate range of approximately 15 to 35°C. Synonym “mesophile.”
mesopore A secondary pore class between macropores and micropores that contributes to water flow and solute movement by advection and diffusion. Refer to pore-size classification.
meta-stable slope (not recommended; obsolete) A slope that is relatively stable at the present time, but may become active if the environmental balance is disturbed, for instance, by road construction or destruction of vegetation. A metastable slope is often related to base levels of former geomorphic episodes. The regolith is generally moderately deep, may contain stone lines or relict evidence of slope alluvium. Slope gradients usually range from 15 to 45%. Compare active slope (Hawley and Parsons, 1980).
metallic bond Bond resulting from the attraction of positively charge nuclei and valence electrons that can freely migrate among all the nuclei in a substance.
metamorphic rock Rock derived from preexisting rocks that have been altered physically, chemically, and/ or mineralogically as a result of natural geological processes, principally heat and pressure, originating within the earth. The preexisting rocks may have been igneous, sedimentary, or another form of metamorphic rock.
metasediment A sediment or sedimentary rock that shows evidence of having been subjected to metamorphism ( Jackson, 1997).
meteorite crater An impact crater formed by the falling of a large meteorite onto the earth’s surface; for example, Barringer Crater (AZ). Compare crater, impact crater (Schoeneberger and Wysocki, personal communication, 2013; Jackson, 1997).
mica A layer-structured aluminosilicate mineral group of the 2:1 type that is characterized by its nonexpandability and high layer charge, which is usually satisfied by potassium. The major types are muscovite, biotite, and phlogopite. Compare Appendix I, Table A3.
micorrhizosphere Unique microbial community that develops around a mycorrhiza.
micro-depression (not preferred) Use microlow.
micro-knoll (not preferred) use microhigh.
microaerophile An organism that requires a low concentration of oxygen for growth. Sometimes used to indicate an organism that will carry out its metabolic activities under aerobic conditions but that will grow much better under anaerobic conditions.
microbial population The sum of living microorganisms in a given volume or mass of soil.
microbial biomass (a) The total mass of living microorganisms in a given volume or mass of soil. (b) The total weight of all microorganisms in a particular environment.
microbiota Microflora and protozoa.
microbiotic crust A thin, surface layer (crust) of soil particles bound together primarily by living organisms and their organic byproducts; thickness can range up from < 1 cm up to 10 cm; aerial coverage of the ground surface can range from 10 to 100%. Crusts stabilize loose earthy material. Other types of surface crusts include chemical crusts (e.g., salt crusts) and physical crusts (e.g., raindrop-impact crust; Schoeneberger and Wysocki, personal communication, 2013; Summer and Stewart, 1992).
microclimate (a) The climatic condition of a small area resulting from the modification of the general climatic conditions by local differences in elevation or exposure or other local phenomena. (b) The sequence of atmospheric changes within a very small region.
microcline A potassium feldspar identical in composition to orthoclase but differing in internal structure. KAlSi3O8.
microcosm A community or other unit that is representative of a larger unit.
microfauna Protozoa, nematodes, and arthropods of microscopic size.
microfeature [soil survey] Small, local, natural forms (features) on the land surface that are too small to delineate on a topographic or soils map at commonly used map scales (e.g., 1:24,000 to 1:10,000). Examples include earth pillar, patterned ground, frost boil (Schoeneberger and Wysocki, personal communication, 2013). Compare microrelief.
microflora Bacteria (including actinomycetes), fungi, algae, and viruses.
microhabitat Clusters of microaggregates with associated water within which microorganisms function; may be composed of several microsites (i.e., aerobic and anaerobic).
microhigh A generic microrelief term applied to slightly elevated areas relative to the adjacent ground surface; differences in relief range from several centimeters to several meters. Cross-sectional profiles can be simple or complex and generally consist of gently rounded, convex tops with gently sloping sides; also spelled micro-high (Schoeneberger and Wysocki, personal communication, 2013). Compare microlow.
microirrigation Refer to irrigation, trickle.
