Glossary of Terms in Soil Science

macronutrient

A chemical element necessary in large amounts, usually greater than 1 ppm in the plant, for the growth of plants and usually applied artificially in fertilizer or liming materials. Macro refers to the quantity and not to the essentiality of the element to the plant.

macroscopic velocity

See flow velocity.

made land

Areas filled with earth, or earth and trash mixed, usually by or under the control of man. A miscellaneous land type.

management / soil

(1) The total of all tillage operations, cropping practices, fertilizer, lime, and other treatments conducted on or applied to a soil for the production of plants. (2) The division of soil science dealing with the items listed in 1.

management groups / soil

Groups of soil units having similar adaptations or management requirements for one or more specific purposes such as adapted crops or crop rotations, drainage practices, fertilization, forestry and highway engineering.

manure

The excreta of animals with or without the admixture of bedding or litter in varying stages of decomposition. It is also called barnyard manure or stable manure. This is the usual meaning in North America. In some countries manure is used to refer to any fertilizer.

map / soil (Pedology)

A map showing the distribution of soil types or other soil mapping units related to the prominent physical and cultural features of the earth's surface. Descriptions of five kinds of soil maps follow:

detailed soil map (carte pédologique détaillée)
A soil map showing the boundaries between soil types or complexes of intimately associated soil types. The scale of the map depends on the purpose of the map, the intensity of land use, the pattern of soils, and the scale of other cartographic materials available. Traverses are usually made at 1/2-km (1/4-mile) intervals, or more frequently. The scale commonly used for field mapping is l:10,000 to 1:25,000.
detailed reconnaissance soil map (carte pédologique de reconnaissance détaillée)
A map showing the distribution of soils and physical features as determined by traversing the area at intervals of 1 to 2 km ( 'M2 to 1 mile). The scale, depending on the detail required, is 1:50,000 to 1:125,000.
generalized soil map (carte pédologique de généralisation)
A small-scale soil map showing the general distribution of soils within a large area in less detail than on a detailed soil map.
reconnaissance soil map (carte pédologique de reconnaissance)
A map, with less detail than the detailed reconnaissance map, showing the general distribution of soils determined by traverses at intervals of 2 to 4 km (1 to 2 miles). The scale is generally 1:125,000 to 1:250,000.
schematic soil map (carte pédologique schématique)
A soil map compiled from scant knowledge of the soils of new and undeveloped regions by applying available information about the soil-formation factors of the area. The scale is usually 1:500,000 or smaller. See also soil-formation factors.

map unit

Map unit is a generalization concept used in soil mapping to identify polygons with similar combinations of soils and landscapes. Each map unit consists of one or more polygons on a soil map. The degree of generalization employed when developing map units is the soil surveyor's perogative, and varying degrees of generalization were employed when mapping Canada's land resources.

marl

A soft, unconsolidated earthy deposit consisting of calcium carbonate or magnesium carbonate, or both, and often shells, usually mixed with varying amounts of clay or other impurities.

marsh

Periodically flooded or continually wet areas having the surface not deeply submerged. It is covered dominantly with sedges, cattails, rushes, or other hydrophytic plants. Subclasses include freshwater and saltwater marshes. See also swamp.

mass wasting

A general term for a variety of processes by which large masses of earth material are moved by gravity from one place to another.

matric potential

See water / soil.

matrix; soil

The main soil constituent or material that encloses other soil features, for example, concretions embedded in a fine-grained matrix.

mature soil

A soil having well-developed soil horizons produced by the natural processes of soil formation.

maximum water-holding capacity

The average moisture content of a disturbed sample of soil 1 cm high that is at equilibrium with a water table at its lower surface.

mechanical analysis

See particle-size analysis and particle-size distribution.

mechanics and engineering / soil

The subspecialization of soil science dealing with the effect of forces on the soil and the application of engineering principles to problems involving the soil.

medium texture

Intermediate between fine-textured and coarse-textured soils. It includes the following textural classes: very fine sandy loam, loam, silt loam and silt.

Melanic Brunisol

A great group of soils in the Brunisotic order. The soils have mull Ah horizons thicker than 5 cm (2 inches) and base-saturated Bm horizons. This group includes soils formerly classified as Brown Forest.

mellow soil

A very soft and very friable and porous soil having no tendency toward hardness or harshness. See also consistence.

mesa

A rather flat-topped, steep-sided hill or mountain that is usually composed of nearly horizontal strata of bedrock.

mesic layer

A layer of organic material at a stage of decomposition between that of the fibric and humic layers.

