Here is a listing of the most commonly used terms and definitions associated with soils, agriculture, geology, and mineralogy.
 
 

A

Abrasion: The physical weathering of a rock surface by running water, glaciers or wind laden with fine particles. See Ventifact.

Absorption: The physical uptake of water and/or ions by a substance. For example, soils absorb water.

Accelerated Erosion: An increased rate of erosion caused by humans.

Accessory Minerals: Minerals occurring in small quantities in a rock whose presence or absence does not affect the true nature of the rock.

Accumulation: The build-up or increase of one or more constituents in the soil at a given position as a result of translocation. The build-up may be a residue due to the translocation of material out of the horizon or may be due to an addition of material. Usually refers to soluble substances and clay particles.

Acicular: Needle shaped.

Acid Rock: An igneous rock that contains more than 60 per cent silica and free quartz.

Acid Soil: A soil with a pH<6.5.

Acidity: The hydrogen ion activity in the soil solution expressed as a pH value.

Actinomycetes: A group of organisms intermediate between the bacteria and the true fungi, mainly resembling the latter because they usually produced branched mycelium.

Actinomycetes: Family of microorganisms belonging to a group intermediary between bacteria and molds (fungi); a form of filamentous, branching bacteria.

Adsorption Complex: The various substances in the soil that are capable of adsorption, these are mainly clay or humus

Adsorption Complex: The various substances in the soil that are capable of adsorption, these are mainly clay or humus

Adsorption, also adsorb, fixation: The attachment of a particle, ion or molecule to a surface. Calcium is adsorbed onto the surface of clay or humus.

Adsorption: The attachment of a particle, ion or molecule to a surface. Calcium is adsorbed onto the surface of clay or humus.

Aeolian Deposits: Fine sediments transported and deposited by wind; they include loess, dunes, desert sand and some volcanic ash.

Aeolian: Pertaining to wind action.

Aeration: The process by which atmospheric air enters the soil. The rate and amount of aeration depends on the size and continuity of the pore spaces and the degree of water logging.

Aerial Photograph: A photograph of the Earth's surface taken from an airplane or some other type of airborne equipment.

Aerobic Organism: Organisms living or becoming active in the presence of molecular oxygen.

Aerobic: Conditions having a continuous supply of molecular oxygen. compost - composting environment characterized by bacteria active in the presence of oxygen (aerobes); generates more heat and is a faster process than anaerobic composting.

Aerobic temperatures may reach over 140° F - high enough to destroy pathogens, weed seeds, and fly ova; creates no excessive unpleasant odors; the most rapid composting process occurs with enclosed aerobic systems.

AFP: Air filled porosity; the air capacity of a compost.

Aggregates: Discrete clusters of particles formed naturally of artificially and including such particles as crumbs, granules, clods, fecal pellets, fragments of fecal pellets and concretions.

Aggregation: The process by which particles coalesce to form aggregates.

Agricultural Waste: Waste materials produced from the raising of plants and animals, including manures, bedding, plant stalks, hulls, leaves and vegetable matter.

Agronomy: That part of agriculture devoted to the production of crops and soil management - the scientific utilization of agricultural land.

Air Classification: the separation of mixed waste materials using a moving stream of air; light wastes are carried upward while heavy components drop out of the stream.

Algae: Unicellular of multi-cellular plants containing chlorophyll. The are aquatic or occur in damp situations and include most seaweeds.

Alkaline Soil: A soil with pH >7.3

Allelopathy - the suppression of growth of one plant species by another due to the release of toxic substances.

Alluvial Pan or Alluvial Cone: Sediments deposited in a characteristic fan or cone shape by a mountain stream as it flows on to a plain or flat open valley.

Alluvial Plain: A flat area built up of alluvium.

Alluvial Soil: A general term for those soils developed on a fairly recent alluvium.

Alluvium: A sediment deposited by streams and varying widely in particle size. The stones and boulders when present are round or sub-rounded. Some of the most fertile soils are derived from alluvium of medium or fine texture.

Amendment (Soil): A material that is added to soil to improve chemical or physical characteristics or as a means of treating a waste material.

Amino Acid: An organic compound containing both the amino (NH₂) and carboxyl (COOH) groups. Amino acid molecules combine to form proteins, therefor they are a fundamental constituent of living matter. They are synthesized by autotrophic organisms, principally green plants.

Ammonia Fixation: Adsorption of ammonium ions by clay minerals, rendering them insoluble and non-exchangeable.

Ammonification: The production of ammonia by microorganisms through the decomposition of organic matter.

Anaerobic Organism: One that lives in an environment without molecular oxygen.

Anaerobic: Conditions that are free of molecular oxygen. In soils this is usually caused by excessive wetness.

Compost: composting environment characterized by bacteria active in the absence of oxygen (anaerobes). In anaerobic composting, the microflora obtain oxygen from the waste; peak temperatures may reach 100 to 130° F; digestion requires more time, foul odors are created and pathogens may survive.

Anion Exchange Capacity: The total amount of anions that a soil can adsorb, usually expressed as mmol_c per kg soil.

Anion: An ion having a negative charge.

Anisotropic: 1. General: possessing different physical properties in different directions 2. General: having physical properties that depend on direction 3. Minerals or parts of soils: alternately bright and dark between crossed polars when the microscope stage is rotated. The bright position is due to the formation of interference colors. SEE INTERFERENCE COLORS.

Annelid: Red blooded worm such as an earthworm.

Annual Plant: A plant that completes its life cycle within one year.

Arid: A term applied to a region or climate in which precipitation is too low to support crop production.

Arthropod: A member of the phylum arthropoda which is the largest in the animal kingdom. It includes insects, spiders, centipedes, crabs, etc.

Aspect: The compass direction of a slope.

Aureole: Halo or ring around a feature.

Autotrophic Organism: Organisms that utilize carbon dioxide as a source of carbon and obtain their energy from the sun or by oxidizing inorganic substances such as sulfur, hydrogen, ammonium, and nitrate salts. The former include the higher plants and algae and the latter various bacteria, cf. HETEROTROPHIC

Available Elements: The elements in the soil solution that can readily be taken up by plant roots.

Available Nutrients: SEE AVAILABLE ELEMENTS

Available Water Capacity: The weight percentage of water which a soil can store in a form available to plants. It is equal to the moisture content at field capacity minus that at the wilting point.

Available Water: That part of the water in the soil that can be taken up by plant roots.
 
 

B

B.S.: An abbreviation for Base Saturation.

Bacteria: Unicellular or multicellular microscopic organisms. They occur everywhere and in very large numbers in favorable habitats such as soil and sour milk where they number many millions per gram.

Bar: 10 to the power of 5 Pascal or 10 to the power of 5(Nm to the power of -2).

Basalt: A fine grained igneous rock forming lava flows or minor intrusions. It is composed of plagioclase, augite and magnetite; olivine may be present.

Base saturation: The extent to which the exchange sites of a material are occupied by exchangeable basic cations; expressed as % of the cation exchange capacity.

Basic Rock: An igneous rock that contains less than 55% silica.

Bedrock: The solid rock at the surface of the earth or at some depth beneath the soil and superficial deposits.

Biennial: A plant that completes its life cycle in two years.

Bioassay - a laboratory assay (test) using a biological test organism.

Bioavailable - available for biological uptake

Biodegradability - the potential of an organic component for conversion into simpler structures by enzymatic activity.