microlow A generic microrelief term applied to slightly lower areas relative to the adjacent ground surface (e.g., shallow depression); differences in relief range from several centimeters to several meters. Cross-sectional profiles can be simple or complex and generally consist of subdued, concave, open or closed depressions with gently sloping sides; also spelled micro-low (Schoeneberger and Wysocki, personal communication, 2013).
micronutrient
A plant nutrient found in relatively small amounts (<100 mg kg-1) in plants. These are usually B, Cl, Cu, Fe, Mn, Mo, Ni, Co, and Zn.
micropore A class of pores that are sufficiently small that water within these pores is considered immobile, but available for plant extraction, and solute transport is by diffusion only (refer to pore-size classification).
microrelief (a) Slight variations in the height of a land surface that are too small to delineate on a topographic or soils map at commonly used map scales (e.g., 1:24,000 and 1:15,840). Examples include microhigh, micoslope, microlow (Schoeneberger and Wysocki, personal communication, 2013). Compare Microfeature. (b) (not preferred, refer to Microfeature). Generically refers to local, slight irregularities in form and height of a land surface that are superimposed upon a larger landform, including such features as low mounds, swales, and shallow pits ( Jackson, 1997). Compare gilgai, shrub-coppice dune, tree-tip mound, tree-tip pit.
microsite A small volume of soil where biological or chemical processes differ from those of the soil as a whole, such as an anaerobic microsite of a soil aggregate or the surface of decaying organic residues.
microslope A generic Microrelief term applied to areas of nominal surface relief (slightly sloping to level), relative to the adjacent ground surface; differences in overall local relief range from several centimeters to several meters. Cross-sectional profiles can be simple or complex and generally consist of low and gently rounded, convex tops (microhigh) with gently sloping to level sides (microslope), and depressional low areas (microlow). Microslopes commonly constitute the majority of the land surface in gilgai and other settings with microrelief (Schoeneberger and Wysocki, personal communication, 2013).
microsymbiont Usually refers to the prokaryotic partner in a nitrogen-fixing symbiosis.
midden A mound or stratum of refuse (broken pots, ashes, food remains, etc.) normally found on the site of an ancient settlement ( Jackson, 1997).
middlebreaking Refer to tillage, listing.
mima mound A term used for one of numerous low circular or oval domes composed of loose, unstratified, gravelly, silty, or sandy material. The basal diameter varies from 3 m to more than 30 m, and the height from 30 cm to about 2 m. Compare pimple mound, patterned ground, shrub-coppice dune ( Jackson, 1997).
mine spoil, metal-ore extraction Randomly mixed, earthy materials artificially deposited as a result of either surficial or underground metal-ore mining activities; a type of mine spoil (Schoeneberger and Wysocki, personal communication, 2013).
mine dumps Areas covered with overburden and other waste materials from ore and coal mines, quarries and smelters, and usually with little or no vegetative cover. Compare miscellaneous areas.
mine spoil or earthy fill [soil survey] An accumulation of displaced earthy material, rock, or other waste material removed during mining or excavation (Schoeneberger and Wysocki, personal communication, 2013).
mine spoil, coal extraction Randomly mixed, earthy materials artificially deposited as a result of either surficial or underground coal mining activities; a type of mine spoil (Schoeneberger and Wysocki, personal communication, 2013).
mineral A naturally occurring homogeneous solid, inorganically formed, with a definite chemical composition and an ordered atomic arrangement.
mineral soil
A soil consisting predominantly of, and having its properties determined predominantly by, mineral matter. Usually contains <200 g kg-1organic carbon (<120-180 g kg-1 if saturated with water), but may contain an organic surface layer up to 30 cm thick.
mineralization The conversion of an element from an organic form to an inorganic state as a result of microbial activity.
mineralogical analysis The estimation or determination of the kinds or amounts of minerals present in a rock or in a soil.
miner’s inch Refer to irrigation, miner’s inch.
minor elements Refer to micronutrients.
minor scarp A steep surface on the displaced material of a landslide, produced by differential movements within the sliding mass (Cruden and Varnes, 1996). Compare main scarp, toe.
