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.
made land: Areas filled with earth, or with earth and trash mixed, usually by or under the control of man.
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.
marl: Soft and unconsolidated calcium carbonate, usually mixed with varying amounts of clay or other impurities.
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.
mass flow (nutrient): The movement of solutes associated with net movement of water.
mass movement: 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.
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.
meander land: 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.
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.
mesic: 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.
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.
microbial biomass: (i) The total mass of living microorganisms in a given volume or mass of soil. (ii) The total weight of all microorganisms in a particular environment.
microclimate: (i) 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. (ii) The sequence of atmospheric changes within a very small region.
mineralization: The conversion of an element from an organic form to an inorganic state as a result of microbial activity.
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.
moder: A type of forest humus transitional between mull and mor. Sometimes differentiated into the following groups: Mormoder, Leptomoder, Mullmoder, Lignomoder, Hydromoder, and Sapimoder.
mollic epipedon: A surface horizon of mineral soil that is dark colored and relatively thick, contains at least 5.8 g kg-1organic 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-1soluble in 0.05 M citric acid, and is dominantly saturated with divalent cations.
Mollisols: Mineral soils that have a mollic epipedon overlying mineral material with a base saturation of 50% or more when measured at pH 7. Mollisols may have an argillic, natric, albic, cambic, gypsic, calcic, or petrocalcic horizon, a histic epipedon, or a duripan, but not an oxic or spodic horizon.
mor: A type of forest humus characterized by an accumulation or 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: An accumulation of drift, with an initial topographic expression of its own, built chiefly by the direct action of glacial ice. Examples are end, ground, 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.
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.
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: Organic soil material in which the original plant parts are not recognizable. Contains more mineral matter and is usually darker in color than peat.
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 which a significant part of the original plant parts are recognizable and a significant part is not.
mudflow: A general term for a mass movement landform and a process characterized by a flowing mass of predominantly fine-grained earth material (particles less than 2 mm comprising more than 50 percent of the solid material) possessing a high degree of fluidity during movement. If more than half of the solid fraction consists of material larger than sand size, debris flow is preferred.
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).
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).
mycorrhiza (pl. mycorrhizae): Literally "fungus root". The association, usually symbiotic, of specific fungi with the roots of higher plants.n-value: The relationship between the percentage of water under field conditions and the percentages of inorganic clay and of humus.
natric horizon: A mineral soil horizon that satisfied the requirements of an argillic horizon, but that also has prismatic, columnar, or blocky structure and a subhorizon having >15% saturation with exchangeable Na+.
natural levee: A long, broad low ridge or embankment of sand and coarse silt, built up by a stream on its flood plain and along both sides of its channel. They are wedge-shaped deposits, of the coarsest suspended-load material, that slope gently away from the stream.
neocutan: A cutan with a consistent relationship with natural surfaces of soil material. It does not occur immediately at the surfaces. Similar to hypo-coating.
neutral soil: A soil in which the surface layer, at least in the tillage zone, is in the pH 6.6 to 7.3 range.
niche: (i) The particular role that a given species plays in the ecosystem; (ii) The physical space occupied by an organism.
nitrate reduction (biological): The process whereby nitrate is reduced by plants and microorganisms to ammonium for cell synthesis (nitrate assimilation, assimilatory nitrate reduction) or to nitrite by bacteria using nitrate as the terminal electron acceptor in anaerobic respiration (respiratory nitrate reduction, dissimilatory nitrate reduction). Sometimes used synonymously with "denitrication."
nitrification: Biological oxidation of ammonium to nitrite and nitrate, or a biologically induced increase in the oxidation state of nitrogen.
nodule: (i) A cemented concentration of a chemical compound, such as calcium carbonate or iron oxide, that can be removed from the soil intact and that has no orderly internal organization. (ii) [micromorphological] A glaebule with undifferentiated fabric. (iii) Specialized tissue enlargements, or swellings, on the roots, stems, or leaves of plants, such as are caused by nitrogen-fixing microorganisms.
nonlimiting water range: The region bounded by the upper and lower soil water content over which water, oxygen, and mechanical resistance are not limiting to plant growth. Compare with available water.
nutrient: Elements or compounds essential as raw materials for organism growth and development.ochric epipedon: A surface horizon of mineral soil that is too light in color, too high in chroma, too low in organic carbon, or too thin to be a plaggen, mollic, umbric, anthropic or histic epipedon, or that is both hard and massive when dry.