Biological Oxygen Demand (BOD) - the amount of oxygen used in the biochemical oxidation of organic matter; an indication of compost maturity and a tool for studying the composting process.

Biomass: a) the weight of a given organism in a volume of soil that is one m squared at the surface and extending down to the lower limit of the organism's penetration. b) The weight of organisms in a given area or volume.

Biosolids: Primarily organic solid product produced by the wastewater treatment process that can be beneficially recycled.

Birefringence: The numerical difference in value between the highest and lowest refractive index of a mineral. This is not synonymous with interference colors. SEE INTERFERENCE COLORS.

Blocky: Many sided with angular or rounded corners, used for describing peds.

Bog Iron Ore: A ferruginous deposit in bogs and swamps formed by oxidizing algae, bacteria or the atmosphere on iron in solution.

Boulder Clay: SEE TILL.

Buffer: A substance that prevents a rapid change in pH when acids or alkalis are added to the soil, these include clay, humus and carbonates.

Bulk Density: Mass per unit volume of undisturbed soil, dried to constant weight at 105°C (221°F). Usually expressed as g/cc.

Bulking Agent: Material, usually carbonaceous such as sawdust or woodchips, added to a compost system to maintain airflow by preventing settlement and compaction of the waste.
 
 

C

Cadmium to Zinc Ratio (Cd:Zn Ratio) - ratio of the elements used to study heavy metal accumulation by animals.

Calcareous Soil: A soil that contains enough calcium carbonate so that it effervesces when treated with hydrochloric acid.

Calcification: Used by some to refer to the processes of calcium carbonate accumulation.

Calcite: Crystalline calcium carbonate, CaCO3. Crystallizes in the hexagonal system, the main types of crystals in soils being dog-tooth, prismatic, nodular, fibrous, granular, and compact.

Caliche: A layer or horizon cemented by the deposition of calcium carbonate. It usually occurs within the soil but may be at the surface due to erosion.

Capillarity: The process by which moisture moves in any direction through the fine pore spaces and as films around particles.

Capillary Fringe: The zone just above the water-table that remains practically saturated with water.

Capillary Moisture: That amount of water that is capable of movement after the soil has drained. It is held by adhesion and surface tension as films around particles and in the finer pore spaces.

Carbohydrates - various kinds of sugars, generally easily assimilated by bacteria.

Carbon to Nitrogen Ratio (C:N Ratio) - ratio representing the quantity of carbon (C) in relation to the quantity of nitrogen (N) in a soil or organic material; determines the composting potential of a material and serves to indicate product quality.

Catena: A sequence of soils developed from similar parent material under similar climatic conditions but whose characteristics differ because of variations in relief and drainage.

Cation Exchange Capacity (CEC): The total potential of soils for adsorbing cations, expressed in millimoles of charge per kg (mmolc/kg) of soil. Determined values depend somewhat on the method employed. compost: a routine measure of the binding potential of a soil; measures the soil's ability to remove negative ions from metals and other compounds, allowing the ions to form insoluble compounds and precipitate in the soil; determined by the amount of organic matter and the proportion of clay to sand; the higher the CEC, the greater the soil's ability to bind metals.

Cation Exchange: The exchange between cations in solution and cations held on the exchange sites of minerals and organic matter.

Cation. An ion having a positive electrical charge.

CEC: An abbreviation of Cation Exchange Capacity.

Cellulose - carbon component of plants, not easily digested by microorganisms.

Cemented: Massive and either hard or brittle depending on the content of cementing substances such as calcium carbonate, silica, oxides of iron and aluminum, or humus.

Chalk: The term refers to either (a) soft white limestone which consists of very pure calcium carbonate and leaves little residue when treated with hydrochloric acid, and sometimes consists largely of the remains of foraminifera, echinoderms, mollusks, and other marine organisms, or (b) The upper or final member of the cretaceous system.

Chamber: A relatively large circular or ovoid pore with smooth walls and an outlet through channels or planar pores.

Channel: A tubular-shaped pore.

Chemical Oxygen Demand - a measure of the oxygen equivalent of that portion of organic matter in a sample that is susceptible to oxidation by a strong chemical oxidant; an important, rapidly measured parameter for stream and industrial waste studies and for control of waste treatment plants.

Chlorosis: The formation of pale green or yellow leaves in plants resulting in the failure of chlorophyll to develop. It is often caused by a deficiency in an essential element.

Chroma: The relative purity of a color directly related to the dominance of the determining wavelength. One of the three variables of color.

Chronosequence: A sequence of soils that changes gradually from one to the other with time.

Clay Coating; SEE COATING.

Clay Mineral: Crystalline or amorphous mineral material,<2mm in diameter.

Clay Pan: A middle or lower horizon containing significantly more clay than the horizon above. It is usually very dense and has a sharp upper boundary. Clay pans generally impede drainage, are usually plastic and sticky when wet and hard when dry.

Clay: Either 1. Mineral material <2mm. 2. A class of texture. 3. Silicate clay materials.

Cleavage: The ability of a mineral or rock to split along predetermined planes.

Climax Vegetation: A fully developed plant community that is in equilibrium with its environment.

Clod: A mass of soil produced by disturbance.

Coating: A layer of a substance completely or partly covering a surface. Coatings are composed of a variety of substances separately or in combination. They include clay coatings (clay skins), calcite coatings, whole soil coatings, etc. Coatings may become incorporated into the matrix or be fragmented

Coefficient of Linear Extensibility: The ratio of the difference between the moist and dry lengths of a clod to its dry length, (Lm-Ld)/Ld when Lm is the moist length at (1/3 atmospheres) and Ld is the air-dry length. The measure correlates with the volume change of a soil upon wetting and drying.

COLE: An abbreviation of coefficient of linear extensibility.

COD: see CHEMICAL OXYGEN DEMAND.

Colloid: The organic and inorganic material with very fine particle size and therefor high surface area which usually exhibits exchange properties.

Colluvium: Soil materials with or without rock fragments that accumulate at the base of steep slopes by gravitational action.

Compaction: Increase in bulk density due to mechanical forces such as tractor wheels.

Composite Structure: Any combination of different types of pedounits.

Compost: Plant and animal residues that are arranged into piles and allowed to decompose, sometimes soil or mineral fertilizers may be added. The stabilized product of composting which is beneficial to plant growth; it has undergone an initial, rapid stage of decomposition and is in the process of humification.

Compost: Plant and animal residues that are arranged into piles and allowed to decompose, sometimes soil or mineral fertilizers may be added. The stabilized product of composting which is beneficial to plant growth; it has undergone an initial, rapid stage of decomposition and is in the process of humification.

Composting - the biodegradation, usually aerobic and thermophilic, that: involves a heterogeneous organic substrate in the solid state; evolves by passing through a thermophilic stage with a temporary release of phytotoxins; results in the production of carbon dioxide, water, minerals and stabilized organic matter.

Composting, Municipal - solid waste management method whereby the organic component of the solid waste stream is biologically decomposed under controlled conditions; an aerobic process in which waste organic materials are ground or shredded and then decomposed to humus in windrow piles or in mechanical digesters, drums, or similar enclosures; results in volume and odor reduction, waste stabilization, destruction of pathogens, larvae and weed seeds; the final product is sufficiently stable for storage and land application without adverse environmental effects.