Miocene An epoch of the Tertiary Period of geologic time (from approximately 5.3 million to 23.0 million years ago) that immediately follows the Oligocene and precedes the Pliocene Epoch; also the corresponding (time-stratigraphic) “series” of earth materials (Schoeneberger and Wysocki, personal communication, 2013).
miscellaneous areas A kind of land area having little or no soil and thus supporting little or no vegetation without major reclamation. Includes areas such as beaches, dumps, rock outcrop, and badlands. The term is used in defining soil survey map units.
miscible displacement The process that occurs when a fluid mixes with and displaces another fluid. Leaching salts from a soil is an example because the added water mixes with and displaces the soil solution.
mist irrigation Refer to irrigation.
mixed fertilizers Two or more fertilizer materials mixed or granulated together.
mixing Refer to tillage, mixing.
mobile water soil water zone that flows and transports solutes, subject to hydrodynamic dispersion.
modeling
advective-dispersive equation Refer to convection-dispersion equation.
modeling, analytical methods analytical methods (model) Use of classical mathematical approaches to solve complex formulas, such as differential equations, describing a soil process.
modeling, benchmarking benchmarking The process of comparing a model’s predictions to other “verified” codes to determine that model’s code is functioning properly.
modeling, boundary conditions A prescribed condition imposed upon the boundary of the flow domain.
modeling, calibration The adjusting of input parameters until model predictions match the observed response. This is performed by setting the majority of the parameters to measured values and adjusting only the few parameters that lack measurement or have the greatest uncertainty.
modeling, deterministic model Models based upon the concept that a discrete value exists for the variable of interest at each point in space and given a set of input values, a unique output can be determined.
modeling, Dirichlet condition A boundary condition where a value for the variable of interest at each point in space and given a set of input values, a unique output can be determined.
modeling, discretization The dividing of the flow domain into nodes or elements.
modeling, dynamic nonequilibrium Flow rate dependent hydraulic properties or local nonequilibrium not due to traditional hysteresis (Diamantopoulos et al., 2012).
modeling, empirical model Simple mathematical relationships derived from observations for describing more complex processes.
modeling, finite difference A numerical method in which the flow domain is discretized into nodal points such that the differential equations can be reformulated into a series of simple algebraic (finite difference) approximations.
modeling, finite element A numerical method that creates an integral form of the differential equation by discretizing the flow domain into a variety of element shapes.
modeling, flow domain Spatial representation of the physical environment being simulated.
modeling,dynamic nonequilibrium Flow rate dependent hydraulic properties or local nonequilibrium not due to traditional hysteresis (Diamantopoulos et al., 2012).
modeling,finite element A numerical method that creates an integral form of the differential equation by discretizing the flow domain into a variety of element shapes.
moder A type of forest humus transitional between mull and mor (term used mostly in Europe; also called duff mull in United States and Canada). Sometimes differentiated into the following groups: Mormoder, Leptomoder, Mullmoder, Lignomoder, Hydromoder, and Sapimoder.
moderately coarse textured Texture group consisting of coarse sandy loam, sandy loam, and fine sandy loam textures. Compare soil texture.
moderately fine textured Texture group consisting of clay loam, sandy clay loam, and silty clay loam textures. Compare soil texture.
moderately well drained A drainage class referring to soils which have evidence (e.g., mottles) of seasonal water tables at depths between 46 and 91 cm (18 and 36 in).
mogote (colloquial: Caribbean Basin) An isolated, steep-sided, commonly asymmetrical hill or ridge composed of limestone, generally steeper on its leeward side (prevailing downwind side) and surrounded by nearly level to sloping coastal plain composed of marine and alluvial sediments; a type of karst tower. They range in height from a few feet (< 1 m) to over 150 ft (50 m). Most are isolated and cover small areas but some form clusters of hills or ridges rising out of the surrounding blanket deposits. Mogotes are extensive in northern Puerto Rico (Monroe, 1976, 1980; Schoeneberger and Wysocki, personal communication, 2013; White, 1988).
Mohr circle of stress A graphical representation of the components of stress acting across the various planes at a given point, drawn with reference to axes of normal stress and shear stress.