oil wasteland: Areas on which liquid oily wastes, principally saltwater and oil, have accumulated. Includes slush pits and adjacent areas affected by oil waste. A miscellaneous area.
organan: A cutan composed of a concentration of organic matter.
organic farming: Crop production system that reduces, avoids or largely excludes the use of synthetically compound fertilizers, pesticides, growth regulators, and livestock feed additives.
organic fertilizer: By product from the processing of animals or vegetable substances that contain sufficient plant nutrients to be of value as fertilizers.
organic soil: A soil in which the sum of the thicknesses of layers containing organic soil materials is generally greater than the sum of the thicknesses of mineral layers.
ortstein: A cemented spodic horizon.
oven-dry soil: Soil that has been dried at 105°C until it reaches constant mass.
oxic horizon: A mineral soil horizon that is at least 30 cm thick and characterized by the virtual absence of weatherable primary minerals or 2:1 layer silicate clays, the presence of 1:1 layer silicate clays and highly insoluble minerals such as quartz sand, the presence of hydrated oxides of iron and aluminum, the absence of water-dispersible clay, and the presence of low cation exchange capacity and small amounts of exchangeable bases.
oxidation: The loss of one or more electrons by an ion or molecule.
oxidative phosphorylation: Conversion of inorganic phosphate into the energy-rich phosphate of adenosine 5'-triphosphate.
Oxisols: Mineral soils that have an oxic horizon within 2 m of the surface or plinthite as a continuous phase within 30 cm of the surface, and that do not have a spodic or argillic horizon above the oxic horizon.
paleosol: A soil that formed on a landscape in the past with distinctive morphological features resulting from a soil-forming environment that no longer exists at the site. The former pedogenic process was either altered because of external environmental change or interrupted by burial. A paleosol (or component horizon) may be classed as relict if it has persisted in a land-surface position without major alteration of morphology by processes of the prevailing pedogenic environment. An exhumed paleosol is one that formerly was buried and has been re-exposed by erosion of the covering mantle.
papule: Glaebule composed dominantly of clay minerals with continuous and/or lameliar fabric, and sharp external boundaries.
parent material: The unconsolidated and more or less chemically weathered mineral or organic matter from which the solum of soils is developed by pedogenic processes.
pasteurization: Partial sterilization of soil, liquid, or other natural substances by temporary heat treatment.
patterned ground: A general term for any ground surface exhibiting a discernibly ordered, more-or-less symmetrical, morphological pattern of ground and, where present, vegetation. Patterned ground is characteristic of, but not confined to, permafrost regions or areas subjected to intense frost action; it also occurs in tropical, subtropical, and temperate areas. Patterned ground is classified by type of pattern and presence or absence of sorting and includes nonsorted and sorted circles, net, polygons, steps and stripes, garlands, and solifluction features. In permafrost regions, the most common macroform is the ice-wedge polygon and a common microform is the nonsorted circle.
peat: Organic soil material in which the original plant parts are recognizable (fibric material).
peat soil: An organic soil in which the plant residues are recognizable. The sum of the thicknesses of the organic layers are usually greater than the sum of the thicknesses of the mineral layers.
pebbles: Rounded or partially rounded rock or mineral fragments between 2 and 75 mm in diameter. Size may be further refined as fine pebbles (2-5 mm diameter), medium pebbles (5-20 mm diameter), and coarse pebbles (20-75 mm diameter).
pedal: Applied to soil materials, most of which consists of peds.
pedalfer: A subdivision of a soil order comprising a large group of soils in which sesquioxides increased relative to silica during soil formation.
pediment: A gently sloping, erosional surface developed at the foot of a receding hill or mountain slope. The surface can be bare or it may be thinly mantled with alluvium and colluvium in transport to the adjacent valley.
pedisediment: A layer of sediment, eroded from the shoulder and back slope of an erosional slope, that lies on and is, or was, being transported across a pediment.
pedoturbation: Mixing within a soil or sediment profile by various processes, such as animal burrowing, tree throw, freeze-thaw cycles, etc. It usually involves disturbance of the skeletal fabric as opposed to redistribution of only the fine particles.
peneplain: An area which has been reduced by erosion to a low, gently rolling surface resembling a plain.
pergelic: A soil temperature regime that has mean annual soil temperatures of <0°C. Permafrost is present.
periglacial: Pertaining to processes, conditions, areas, climates, and topographic features occurring at the immediate margins of glaciers and ice sheets, and influenced by cold temperature of the ice.
permafrost: (i) Permanently frozen material underlying the solum. (ii) A perennially frozen soil horizon.