Compound Structure: Large peds such as prisms and columns that are themselves composed of smaller incomplete peds.

Concretion: Small, hard local concentrations of material such as calcite, gypsum, iron oxide, or aluminum oxide. Usually spherical or subspherical but may be irregular in shape.

Condensate - moisture in the air that is pulled through a compost pile.

Conductivity - a measure of the soluble salts in the soil; used as an overall indicator of the level of macro- and micronutrients in the soil.

Conglomerate: A sedimentary rock composed mainly of rounded boulders.

Coniferous Forest: A forest consisting of predominantly cone-bearing trees with needle shaped leaves: usually evergreen but some are deciduous, for example the larch forests(Larix dehurica) of central Siberia. Their greatest extent is in the wide belt across northern Canada and northern Eurasia. Coniferous forests produce soft wood which has a large number of industrial applications including paper making.

Consistence: The resistance of the soil to deformation or rupture as determined by the degree of cohesion or adhesion of the soil particles to each other.

Consolidated: A term that usually refers to compacted or cemented rocks.

Contaminant - foreign material lending impurity to a primary material; physical contaminants of compost include glass and plastic, chemical contaminants include heavy metals and toxic organic compounds.

Continuously Anaerobic (very poorly drained): A horizon that is saturated with water throughout the year, it is blue, olive or gray.

Creep: Slow movement of masses of soil down slopes that are usually steep. The process takes place in response to gravity facilitated by saturation with water.

Crotovina: An animal burrow which has been filled with material from another horizon.

Croute Calcaire: A synonym for caliche.

Crust: A surface layer of soils that becomes harder than the underlying horizon.

Curing - late stage of composting, after much of the readily metabolized material has been decomposed, which provides additional stabilization and allows further decomposition of cellulose and lignin.

Cutans: Coatings or deposits of material on the surface of peds, stones, etc.A common type is the clay cutan caused by translocation and deposition of clay particles on ped surfaces.
 
 

D

Deciduous Forest: A forest composed of trees that shed their leaves at some season of the year. In tropical areas the trees lose their leaves during the hot season in order to conserve moisture. Deciduous trees of the cool areas shed their leaves during the autumn to protect themselves against the cold and frost of winter. Deciduous forests produce valuable hardwood timber such as teak and mahogany from the tropics, oak and beech come from the cooler areas.

Decomposition - conversion of organic matter as a result of microbial and/or enzymatic interactions; initial stage in the degradation of an organic substrate, characterized by processes of destabilization of the pre-existing structure.

Deficiency symptom. A result, including slow plant growth, chlorosis or necrosis, caused by the lack of a plant essential element.

Deficiency. The lack of an adequate amount of a plant nutrient.

Deflation: Preferential removal of fine soil particles from the surface soil by wind. SEE DESERT PAVEMENT.

Deflocculate: To separate of disperse particles of clay dimensions from a flocculated condition.

Delta: A roughly triangular area of the mouth of a river composed of river transported sediment.

Denitrification: The biological reduction of nitrogen to ammonia, molecular nitrogen or oxides of nitrogen, resulting in the loss of nitrogen into the atmosphere and therefor undesirable in agriculture.

Denudation: Sculpturing of the surface of the land by weathering and erosion; leveling mountains and hills to flat or gently undulating plains.

Deposit: Material placed in a new position by the activity of humans or natural processes such as wind, water ice or gravity.

Desert Crust: A hard surface layer in desert regions containing calcium carbonate, gypsum, or other cementing materials.

Desert Pavement: A layer of gravel or stones remaining on the surface of the ground in deserts after the removal of fine material by wind. SEE DEFLATION AND HAMADA.

Desert Varnish: A glossy sheen or coating on gravel or stones in arid regions.

Devonian: A period of geological time extending from 320-280 million years BP.

Diatoms: Algae that possess a siliceous cell wall which remains preserved after the death of the organisms. They are abundant in both fresh and salt water and in a variety of soils.

Dispersion: The process whereby the structure or aggregation of the soil is destroyed so that each particle is separate and behaves as a unit.

Doline or Dolina: A closed depression in a karst region often rounded or elliptical in shape, forms by the solution and subsidence of the limestone near the surface. Sometimes at the bottom is a sink hole into which surface water flows and disappears underground.

Domain: A bundle of clay particles that is only visible in crossed polarized light.

Drift: A generic term for superficial deposits including till (boulderclay), outwash gravel and sand, alluvium, solifluction deposits and loess.

Drum Composting System - enclosed cylindrical vessel which slowly rotates for a set period of time to break up and decompose material.

Drumlin: A small hill, composed of glacial drift with hog back outline, oval plan, and long atlas oriented in the direction of ice movement. Drumlins usually occur in groups, forming what is known as basket of eggs topography.

Dry-Farming: A method of farming in arid and semi-arid areas without using irrigation, the land being treated so as to conserve moisture. The technique consists of cultivating a given area in alternate years allowing moisture to be stored in the fallow year. Moisture losses are reduced by producing a mulch and removing weeds. In Siberia, where melting snow provides much of the moisture for spring crops, the soil is ploughed in the autumn providing furrows in which snow can collect, preventing it from being blown away and evaporated by strong winds. Usually alternate narrow strips are cultivated in an attempt to reduce erosion in the fallow year. Dry farming methods are employed in the drier regions of India, USSR, Canada and Austria.

Dunes, Sand Dunes: Ridges or small hills of sand which have been piled up by wind action on sea coasts, in deserts, and elsewhere. Barkhans are isolated dunes with characteristic crescentic forms.

Dynamic Pile System - compost piles receive forced aeration and are not turned. See Also: aerated static pile.
 
 

E

Ecology: The study of interrelationships between individual organisms, and between organisms and their environments.

Ecosystem: A group of organisms interacting among themselves and with their environment.

Edaphic: (1) Of or pertaining to the soil. (2) Influenced by soil factors.

Edaphology: The study of the relationships between soil and soil including the use of the land by humans.

Efflorescence: The accumulation of dissolved substance (usually simple salts) at a surface due to evaporation.

Eluvial Horizon: A horizon from which material has been removed either in solution or suspension.

Eluviation: Removal of material from the upper horizon in solution or suspension.

Enclosed System - See: In-Vessel.

Equatorial Forest or Tropical Rain Forest: A dense, luxuriant, evergreen forest of hot, wet equatorial regions containing many trees of tremendous heights, largely covered with lianas and epiphytes. Individual species of trees are infrequent but they include such valuable tropical hardwoods such as mahogany, ebony and rubber. Typical equatorial forests occur in Zaire and Amazon basins in southeastern Asia.

Erosion Pavement: A layer of gravel or stones left on the surface of the ground after the removal of the fine particles by erosion.

Erosion: The removal of material from the surface of the land by weathering, running water, moving ice, wind and mass movement.

Esker: A long narrow ridge, chiefly of gravel and sand formed by a melting glacier or ice sheet.

Essential element. The elements C, H, O, P, K, N, S, Ca, Mg, K, B, Mn, Cu, Zn, Mo, Cl, Co, Si and F. These must be taken up and utilized in sufficient quantities for plants to complete their life cycles.

Eutrophic: Containing an optimum concentration of plant nutrients.

Evapotranspiration: The combined processes of evaporation and transpiration.