Mohr envelope The envelope of a series of Mohr circles representing stress conditions at failure for a given material.
moisture state classes Refer to soil moisture regimes.
moisture equivalent (no longer used in SSSA publications) The weight percentage of water retained by a previously saturated sample of soil 1 cm in thickness after it has been subjected to a centrifugal force of one thousand times gravity for 30 min.
moisture-release curve (no longer used in SSSA publications) Refer to soil water.
moisture-retention curve Refer to soil water characteristic or characteristic curve.
moldboard plowing Refer to tillage, plowing.
mollic epipedon
[soil taxonomy] A surface horizon of mineral soil that is dark colored and relatively thick, contains at least 5.8 g kg-1 organic carbon, is not massive and hard or very hard when dry, has a base saturation of>50% when measured at pH 7, has <110 mg P kg-1 soluble in 0.05 M citric acid, and is dominantly saturated with divalent cations (USDA, 1999).
Mollisols [soil taxonomy] An order of very dark colored, base-rich mineral soils that have a mollic epipedon that commonly overlies mineral material with a base saturation of 50% or more (measured at pH 7). Mollisols may have an argillic, natric, calcic, or less commonly an albic, or petrocalcic horizon, a histic epipedon, or a duripan, but not an oxic or spodic horizon. Mollisols may have any temperature regime but do not have permafrost.
monadnock An isolated hill or mountain of resistant rock rising conspicuously above the general level of a lower erosion surface in a temperate climate representing an isolated remnant of a former erosion cycle in an area that has largely been beveled to its base level ( Jackson, 1997). Compare inselberg, nunatak.
monocline [landform] A unit of folded strata that dips from the horizontal in one direction only, is not part of an anticline or syncline, and occurs at the earth’s surface. This structure is typically present in plateau areas where nearly flat strata locally assume steep dips caused by differential vertical movements without faulting (Schoeneberger and Wysocki, personal communication, 2013; Hawley and Parsons, 1980). Compare anticline, syncline, fold.
monofractals Refer to fractal, monofractals.
montmorillonite Si4Al1.5Mg0.5O10(OH)2Ca0.25 An aluminum silicate (smectite) with a 2:1 layer structure composed of two silica tetrahedral sheets and a shared aluminum and magnesium octahedral sheet. Montmorillonite has a permanent negative charge that attracts interlayer cations that exist in various degrees of hydration thus causing expansion and collapse of the structure (i.e., shrink-swell). The calcium in the formula above is readily exchangeable with other cations. Compare Appendix I, Table A3.
montmorillonite-saponite group obsolete; replaced by smectite. Compare phyllosilicate mineral terminology.
mor A type of forest humus characterized by an accumulation of organic matter on the soil surface in matted Oe(F) horizons, reflecting the dominant mycogenous decomposers. The boundary between the organic horizon and the underlying mineral soil is abrupt. Sometimes differentiated into the following groups: Hemimor, Humimor, Resimor, Lignomor, Hydromor, Fibrimor, and Mesimor.
moraine (a) [material] A mound, ridge, or other topographically distinct accumulation of unsorted, unstratified drift, predominantly till, deposited primarily by the direct action of glacial ice. (b) [landform] A general term for a landform composed mainly of till that has been deposited by a glacier; a kame moraine is a type of moraine similar in exterior form to other types of moraines but composed mainly of stratified outwash materials. Examples are disintegration, end, ground, kame, lateral, recessional, and terminal moraines.
mosaic, aerial An assemblage of overlapping aerial or space photographs or images whose edges have been matched to form a continuous pictorial representation of a portion of the earth’s surface.
moss peat [soil taxonomy] An accumulation of organic material that is predominantly the remains of mosses (e.g., sphagnum moss). Compare herbaceous peat, sedimentary peat, woody peat, peat, muck, and mucky peat (Soil Survey Staff, 1993).
mossy organic materials Refer to organic materials.
most probable number A method for estimating microbial numbers in soil based on dilution to extinction.
mottled zone A layer that is marked with spots or blotches of different color or shades of color. The pattern of mottling and the size, abundance, and color contrast of the mottles may vary considerably and should be specified in soil description.
mottles Spots or blotches of different color or shades of color interspersed with the dominant color. In 1998, the definition was changed to no longer include blotches of color associated with redoximorphic conditions (called redoximorphic features; USDA, 1999). Such color bodies are now due solely to lithochromic sources (e.g., natural color of the parent material).