Mesisol

A great group of soils in the Organic order that are saturated for most of the year. The soils have a dominantly mesic middle tier, or middle and surface tiers if a terric, lithic, hydric, or cryic contact occurs in the middle tier.

mesophile

An organism growing best at moderate temperatures of 25 to 40°C.

metamorphic rock

Rock derived from preexisting rocks but differing from them in physical, chemical and mineralogical properties 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.

mica

A mineral group consisting of phyllosilicates having sheetlike 2:1 lattice structures generally with potassium in the interlayer position.

microaerophile

A microorganism growing best in the presence of small amounts of atmospheric oxygen.

microbiology / soil

The subspecialization of soil science dealing with soil-inhabiting microorganisms and their relationship to agriculture including both plant and animal growth.

microclimate

(1) The climate of a small area resulting from the modification of the general climate by local differences in elevation or exposure. (2) The sequence of atmospheric changes within a very small region.

microfauna

The part of the animal population consisting of individuals that are too small to be clearly distinguished without the use of a microscope. It includes protozoa and nematodes.

microflora

The part of the plant population consisting of individuals that are too small to be clearly distinguished without the use of a microscope. It includes algae and bacteria and fungi.

micronutrient

A chemical element necessary in only small amounts usually less than 1 ppm in the plant and for the growth of plants and the health of animals. Examples of these elements are boron, molybdenum, copper, iron, manganese and zinc. ""Micro"" refers to the amount, not the essentiality of the element to the organism. See also macronutrient.

microorganism

A form of life of microscopic size.

microrelief

microrelief Small-scale, local differences in relief, including mounds, swales, or hollows. See also cradle knoll and gilgai.

midden

A refuse heap marking the site of previous habitation.

mine dump

Area covered with overburden and other waste materials from ore and coal mines, quarries, and smelters, and usually having little or no vegetative cover. A miscellaneous land type.

mine wash

Water-deposited accumulations of sandy, silty, or clayey material recently eroded in mining operations. It may clog streams and channels, and damage land on which it is deposited. A miscellaneous land type.

mineral

A homogeneous naturaily occurring phase, sometimes restricted to inorganic, crystalline phases.

mineral (soil )

mineral, soil (1) Any mineral occurring as a part of or in the soil. (2) A natural inorganic compound with definite physical, chemical, and crystalline properties (within the limits of isomorphism) occurring in the soil. See also clay mineral.

mineral soil

A soil consisting predominantly of, and having its properties determined predominantly by, mineral matter. It contains less than 17% organic carbon except for an organic surface layer that may be up to 40 cm (16 inches) thick if formed of mixed peat (bulk density 0.1 or more) or 60 cm (24 inches) if of fibric moss peat (bulk density less than 0.1).

mineralization

The conversion of an element from an organic form to an inorganic state as a result of microbial decomposition.

mineralogical analysis

The estimation or determination of the kinds or amounts of minerals present in a rock or a soil.

mineralogy /soil

The subspecialization of soil science dealing with the homogeneous inorganic materials found in the earth's crust to the depth of weathering or sedimentation.

minor element

See micronutrient.

miscellaneous land type

A mapping unit for areas of land that have little or no natural soil or that are inaccessible for orderly examination or where for some reason it is not feasible to classify the soil. For example rough mountainous land, eroded slopes and marshes.

moder

A zoogenous forest humus form made up of plant remains partly disintegrated by the soil fauna (F layer) but not matted as in raw humus. It is transitional to a zone of spherical or cylindrical microdejections of arthropods that is permeated by loose mineral particles in its lower part and often throughout. Although incorporation of organic matter is intense it is shallow because none of the organisms concerned with moder formation have important burrowing activity. The mixing of organic and mineral particles is purely mechanical. Organic carbon under the F layer varies from 23% to 29%, but may exceed 35%. The C:N ratio is 20 to 25 and sometimes lower. Various subgroups can be recognized by their morphoiogy and chemical characteristics.

moderately coarse texture

Consisting predominantly of coarse particles. In soil textural classification it includes all the sandy loams except the very fine sandy loam. See also coarse texture

moderately fine texture

Consisting predominantly of intermediate-sized soil particles with or without small amounts of fine or coarse particles. In soil textural classification, it includes clay loam, sandy clay loam and silty clay loam. See also fine texture.

moisture (soil)

Water contained in the soil.

moisture equivalent

The weight percentage of water retained by a previously saturated sample of soil 1 cm thick after it has been subjected to a centrifugal force of 1000 times gravity for 30 min.

moisture tension / soil

In soils partially saturated with water there is moisture tension, which is equal in magnitude but opposite in sign to the soil water pressure. Moisture tension is equal to the pressure that must be applied to the soil water to bring it to a hydraulic equilibrium, through a porous permeable wall or membrane, with a pool of water of the same composition.