permeability, soil: (i) The ease with which gases, liquids, or plant roots penetrate or pass through a bulk mass of soil or a layer of soil. Since different soil horizons vary in permeability, the particular horizon under question should be designated. (ii) The property of a porous medium itself that expresses the ease with which gases, liquids, or other substances can flow through it, and is the same as intrinsic permeability k.
petrocalcic horizon: A continuous, indurated calcic horizon that is cemented by calcium carbonate and, in some places, with magnesium carbonate. It cannot be penetrated with a spade or auger when dry, dry fragments do not slake in water, and it is impenetrable to roots.
petroferric contact: A boundary between soil and a continuous layer of indurated soil in which iron is an important cement. Contains little or no organic matter.
petrogypsic horizon: A continuous, strongly cemented, massive, gypsic horizon that is cemented by calcium sulfate. It can be chipped with a spade when dry. Dry fragments do not slake in water and it is impenetrable to roots.
phosphate: In fertilizer trade terminology, phosphate is used to express the sum of the water-soluble and the citrate-soluble phosphoric acid (P2O5); also referred to as the available phosphoric acid (P2O5).
phyllosphere: The surface of above-ground living plant parts.
physiosorption: The process of attachment of non-ionic substances such as polar water molecules, acetic acid molecules, or nucleic acids to clays or to other solid-phase surfaces. The attachment of large molecules to clay particles by ionic processes is not physiosorption.
phytotoxic: The property of a substance at a specified concentration that restricts or constrains plant growth.
pits: Open excavations from which soil and commonly, underlying material, have been removed exposing either rock or other material that supports few or no plants. Includes mine pits, gravel pits, and quarry pits. A miscellaneous area.
placic horizon: A black to dark reddish mineral soil horizon that is usually thin but that may range from 1 mm to 25 mm in thickness. The placic horizon is commonly cemented with iron and is slowly permeable or impenetrable to water and roots.
plaggen epipedon: A man-made surface horizon more than 50 cm thick that is formed by long-continued manuring and mixing.
plain: A flat, undulating, or even rolling area, larger or smaller, that includes few prominent hills or valleys, that usually is at low elevation in reference to surrounding areas, and that may have considerable overall slope and local relief.
Planosol: A great soil group of the intrazonal order and hydromorphic suborder consisting of soils with eluviated surface horizons underlain by B horizons more strongly eluviated, cemented, or compacted than associated normal soil.
playa: An ephemerally flooded, vegetatively barren area on a basin floor that is veneered with fine-textured sediment and acts as a temporary or as the final sink for drainage water.
plinthite: A weakly-cemented iron-rich, humus poor mixture of clay with other diluents that commonly occurs as dark red redox concentrations that form platy, polygonal, or reticulate patterns. Plinthite changes irreversibly to ironstone hardpans or irregular aggregates on exposure to repeated wetting and drying.
pocosin: A swamp, usually containing organic soil, and partly or completely enclosed by a sandy rim. The Carolina Bays of the Southeastern USA.
Podzol: A great soil group of the zonal order consisting of soils formed in cool-temperate to temperate, humid climates, under coniferous or mixed coniferous and deciduous forest, and characterized particularly by a highly-leached, whitish-gray (Podzol) horizon.
podzolization: A process of soil formation resulting in the genesis of Podzols and Podzolic soils.
porosity: The volume of pores in a soil sample (nonsolid volume) divided by the bulk volume of the sample.
potassium fixation: The process of converting exchangeable or water-soluble potassium to that occupying the position of K+ in the micas. They are counter-ions entrapped in the ditrigonal voids in the plane of basal oxygen atoms of some phyllosilicates as a result of contraction of the interlayer space. The fixation may occur spontaneously with some minerals in aqueous suspensions or as a result of heating to remove interlayer water in others. Fixed K+ ions are exchangeable only after expansion of the interlayer space.
precipitation interception: The stopping, interrupting, or temporary holding of descending precipitation in any form by mulch, a vegetative canopy, vegetation residue or any other physical barrier.
preferential flow: The process whereby free water and its constituents move by preferred pathways through a porous medium. Also called bypass flow.
priming effect: Stimulation of microbial activity in soil, usually organic matter decomposition, by the addition of labile organic matter.
prismatic soil structure: A shape of soil structure.
productivity, soil: The output of a specified plant or group of plants under a defined set of management practices.
profile, soil: A vertical section of the soil through all its horizons and extending into the C horizon.
proximal: Said of a sedimentary deposit consisting of coarse clastics and deposited nearest the source area.
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