mound (a) A low, rounded natural hill of unspecified origin, generally < 3 m high and, composed of earthy material; (b) A small, human-made hill, composed either of debris accumulated during successive occupations of the site (e.g., tell) or of earth heaped up to mark a burial site (e.g., burial mound). (c) A structure built by colonial organisms (e.g., termite mound; Jackson, 1997).
mountain A generic term for an elevated area of the land surface, rising more than 300 m above surrounding lowlands, usually with a nominal summit area relative to bounding slopes and generally with steep sides (greater than 25% slope) with or without considerable bare-rock exposed. A mountain can occur as a single, isolated mass or in a group forming a chain or range. Mountains are primarily formed by tectonic activity and/or volcanic action and secondarily by differential erosion (Schoeneberger and Wysocki, personal communication, 2013; Hawley and Parsons, 1980). Compare hill, hillock, plateau, foothills, mountains.
mountain system A group of mountain ranges exhibiting certain unifying features, such as similarity in form, structure and alignment, and presumably originating from the same general causes; especially a series of mountain ranges belonging to an orogenic belt ( Jackson, 1997). Compare mountain range, mountains.
mountain range A single, large mass consisting of a succession of mountains or narrowly spaced mountain ridges, with or without peaks, closely related in position, direction, orientation, formation, and age; a component part of a mountain system ( Jackson, 1997). Compare mountain system, mountains.
mountain slope A part of a mountain between the summit and the foot ( Jackson, 1997). Compare mountainflank, hillslope.
mountain valley (a) Any small, externally drained V-shaped depression (in cross-section) cut or deepened by a stream and floored with alluvium, or a broader, U-shaped depression modified by an alpine glacier and floored with either till or alluvium, that occurs on a mountain or within mountains. Several types of mountain valleys can be recognized based on their form and valley floor sediments (i.e., V-shaped valley, U-shaped valley). Compare valley (Schoeneberger and Wysocki, personal communication, 2013). (b) (colloquial: Basin and Range, USA) A relatively small, structural depression within a mountain range that is partly filled with alluvium and commonly drains externally to an intermontane basin, bolson, or semi-bolson (Schoeneberger and Wysocki, personal communication, 2013; Peterson, 1981). Compare valley flat.
mountainbase A geomorphic component of mountains consisting of the lowermost area, consisting of the strongly to slightly concave colluvial apron or wedge at the bottom of mountain slopes; composed of long-transport colluvium and slope alluvium sediment. It can extend out onto more level valley areas where it ultimately interfingers with, is buried by alluvium or is replaced by re-emergent residuum (Schoeneberger and Wysocki, personal communication, 2013). Compare mountaintop, mountainflank, free face, geomorphic component.
mountainflank A geomorphic component of mountains consisting of the side area of mountains, characterized by very long, complex backslopes with comparatively high slope gradients and composed of highly-diverse, colluvial sediment mantles, complex near-surface hydrology, mass movement processes and features (e.g., creep, landslides); rock outcrops or structural benches may be present. The mountainflank can be subdivided by the general location along the mountainside (i.e., upper third, middle third, or lower third mountainflank; Schoeneberger and Wysocki, personal communication, 2013). Compare mountaintop, mountainbase, free face, geomorphic component.
mountains A region or landscape characterized by mountains and their intervening valleys; a generic name for any group, cluster, or sequence of mountains or narrowly spaced mountain ridges, with or without peaks, closely related in position, orientation, direction, formation, or age, and whose summits commonly exceed 300 m (approx. 1000 ft; Schoeneberger and Wysocki, personal communication, 2013). Compare foothills, hills, mountain range, mountain system.
mountainside (not recommended) use mountain slope.
mountaintop A geomorphic component of mountains consisting of the uppermost, comparatively level or gently sloped area of mountains, characterized by relatively short, simple slopes composed of bare rock, residuum, or short-transport colluvial sediments. In humid environments, mountaintop soils can be quite thick and well developed (Schoeneberger and Wysocki, personal communication, 2013). Compare mountainflank, mountainbase, free face, geomorphic component.