Excessively Aerobic: A horizon which is usually too dry to support adequate plant growth.

Excessively Drained: A soil that loses water very rapidly because of rapid percolation.

Exchangeable Cation: A cation such as calcium that is adsorbed onto a surface, usually clay or humus and is capable of being easily replaced by another cation such as potassium. Exchangeable cations are readily available to plants.

Exfoliation: A weathering process during which thin layers of rock peel off from the surface. This is caused by the heating of the rock surface during the day and cooling at night leading to alternate expansion and contraction. This process is sometimes termed "onion skin weathering".
 
 

F

Fabric: SEE SOIL FABRIC.

Facultative Aerobic Organisms - organisms capable of growing under both aerobic and anaerobic conditions

Fecal Material: The various types of feces or excrement produced by soil fauna.

Fallow: Leaving the land uncropped for a period of time. This may be to accumulate moisture, improve structure or induce mineralization of a nutrient.

Family: One of the categories in soil classification intermediate between the great soil group and the soil series.

Fen Peat: Peat that is neutral to alkaline due to the presence of calcium carbonate.

Fertilizer: A material that is added to the soil to supply one or more plant nutrients in a readily available form.

Field Capacity or Field Moisture Capacity: The total amount of water remaining in a freely drained soil after the excess has flowed into the underlying unsaturated soil. It is expressed as a percentage of the oven-dry soil.

Fine Material: Soil material in thin sections composed of particles less than 2mm which are difficult or impossible to resolve with the petrological microscope.

Fine Texture: Containing >35 per cent clay.

Finishing - post-processing; screening, grinding, or a combination of similar processes to remove plastics, glass, and metals remaining after composting.

Flood Plain: The land adjacent to a stream, built of alluvium and subject to repeated flooding.

Fluvent: Floodplain soils, characterized by buried horizons and irregularly decreasing amounts of organic matter with depth.

Fluvio-Glacial: SEE GLACIAL-FLUVIAL DEPOSITS.

Folist gleization: A process in saturated or nearly saturated soils which involves the reduction of iron, its segregation into mottles and concretions, or its removal by leaching from the gleyed horizon.

Fractionation: In this study, using different chemicals to remove chemically different forms of phosphorus.

Fragipan: Brittle subsurface restricting soil horizon, usually loamy textured and weakly cemented.

Fragment: A small mass of soil produced by a disturbance.

Freely Drained: A soil that allows water to percolate freely.

Friable: A term applied to soils that when either wet or dry crumble easily between the fingers.

Fulvic Acid: The mixture of organic substances remaining in solution upon acidification of a dilute alkali extract of soil.

Fungi: Simple plants that lack chlorophyll and are composed of cellular filamentous growth known as hyphae. Many fungi, but their fruiting bodies, viz. mushrooms and puffballs are quite large. in composting: saprophytic or parasitic multinucleate organisms with branching filaments called hyphae, forming a mass called a mycelium; fungi bring about cellulolysis and humification of the substrate during stabilization.
 
 

G

Gastropod: A member of the Gastropoda class of molluscs which includes snails and slugs.

Geomorphology: The study of the origin of physical features of the Earth, as they are related to geological structure and denudation.

Gilgai: A distinctive microrelief of knolls and basins that develop on clay soils that exhibit a considerable amount of expansion and contraction in response to wetting and drying.

Glacial Drift: Materials transported by glaciers and deposited directly from the ice of from the meltwater.

Glacier: A large mass of ice that moves slowly over the surface of the ground or down a valley. They originate in snowfields and terminate at lower elevations in a warmer environment where they melt.

Glacio-Fluvial Deposits: Material deposited by meltwaters coming from a glacier. These deposits are variously stratified and may form outwash plains, deltas, kames, eskers, and kame terraces. SEE GLACIAL DRIFT AND TILL.

Gleization: SEE GLEYING.

Gleyed: A soil condition resulting from gleization which is manifested by the presence of neutral gray, bluish or greenish colors through the soil matrix or in mottles (spots or streaks) among other colors.

Gleying: The reduction of iron in an anaerobic environment leading to the formation of gray or blue colors.

Granite: An igneous rock that contains quartz, feldspar and varying amounts of biotite and muscovite.

Gravitational Water: The water that flows freely through soils in response to gravity.

Great Soil Group: One of the Categories in soil classification.

Groundwater-Table: The upper limit of the groundwater.

Growing season: The portion of the year when soil temperatures are above biologic zero 41°F (4°C).

Gully Erosion: A form of catastrophic erosion that forms gullies.

Gully: A shallow steep-sided valley that may occur naturally or be formed by accelerated erosion.

Gyttja: Peat consisting of fecal material, strongly decomposed plant remains, shells of diatoms, phytoliths, and fine material particles. Usually forms in standing water.
 
 

H

Halomorphic Soil: A soil containing a significant proportion of soluble salts.

Halophyte: A plant capable of growing in salty soil; i.e. a salt tolerant plant.

Halophytic Vegetation: Vegetation that tolerates or requires saline conditions.

Hamada: An accumulation of stones at the surface of deserts, formed by the washing or blowing away of the finer material.

Hardpan: A horizon cemented with organic matter, silica, sesquioxides, or calcium carbonate. Hardness or rigidity is maintained when wet or dry and samples do not slake in water.

Heavy Metals: Trace elements regulated because of their potential for human, plant, or animal toxicity, including cadmium (Cd), copper (Cu), chromium (Cr), mercury (Hg), nickel (Ni), lead (Pb) and Zinc (Zn).

Heavy Soil (Obsolete): A soil that has a high content of clay and is difficult to cultivate.

Heterogeneous: Complex and not easily described.

Heterotrophic Organisms: Those that derive their energy by decomposing organic compounds, cf. AUTOTROPHIC.

High water mark: A distinct mark made on vegetation, buildings or rocks that shows the extent of water rise.

Histosol: A soil "order" in the taxonomic system that is composed of mucks and peats that have a high concentration of organic materials in the surface soil or overly rock.

Holocene Period: The period extending from 10,000-0 years BP.

Horizon: Relatively uniform materials that extend laterally, continuously or discontinuously throughout the pedounit; runs approximately parallel to the surface of the ground and differs from the related horizons in many chemical, physical and biological properties.

Hue: The dominant spectral color and one of the three color variables.

Humic Acid: Usually refers to the mixture of ill-defined dark organic substances precipitated upon acidification of a dilute alkali extract of soil. Some workers use it to include only the alcohol-insoluble portion of the precipitate. The main constituent of humus, composed of proteins and lignins, dark brown to black in color.

Humification: The decomposition of organic matter leading to the formation of humus. The microbial synthesis of three-dimensional polymers of saccharides and phenols resembling gums and lignin; a process of storing organic energy in compounds of high molecular weight which are slowly degradable (10-100+ years).

Humin: Usually applied to that part of the organic matter that remains after extraction with dilute alkali.

Humus: The well-decomposed, relatively stable part of the organic matter found in aerobic soils. A complex aggregate of amorphous substances, formed during the microbial decomposition or alteration of plant and animal residues and products synthesized by soil organisms; principal constituents are derivatives of lignins, proteins and cellulose; humus has a high capacity for base exchange (CEC), combining with inorganic soil constituents, and for water absorption; finished compost may be designated by the general term humus.

Hydration: The process whereby a substance takes up water.