The pressures used and the corresponding percentages most commonly determined are:

15-atmosphere percentage (pourcentage à atmosphères)
The percentage of water contained in a soil that has been saturated, subjected to, and is in equilibrium with, an applied pressure of 15 atm. Pressure is applied in a pressure membrane or ceramic pressure plate apparatus. It is usually expressed as a weight percentage, but may be expressed as a volume percentage. It is approximately the same as 15-bar percentage.
15-bar percentage (pourcentage à 15 bars)
The percentage of water contained in a soil that has been saturated, subjected to, and is in equilibrium with an applied pressure of 15 bars. Pressure is applied in a pressure membrane or ceramic plate apparatus. It is usually expressed as a weight percentage, but may be expressed as a volume percentage. It is approximately the same as 15-atmosphere percentage.
1/3-atmosphere percentage (pourcentage à 1/3 atmosphères)
The percentage of water contained in a soil that has been saturated, subjected to, and is in equilibrium with an applied pressure of l/3 atm. Pressure is applied in a ceramic plate apparatus. It is usually expressed as a weight percentage, but may be expressed as a volume percentage. It is approximately the same as l/3-bar percentage. Also, for medium- to coarse-textured soils it is approximately numerically equal to moisture equivalent.
1/3-bar percentage (pourcentage à 1/3 bar)
The percentage of water contained in a soil that has been saturated, subjected to, and is in equilibrium with an applied pressure of l/3 bar. Pressure is applied in a ceramic plate apparatus. It is usually expressed as a weight percentage and is approximately the same as l/3-atmosphere percentage. Also, for medium- to coarse-textured soils it is approximately numerically equal to moisture equivalent.
60-centimetre percentage (pourcentage à 60 centimètres)
The percentage of water contained in a soil that has been saturated, subjected to, and is in equilibrium with an applied pressure or tension equivalent to a column of water 60 cm high. Pressure may be applied in a pressure plate apparatus or, as a tension, on a tension table. It may be expressed on a weight or volume basis and is considered by many to approximate the "field capacity," especially in medium- to coarse-textured soils.

moisture-release curve

See moisture-retention curve.

moisture-retention curve

A graph showing the soil-moisture percentage (by weight or by volume) versus applied tension or pressure. Points on the graph are usually obtained by increasing or decreasing the applied tension or pressure over a specified range.

moisture-volume percentage

The ratio of the volume of water in a soil to the total bulk volume of the soil.

moisture-weight percentage

The moisture content expressed as a percentage of the ovendry weight of soil. See also dry-weight percentage.

monolith (soil)

A vertical section of a soil profile removed from the soil and mounted for display or study.

montmorillonite

A specific aluminous member of the smectite group.

montmorillonite group

Clay minerals having a 2:1 expanding crystal lattice. Isomorphous substitution gives the various types and causes a net permanent charge balanced by cations in such a manner that water may move between the sheets, giving reversible cation exchange and very plastic properties. Synonymous with smectite.

mor (or raw humus)

A nonzoogenous forest humus form distinguished by a matted F layer and a holorganic H layer with a sharp delineation from the A horizon. It is generally acid, having high organic carbon content (52% or more) and a high C:N ratio (25-35, sometimes higher). Various subgroups can be recognized by the morphology, and chemical and biological properties.

moraine

An accumulation of earth, generally with stones, carried and finally deposited by a glacier. Several kinds of moraines are distinguished, such as ground moraine and end moraine.

morphology (soil)

1. The physical constitution, particularly the structural properties, of a soil profile as exhibited by the kinds, thickness, and arrangement of the horizons in the profile, and by the texture, structure, consistence, and porosity of each horizon. 2. The structural characteristics of the soil or any of its parts.

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 markedly and should be specified in the soil description.

mottles

Spots or blotches of different color or shades of color interspersed with the dominant color.

mottling

Formation or presence of mottles in the soil.

muck soil

An organic soil consisting of highly decomposed materials. Mucky peat and peaty muck are terms used to describe increasing stages of decomposition between peat and muck.

mudflow slide

Movement of large masses of ""quick clay.""

mulch

Any material such as straw, sawdust, leaves, plastic film, or loose soil that is spread on the surface of the soil to protect the soil and the plant roots from the effects of raindrops, soil crusting, freezing, and evaporation.

mulch (to)

To apply a mulch to the surface of the soil.

mulch farming

A system of farming in which the organic residues are not plowed into or mixed with the soil but are left on the surface as a mulch.

mull

A zoogenous forest humus form consisting of an intimate mixture of well-humified organic matter and mineral soil that makes a gradual transition to the horizon underneath. It is distinguished by its crumb or granular structure, and because of the activity of the burrowing microfauna (mostly earthworms), partly decomposed organic debris does not accumulate as a distinct layer (F layer) as in mor and moder. The organic matter content is 5-20% and the C:N ratio is 10-15. Various subgroups can be distinguished by the morphology and chemical characteristics. Ah horizon.

Munsell color system

A color designation system specifying the relative degrees of the three simple variables of color: hue, value and chroma. For example: 10YR 6/4 is the color of a soil having a hue of 10YR, value of 6 and chroma of 4. These notations can be translated into several different systems of color names. See also chroma, hue and value, color.

mycelium

A mass of threadlike filaments, branched or composing a network, that constitutes the vegetative structure of a fungus.

mycorrhiza

The association usually symbiotic of fungi with the roots of seed plants. See also ectotrophic mycorrhiza and endotrophic mycorrhiza.