mucigel The gelatinous material at the surface of roots grown in nonsterile soil. It includes natural and modified plant exudates (more specifically mucilages), bacterial cells, and their metabolic products (e.g., capsules and slimes), as well as colloidal mineral and organic matter from the soil.
muck Unconsolidated, highly decomposed organic soil material in which the original plant parts are not recognizable (i.e., “sapric” in soil taxonomy). It generally contains more mineral matter and is usually darker in color than peat. Compare herbaceous muck, mucky peat, muck soil, peat, peat soil, and sapric material.
muck soil An organic soil in which the plant residues have been altered beyond recognition. The sum of the thicknesses of organic layers is usually greater than the sum of the thicknesses of mineral layers.
mucky peat Organic soil material in an intermediate state of decomposition such that a significant part of the original plant parts is recognizable and a significant part is not (i.e., “hemic” in soil taxonomy; Soil Survey Staff, 1993). Compare herbaceous peat, peat and muck.
mud flat (not preferred; use tidal flat) A relatively level area of fine grained material (e.g., silt) along a shore (as in a sheltered estuary) or around an island, alternately covered and uncovered by the tide or covered by shallow water, and barren of vegetation ( Jackson, 1997). Compare low marsh, tidal flat, tidal marsh.
mud pot A type of hot spring containing boiling mud, usually sulfurous and often multicolored, as in a paint pot. Mud pots are commonly associated with geysers and other hot springs in volcanic areas, especially in Yellowstone National Park, WY ( Jackson, 1997). Compare geyser, hot spring.
mudflow [mass movement] The process, associated sediments (mudflow deposit) or resultant landform characterized by a very rapid type of earthflow dominated by a sudden, downslope movement of a saturated mass of rock, soil, and mud (more than 50% of the particles are <2 mm), that behaves much as a viscous fluid when moving. If more than half of the solid fraction consists of material larger than sand size, debris flow is preferred (Schoeneberger and Wysocki, personal communication, 2013; Varnes, 1978). Compare flow, landslide.
mudstone (a) A blocky or massive, fine-grained sedimentary rock in which the proportions of clay and silt are approximately equal; (b) A general term that includes clay, silt, claystone, siltstone, shale, and argillite, and that should be used only when the amounts of clay and silt are not known or cannot be precisely identified ( Jackson, 1997).
mulch Refer to tillage, mulch.
mulch farming Refer to tillage, mulch farming.
mull A forest humus type characterized by intimate incorporation of organic matter into the upper mineral soil (i.e., a well-developed A horizon) in contrast to accumulation on the surface. (Sometimes differentiated into the following groups: Vermimull, Rhizomull, and Hydromull.)
multifractals Refer to fractal, multifractal.
multilevel sampling Collecting remotely sensed data from different types of platforms with ground data from the same geographic area.
multispectral Generally used for remote sensing in two or more spectral bands, such as visible and infrared.
Munsell color system A color designation system widely used to describe soil color that specifies the relative degrees of the three simple variables of color: hue, value, and chroma. For example: 10YR 6/4 is a color (of soil) with a hue = 10YR, value = 6, and chroma = 4. Compare chroma, hue, value, color.
muscovite A clear, dioctahedral layer silicate of the mica group with Al3+ in the octahedral layer and Si and Al in a ratio of 3:1 in the tetrahedral layer. Compare Appendix I, Table A3.
muskeg A bog, usually a sphagnum bog, frequently with grassy tussocks (hummocks), growing in wet, poorly drained boreal regions, with deep accumulations of organic material, often in areas of permafrost; a moss-covered muck or peat bog of boreal regions ( Jackson, 1997; Hawley and Parsons, 1980). Compare peatland.
mutualism Refer to symbiosis.
mycelium A mass of interwoven filamentous hyphae, such as that of the vegetative portion of the thallus of a fungus.
myco Prefix designating an association or relationship with a fungus (e.g., mycotoxins are toxins produced by a fungus).
mycophage Soil virus that infects a fungus.
mycorrhiza (pl. mycorrhizae) Literally “fungus root.” The association, usually symbiotic, of specific fungi with the roots of higher plants. Compare endomycorrhiza and ectomycorrhiza.