Hydraulic Conductivity: The rate at which water will move through soil in response to a given potential gradient.

Hydric soil. A soil that is saturated with water long enough during the plant growing season to become anaerobic. This soil will usually be characterized by anaerobic soil zones and wetland vegetation.

Hydrologic Cycle: Disposal of precipitation from the time it reaches the soil surface until it re-enters the atmosphere by evapotranspiration to serve again as a source of precipitation.

Hydrolysis: In soils it is the process whereby hydrogen ions are exchanged for cations such as sodium, potassium, calcium and magnesium.

Hydromorphic Soil: Soils developed in the presence of excess water.

Hydrophytic vegetation. Plants that can exist in water that at least periodically is subject to anaerobic conditions.

Hygroscopic Water: Water that is adsorbed onto a surface from the atmosphere.
 
 

I

Igneous Rock: A rock formed by cooling of molten magma including basalt and granite.

Illuvial Horizon: A horizon that receives material in solution or suspension from some other part of the soil.

Illuviation: The process of movement of material from one horizon and its deposition in another horizon of the same soil; usually from an upper horizon to a middle or lower horizon in the pedounit. Movement can also take place laterally.

Immature Soil: Lacking a well developed pedounit.

Immobilization - conversion of an element from its inorganic form to its organic form within microbial or plant tissues, rendering it unavailable to other organisms or plants

Impeded Drainage: Restriction of the downward movement of water by gravity.

Imperfectly drained: A soil that shows a small amount of reduction of iron due to short periods of water-logging.

Impervious: Not easily penetrated by roots or water.

Incubation Study - study done in a laboratory setting under controlled temperature and moisture conditions.

Inerts - non-biodegradable products contained in wastes (glass, plastics, etc.)

Infiltration: The process whereby water enters the soil through the surface.

Inorganic - substance in which carbon-to-carbon bonds are absent; mineral matter.

Inselberg: (pl. inselberge) A steep sided hill composed predominantly of hard rock and rising abruptly above a plain; found mainly in tropical and subtropical areas.

Insoluble: Not capable of being dissolved. For instance, insoluble phosphorus is present in the solid phase in soils.

Interglacial Period: A relatively mild period occuring between two glacial periods.

Intergrade: A soil which contains the properties of two distinctive and genetically different soils.

Interstadial Period: A slightly warmer phase during a glacial period.

Intrazonal Soils: One of the three orders of the zonal system of soil classification. They have well developed characteristics resulting from the dominant influence of a local factor such as topography and parent material.

Isomorphous Replacement: The replacement of one ion by another in the crystal lattice without changing the structure of the mineral.
 
 

J
 
 

K

Karst Topography: An irregular land surface in a limestone region. The principal features are depression (e.g. dolines which sometimes contain thick soils which have been washed off the rest of the surfaces leaving them bare and rocky.) Drainage is usually by underground streams.

Krotovina: SEE CROTOVINA.
 
 

L

Labile: Term applied to denote element that can be solubilized in a relatively short period of time. For instance, a labile nutrient is not directly available, but will be release relatively quickly.

Lacustrine Deposit: Materials deposited by lake waters.

Lacustrine: Pertaining to lakes.

Land Reclamation - the restoration of productivity to lands made barren through processes such as erosion, mining or land clearing.

Landslide or Landslip: The movement down the slope of a large mass of soil or rocks from a mountain or cliff. Often occurs after a torrential rain which soaks into the soil making it heavier and more mobile. Earthquakes and the undermining action of the sea are also causative agents.

Lattice Structure: The orderly arrangement of atoms in crystalline material.

Leaching: The washing out of material from the soil, both in solution and suspension.

Leaching: The process by which nutrient chemicals or contaminants are dissolved and carried away by water, or are moved into a lower layer of soil.

Light Soil: (obsolete) A soil which has a course texture and is easily cultivated.

Lignin - the component of wood responsible for its rigidity.

Lime: Compounds of calcium used to correct the acidity of soils.

Lipids - a generic term for all fats, oils and related fatty compounds.

Litter: The freshly fallen plant material occurring on the surface of the ground.

Loading Rate - measure of application amount, based on nutrients, trace metals or total mass of material.

Lodging: The collapse of top heavy plants, particularly grain crops because of excess growth or beating by rain.

Loess: An aeolian deposit composed mainly of silt which originated in arid regions, from glacial outwash or from alluvium. It is usually of yellowish brown color and has a widely varying calcium carbonate content. In the USSR, loess is regarded as having been deposited by water.

Lysimeter: Apparatus installed in the soil for measuring percolation and leaching.
 
 

M

Macroelement: Elements such as nitrogen that are needed in large amounts for plant growth. Nutritive elements needed in large quantities to ensure normal plant development (N,P,K, S, Mg, Ca, Fe).

Macronutrient: SEE MACROELEMENT.

Macropores: Pores >100 mm in diameter.

Mangrove Swamp: A dense jungle of mangrove trees which have the special adaptation of extending from their branches long arching roots which act as anchors and form an almost impenetrable tangle. They occur in tropical and subtropical areas, particularly near the mouths of rivers.

Manure: Animal excreta with or without a mixture of bedding or litter.

Matrix: The fine Material ( generally <2mm) forming a continuous phase and enclosing coarser material and/or pores.

Mature Soil: A well developed soil usually with clearly defined horizonation.

Meristem: The region of active cell-division in plants. The cells so formed then become modified to form the various tissues such as the epidermis and cortex.

Mesofauna: Small organisms such as worms and insects.

Metabolism - sum of the chemical reactions within a cell or whole organism, including the energy-releasing breakdown of molecules (catabolism), and the synthesis of complex molecules and new protoplasm (anabolism).

Metamorphic Rock: A rock that has been derived from other rocks by heat and pressure. The original rock may have been igneous, sedimentary, or another metamorphic rock.

Microbe, Soil. A soil microorganism.

Microbial. Pertaining to microbes.

Microclimate: The climate of a very small region.

Microelement: Those elements that are essential for plant growth but are required only in very small amounts. Nutritive elements needed in small quantities for healthy plant development; trace elements (Mn, B, Cl, Zn, Cu, Mo).

Microfauna: The small animals that can only be seen with a microscope; they include protozoa, nematodes, etc.

Microflora: The small plants that can only be seen with a microscope; they include algae, fungi, bacteria, etc.

Micronutrient: SEE MICROELEMENT.

Microorganisms: The members of the microflora and microfauna that can only be seen with a microscope.

Micropores: Pores 5-30mm in diameter.

Microrelief: Small differences in relief that have differences in elevation up to about 2 m.

Mineral Soil: A soil that is composed predominantly of mineral material cf. ORGANIC SOIL.

Mineral-N: Nitrogen in its inorganic form, usually as nitrates or ammonium.

Mineralization: The change of an element in an organic form to an inorganic form by microorganisms.

Mites: Very small members of the arachnid which includes spiders; they occur in large numbers in many organic surface soils.

Moder: A kind of decomposition and humus formation which reproduces advanced but incomplete humification of the remains of organism due to good aeration.

Moisture Content - the mass of water lost per unit dry mass when the material is dried at 103°C (217°F) for eight hours or more. The minimum moisture content required for biological activity is 12-15%; it generally becomes a limiting factor below 45 or 50%; expressed as a percentage, moisture content is water weight/wet weight.

Mor: An accumulation of acid organic matter at the soil surface beneath forest.

Moraine: Any type of constructional topographic form consisting of till and resulting from glacial deposition.

Mottles. see Mottling.

Mottling: Patches or spots of different colors usually used for the color pattern developed due to partial anaerobism.

Muck. Highly decomposed organic wet soil.

Muckiness, classification. Highly decomposed organic wet soil.

Mulch: A loose surface horizon that forms naturally or may be produced by cultivation and consists of either inorganic or organic materials. Any suitable protective layer of organic or inorganic material applied or left on or near the soil surface as a temporary aid in stabilizing the surface and improving soil microclimatic conditions for establishing vegetation; mulch reduces erosion and water loss from the soil and can be used to control weeds.

Mulching - the application of a layer of compost to the surface of the soil, creating an interface that accepts water readily yet resists moisture loss through evapotranspiration.

Mull: A crumbly intimate mixture of organic and mineral material formed mainly by worms, particularly by earthworms.

Mycorrhiza - soil-borne fungi that invade the roots of vascular plants and establish a symbiotic relationship; mycorrhiza hyphae, filaments that extend from plant roots, increase the surface area for nutrient and water absorption.
 
 

N

Necessary nutrient. The elements C, H, O, P, K, N, S, Ca, Mg, K, B, Mn, Cu, Zn, Mo, Cl, Co, Si and F. These must be taken up and utilized in sufficient quantities for plants to complete their life cycles. See essential element.

Necrosis. The appearance of dead parts of plants due to a lack of plant growth factors or the presence of toxics or disease. Necrosis can also be confused with the normal senescence of plant parts.

Nematodes - elongated, cylindrical, unsegmented worms; includes a number of plant parasites (a cause of root damage) and human parasites.

Neutral Soil: A soil with pH values 6.5-7.3.

Nitrification: The oxidation of ammonia to nitrite and nitrite to nitrate by microorganisms.

Nitrogen Fixation: The transformation of elemental nitrogen to an organic form by microorganisms.

Non-Silicate: Rock forming minerals that do not contain silicon.

Non-hydric soil. A soil that developed predominantly under oxygenated (aerobic) conditions.

Nutrient deficiency. The lack of an adequate amount of a plant nutrient. Nutrient deficiency may result in a number of symptoms, including poor plant growth, chlorosis or necrosis. Nutrient deficiency symptoms can easily be confused with toxicity symptoms.

Nutrient. The elements C, H, O, P, K, N, S, Ca, Mg, K, B, Mn, Cu, Zn, Mo, Cl, Co, Si and F which are required for plant growth.
 
 

O

Obligate Aerobic Organisms - can only grow in the presence of oxygen.

Obligate Anaerobic Organisms - can only grow in the absence of oxygen.

Onion Skin Weathering: SEE EXFOLIATION.

Order. see SOIL ORDER.

Organic - substance which includes carbon-to-carbon bonds.

Organic Contaminants - synthetic trace organics include pesticides and polychlorinated biphenyls (PCB's).

Organic Matter: portion of the soil that includes microflora and microfauna (living and dead) and residual decomposition products of plant and animal tissue; any carbon assembly (exclusive of carbonates), large or small, dead or alive, inside soil space; generally consists primarily of humus.

Organic Soil: A soil that is composed predominantly of organic matter, usually refers to peat. See HISTOSOL.

Organic-N - nitrogen in organic material.

Outwash: Glacially deposited soil parent material worked and graded by water action from the melting glacial ice.

Oxidation - energy-releasing process involving removal of electrons from a substance; in biological systems, generally by the removal of hydrogen (or sometimes by the addition of oxygen); chemical and/or biochemical process combining carbon and oxygen and forming carbon dioxide (CO2). see REDUCTION.

Oxygen Demand - See: BOD and COD.
 
 

P

Pans: Soil horizons that are strongly compacted, cemented or have a high content of clay.

Parent Material: The original state of the soil. The relatively unaltered lower material in soils is often similar to the material in which the horizons above have formed.

Particle Density: The weight per unit volume of soil solids only.

Pathogen - an organism, chiefly a microorganism, including viruses, bacteria, fungi, and all forms of animal parasites and protozoa, capable of producing an infection or disease in a susceptible host.

Peat: An accumulation of dead plant material often forming a layer many meters deep. It is only slightly decomposed due to being completely waterlogged.

Ped: A single individual naturally occuring soil aggregate such as a granule or prism cf. CLOD OR FRAGMENT.

Pedogenesis: The natural process of soil formation.

Pedology: The study of soils as naturally occurring phenomena taking into account their composition, distribution, and method of formation.

Pedounit: A selected column of soil containing sufficient material in each horizon for adequate laboratory characterization. Also referred to as PEDS.

Pedoturbation: All mixing of soil components that is not caused by illuviation.

Peneplain: A large flat or gently undulation area. Its formation is attributed to progressive erosion by rivers and rain, which continues until almost all the elevated portions of the land surface are worn down. When a peneplain is elevated, it may become a plateau which then forms the initial stages in the development of a second peneplain.

Peraquic. A condition that results from a high soil water table.

Perched Water-Table: The upper limit of perched water.

Percolation: (soil water) The downward or lateral movement of water through soil.

Percolation: (soil water) The downward or lateral movement of water through soil.

Perennial: A plant that continues to grow from year to year.

Permafrost: Permanently frozen subsoil.

Permanent Wilting Point: SEE WILTING POINT.

Permanently flooded. A condition where standing water covers the soil surface throughout normally wet years.

Permeability: The ease with which air, or plant roots penetrate into or pass through a specific horizon.

Persistence - refers to a slowly decomposing substance which remains active in the natural cycle for a long period of time.

pH, Soil: The negative logarithm of the hydrogen ion concentration of a soil solution. The degree of acidity or alkalinity of a soil expressed in terms of the pH scale, from 2 to 10.

pH: The negative logarithm of the hydrogen ion concentration of a solution. It is the quantitative expression of the acidity and alkalinity of a solution and has a scale that ranges from about 0 to 14. pH 7 is neutral, <7 is acid and >7 is alkaline.

Physical Weathering: The communition of rocks into smaller fragments by physical forces such as frost action or exfoliation.

Physiological Drought: A temporary daytime state of drought in plants due to the losses of water by transpiration being more rapid than uptake by roots although the soil may have an adequate supply. Such plants usually recover during the night.

Phytolith: Opaline formation in plant tissue that remains in the soil after the softer plant tissue has decomposed.

Phytotoxic - detrimental to plant growth; caused by the presence of a contaminant.

Phytotoxin - substance causing growth reduction or death in plants.

Plagioclimax: A plant community which is maintained by continuous human activity of a specific nature, such as burning or grazing.

Plastic: A moist or wet soil that can be molded without rupture.

Platy: Soil aggregates that are horizontally elongated.

Pleistocene Period: The period following the Pliocene period, extending from 2,000,0000-10,000 years BP. In Europe and North America, there is evidence of four or five periods of intense cold during this period, when large areas of the land surface were covered by ice - glacial periods. During the interglacial periods, the climate ameliorated and the glaciers retreated.

Pleochroism: (minerals). The changes in color when some transparent minerals are rotated in plane polarized light. It is expressed in terms of the nature and intensity of the color change.

Pluvial Period: A period of hundreds of thousands of years of heavy rainfall.

Polder: A term used in Holland for an area reclaimed from the sea or lake. A dyke is constructed around the area which is then drained by pumping the water out. Polders form valuable agricultural land or pasture land for cattle.

Polygenic Soil: A soil that has been formed by two or more different and contrasting processes so that all of the horizons are not genetically related.

Poorly Drained: SEE STRONGLY ANAEROBIC.

Pore Space: The continuous and interconnecting spaces in soils.

Pore: A discrete volume of soil atmosphere completely surrounded by soil (cf. PORE SPACE).

Porosity: The volume of the soil mass occupied by pores and pore spaces.

Preparation - treatment of materials prior to composting, including grinding, shredding, sorting and adding sewage sludge.

Primary Mineral: 1.A mineral such as feldspar or mica which occurs or occurred originally in an igneous rock. 2. Any mineral which occurs in the parent material of the soil.

Primary nutrient. The elements P, K and N. These must be taken up and utilized in sufficient quantities for plants to complete their life cycles. Normally present in quantities > 1%.

Profile: A vertical section through a soil from the surface into the relatively unaltered material.

Protein - constituent of living matter containing nitrogenous compounds.

Pseudomorph: A mineral having the characteristic outward form of another mineral or object it replaces.

Puddle: To destroy the structure of the surface soil by physical methods such as the impact of raindrops, poor cultivation with implements, and trampling by animals.

Putrescible Waste - organic materials prone to degrade rapidly, giving rise to obnoxious odors.
 
 

Q

Quaternary Era: The period of geological time following the Tertiary Era, it includes the Pleistocene and Holocene periods and extends from 2,000,000 - 0 years BP.
 
 

R

Rain Splash Erosion: SEE RAIN SPLASH.

Rain Splash: The redistribution of soil particles on the surface by the impact of rain drops. On slopes this can cause a large amount of erosion.

Rainfall Interception: The interception and accumulation of rainfall by the foliage and branches of vegetation.
 
 

Raised Beach: A beach raised by earth movement thus forming a narrow coastal plain. There may be raised beaches at different levels resulting from repeated earth movement.

Raw Humus: A humus form consisting predominantly of well preserved, though often fragmented plant remains with few fecal pellets.

Recalcitrant: Term generally applied to organic matter that is quite stable or nutrients that are stable and not subject to release into soluble form.

Reduction. The process of an element or compound accepting an electron during a chemical reaction. see OXIDATION.

Regolith: The unconsolidated mantle of weathered rock, soil and superficial deposits overlying solid rock.

Respiration - the metabolic function of consuming oxygen.

Restricting horizon: The soil horizon that most restricts movement of water or air movement vertically through the soil, or restricts root growth down into soil. Restricting horizons are often termed PANS.

Retention mechanism: The process by which a substance (i.e. nutrient) is retained within the soil profile. Examples include precipitation, adsorption, nutrient cycling, and binding into organic matter.

Rhizosphere: The soil close to plant roots where there is usually an abundant and specific microbiological population.

Rill Erosion: The formation of rills as a consequence of poor cultivation.

Rill: A small intermittent water course with steep sides.

Rubification: The development of red color in soil - reddening.

Runoff - precipitation that reaches the composting pad directly without going through the composting materials.
 
 

S

Saline Soil: A soil containing enough soluble salts to reduce its fertility.

Salinization: The process of accumulation of salts in soil.

Sand: Mineral rock fragments that range in diameter from 2-0.05 mm in the USDA system.

Saprist. Organic soils in which most of the plant matter has decomposed (less than 1/3 of fibers remain visible after rubbing) and the original tissue cannot be recognized.

Sater mark: See HIGH WATER MARK.

Saturated Flow: The movement of water in a soil that is completely filled with water.

Saturated soil. A soil for which the entire profile is saturated with water.

Sclerotia: Spherical resting stages of fungi.

Secondary Mineral: Those minerals that form from the material released by weathering. The main secondary minerals are the clays and oxides.

Secondary nutrient. The elements S, Ca, Mg. These must be taken up and utilized in sufficient quantities for plants to complete their life cycles. Normally present in quantities of 0.01-0.5 %. See essential element.

Sedimentary Rock: A rock composed of sediments with varying degrees of consolidation. The main sedimentary rocks include sandstones, shales, conglomerates and some limestones.

Self-Mulching Soils: A soil with a naturally formed well aggregated surface which does not crust and seal under the impact of raindrops.

Sesquioxides: Usually refers to the combined amorphous oxides of iron and aluminium.

Sheet Erosion: The gradual and uniform removal of the surface soil by water without forming any rills or gullies.

Silicates: Rock forming minerals that contain silicon.

Silt: Mineral particles that range in diameter from 0.02-0.002 mm in the international system or 0.05-0.002 mm in the USDA system.

Size Reduction - generic term for breaking up solid waste or other materials into small pieces through crushing, chipping, shredding, grinding, etc.; the process makes wastes easier to separate and increases surface area for composting.

Slickenside: The polished surface that forms when two peds rub against each other when some soils expand in response to wetting.

Slickspot: Small areas of surface soil that are slick when wet because of alkalinity or high exchangeable sodium.

Sludge: Solid residue of the wastewater purification process, a product of screening, sedimentation, filtering, pressing, bacterial digestion, chemical precipitation and oxidation; primary sludge is produced by sedimentation process and secondary sludge is the product of microbial digestion.

Slurry: A thin watery mixture of a fine insoluble material.

Soil Amendment/Soil Conditioner: Soil additive which stabilizes the soil, improves resistance to erosion, increases permeability to air and water, improves texture and resistance of the surface to crusting, eases cultivation or otherwise improves soil quality.

Soil Auger: A tool used for boring into the soil and withdrawing small samples for field or laboratory examination.

Soil Classification: See SOIL TAXONOMY

Soil Erratics: 1. Fragments of horizons or other soil features transported and incorporated in superficial deposits in which a soil may have formed or is forming. 2. Part of a previously existing horizon preserved within a subsequently formed horizon.

Soil Fabric: The arrangement, size, shape and frequency of the individual soil constituents, excluding pores.

Soil Horizon: SEE HORIZON.

Soil Monolith - A vertical section through the soil preserved with resin and mounted for display.

Soil Order. The highest level of soil classification. There are presently 12 soil orders, including 1) Entisols, 2) Inceptisols, 3) Spodosols, 4) Ultisols, 5) Alfisols, 6) Vertisols, 7) Oxisols, 8) Histosols, 9) Andisols, 10) Aridosols, 11) Mollisols, and 12) Gelisols.

Soil Profile - A section of two dimensions extending vertically from the earth's surface so as to expose all the soil horizons and a part of the relatively unaltered underlying material.

Soil Structure: See STRUCTURE

Soil Suborder. The 2nd highest taxonomic order of the U.S. soil classification system.

Soil Survey - The systematic examination and mapping of soil.

Soil Taxonomy - The systematic arrangement of soils into groups or categories on the basis of their characteristics.

Soil Textural Triangle - A 3-phase scale used to define soil into a soil textural group.

Soil Texture: The size distribution of individual particles of a soil.

Soil: (1) A dynamic natural body composed of mineral and organic materials and living forms in which plants grow. (2) The collection of natural bodies occupying parts of the earth's surface that support plants and that have properties due to the integrated effect of climate and living matter acting upon parent material, as conditioned by relief, over periods of time.

Solifluction - Slow flow of material on sloping ground, characteristic of , though not confined to regions subjected to alternate periods of freezing and thawing.

Solum - The part of the soil above the relatively unaltered material.

Sphericity: Relates to the overall shape of a feature irrespective of the sharpness of its edges and is a measure of the degree of its conformity to a sphere.

Spodic horizon. A subsurface soil horizon characterized by an accumulation of aluminum, (also potentially iron) and organic matter. This is the diagnostic horizon for the soil order Spodosol.

Spodosol. A soil order characterized by the presence of a spodic horizon.

Springtails: Very small insects that live in the surface soil and feed on organic matter.

Stability: state or condition in which the composted material can be stored without giving rise to nuisances or can be applied to the soil without causing problems there; the desired degree of stability for finished compost is one in which the readily decomposed compounds are broken down and only the decomposition of the more resistant biologically decomposable compounds remains to be accomplished.

Stabilization - stage in composting following active decomposition; characterized by slow metabolic processes, lower heat production and the formation of humus.

Strip Cropping: The practice of growing crops in strips along the contour in an attempt to reduce runoff, thereby preventing runoff or conserving moisture.

Strongly Anaerobic: (poorly drained) Soil that remains very wet or waterlogged for long periods of the year and as a result develops a mottled pattern of grays and browns.

Structure: The spatial distribution and total organization of the soil system as expressed by the degree and type of aggregation and the nature and distribution of pores and pore spaces.

Subhedral: Minerals with partly developed crystallographic form.

Suborder. See SOIL SUBORDER.

Symbiosis: Two organisms that live together for their mutual benefit. Fungus and alga that forms a lichen or nitrogen fixing bacteria living in roots are examples of symbiosis. The individual organisms are called symbionts.

Synergism - the simultaneous action of separate agencies which, together, create a greater total effect than the sum of their individual effects.
 
 

T

Talus: Angular rock fragments that accumulate by gravity at the foot of steep slopes of cliffs.

Tectonic: Rock structures produced by movements in the earth's crust.

Terrace: A broad surface running along the contour. It can be a natural phenomenon or specially constructed to intercept runoff, thereby preventing erosion and conserving moisture. Sometimes they are built to provide adequate rooting depths for plants.

Tertiary Period: The period of time extending from 75,000,000-2,000,000 years BP.

Texture - See SOIL TEXTURE

Texture Triangle - See SOIL TEXTURAL TRIANGLE

Thorn Forest: A deciduous forest of small thorny trees developed in a tropical semi arid climate.

Tile Drain: Short lengths of concrete or pottery pipes placed end to end at a suitable depth and spacing in the soil to collect water from the soil and lead it to an outlet.

Till Plain: A level or undulation land surface covered by glacial till.

Till: An unstratified or crudely stratified glacial deposit consisting of a stiff matrix of fine rock fragments and old soil containing sub-angular stones of various sizes and composition, many of which may be striated (scratched). It forms a mantle from less than 1 m to over 100 m in thickness covering areas which carried an ice sheet or glaciers during the Pleistocene and Holocene periods.

Tilth: The physical state of the soil that determines its suitability for plant growth taking into account texture, structure, consistence and pore space. It is a subjective estimation and is judged by experience.

Toposequence: A sequence of soils whose properties are determined by their particular topographic situation.

Topsoil: Soil consisting of various mixtures of sand, silt, clay and organic matter; considered to be the nutrient-rich top layer of soil that supports plant growth.

Toxic Substance: A substance that is present in the soil or the above ground atmosphere that inhibits the growth of plants and ultimately may cause deficiency symptoms or their death.

Toxicity: Adverse biological effect due to toxins and other compounds.

Toxin: Unstable poison-like compound of biological origin which may cause a reduction of viability or functionality in living organisms. see Toxic Substance.

Trace Metals: Trace elements regulated because of their potential for human, plant, or animal toxicity, including cadmium (Cd), copper (Cu), chromium (Cr), mercury (Hg), nickel (Ni), lead (Pb) and Zinc (Zn).

Traffic pan: Compacted soil horizon created by the action of machinery, such as trucks, tractors or logging skidders, over the soil.

Translocation: Migration of material in solution or suspension from one horizon to another.

Triassic: A period of geological time extending from 190,000,000-150,000,000 years BP.

Tropical Rain Forest: SEE EQUATORIAL FOREST
 
 

U

Ultisol. A soil order characterized by higher clay in the B-horizon than the A-horizon and an acid subsoil.

Ultramicropores: Pores <5mm in diameter.

Unavailable Nutrients: Plant nutrients that are present in the soil but cannot be taken up by the roots because they have not been released from the rock or minerals by weathering or from organic matter by decomposition.

Unavailable Water: Water that is present in the soil but can not be taken up by plant roots because it is strongly adsorbed onto the surface of particles.

Unconsolidated: Sediments that are loose and not hardened.

Unsaturated Flow: The movement of water in the soil that is not completely filled with water.

Upland. An area where soils are generally relatively well drained such that the water table is significantly below the soil surface most of the year.
 
 

V

Value: The relative lightness or intensity of color, one of the three color variables.

Varnish (Desert): A dark shiny coating on stones in deserts, probably composed of compounds of iron and manganese (cf. DESERT VARNISH)

Varve: A layer representing the annual deposit of sediment, it usually consists of a lighter and darker portion due to the change in rate of decomposition during the year. The material may be of any origin but the term is most often used in connection with glacial lake sediments.

Vector - animal or insect that transmits a disease-producing organism, including rats, mice, mosquitos, etc.

Ventifact: A pebble faceted or molded by wind action, usually formed in desert or polar areas. The flat facets meet at sharp angles.

Vermicomposting - the biological degradation of organic matter contained in agricultural, urban and industrial wastes, occurring when earthworms feed on these materials.

Vermiculture - composting by the activity of earthworms; material is eaten by the worms, leaving air passages which maintain aerobic conditions; the process is completed with a curing stage.

Very Poorly Drained: A soil that remains wet and waterlogged for most of the year so that most of the horizons are blue, olive or gray due to the reducing conditions.

Volatilization: gaseous loss of a substance to the atmosphere

Volcanic Ash (Volcanic Dust): Fine particles of lava ejected during a volcanic eruption. Sometimes the particles are shot high into the atmosphere and carried long distances by the wind.
 
 

W

Water-Table (Ground): The upper limit in the soil or underlying material permanently saturated with water.

Water-Table (Perched): SEE PERCHED WATER TABLE.

Waterlogged: Saturated with water.

Weakly Anaerobic: A horizon that is anaerobic for short periods and moist for long periods. The colors are less bright than aerobic horizons and they are usually marbled or weakly mottled.

Weathering: All the physical, chemical and biological processes that cause the disintegration of rocks at or near the surface.

Well Drained: SEE AEROBIC.

Wetland soil: see HYDRIC SOIL.

Wetland: General definition: Areas that under normal circumstances have hydric soils and hydrophytic vegetation. Legal and political definition: It should be noted that the specific legal definition of wetland is often hotly debated and wetland experts are working hard to come up with a good legal definition.

Wilting Point: The percentage by weight of water remaining in the soil when the plant wilts permanently.
 
 

X

Xerophytes: Plants that grow in extremely dry areas.
 
 

Y
 
 

Z