In fertilizer use, the 4Rs refer to (1) the right source of fertilizer, (2) the right rate of fertilizer, (3) the right timing of fertilizer application, and (4) the right placement of fertilizer to achieve efficient and timely uptake of fertilizer nutrients by growing crops. The goal is to properly nourish the crop and achieve the economically optimal crop yield, without any excess.

6C practices

Six management practices land managers can use to build soil health. The six C's are: 1. compaction reduction, 2. conservation tillage, 3. crop + animal diversity, 4. continuous living plants, 5. cover crops, and 6. compost + organic amendments. The letter C was purposefully chosen to emphasize the role of carbon in soil health.


Non-living, referring to the basic elements and compounds of the environment.


(physics) The process by which the energy of electromagnetic radiation is taken up by a molecule and transformed into a different form of energy. (chemistry) The process by which one substance is taken up by another substance.

acid mine drainage

Water contamination by sulfuric acid produced by seepage through sulphur-bearing spoil and tailings from coal and metal mining.


(total) The total acidity in a soil or clay, usually estimated by a buffered salt determination of [cation exchange capacity-exchangeable bases]=total acidity. Also approximated by the sum of salt replaceable acidity+residual activity. Often calculated by subtraction of exchangeable bases from the cation exchange capacity determined by ammonium exchange at pH 7.0. It can be determined directly using pH buffer-salt mixtures (e.g. BaCl2) plus triethanolamine, pH 8.0 or 8.2) and titrating the basicity neutralized after reaction with a a soil.

active acidity

The activity of hydrogen ions in the aqueous phase of a soil. It is the acidity immediately measured in the soil solution.

active layer

The top layer of soil in a permafrost zone, subjected to seasonal freezing and thawing which, during the melt season, becomes very mobile.


(chemistry) (1) A dimensionless measure of the deviation of the chemical potential of a substance from its value in some state which, for convenience, is chosen as a standard state. Defined by the equation: mu=mu^o + RT ln a, where mu is the chemical potential in a state in which the activity is a, mu^o is the chemical potential in the standard state (where a=1.0), R is the molar gas constant, and T is the absolute temperature. (2) The effective concentration of substance in a solution.

ad infinitum

To infinity.

adenosine triphosphate (ATP)

An energy storage compound common to all biological systems. The high-energy intermediate is formed during photosynthesis or by the breakdown of energy-containing material, such as glucose. Supplies the energy for many cellular reactions and functions.


(chemistry) A force that acts to hold the molecules of dissimilar substances together. The static attractive force at the contact surface between two bodies of different substances. (soil mechanics) The shearing resistance between soil and another material under zero externally applied pressure.


The process by which atoms, molecules, or ions are taken up and retained on the surfaces of solids by chemical or physical binding (e.g. the adsorption of cations by negatively charger minerals). The two types of adsorption are physiosorption, in which the attractive forces are purely van der Waals, and chemisorption, where chemical bonds are actually formed between the adsorbent (the material doing the adsorbing) and adsorbate (the material being adsorbed).


Organism requiring oxygen for growth.


(1) Having molecular oxygen as a part of the environment. (2) Growing only in the presence of molecular oxygen, such as aerobic organisms. (3) Occurring only in the presence of molecular oxygen, as applied to certain chemical or biochemical processes such as aerobic decomposition.

aerobic respiration

Cellular respiration utilizing O2 as the terminal electron acceptor.


Arrangement of primary soil particles (sand, silt, clay) around soil organic matter and through particle associations. Soil particles held in a single mass or cluster, such as a clod, crumb, block, or prism. Aggregate stability is a good indicator of soil health.


(also agro-environmental; agri-environmental): relating to the agricultural environment and the adjacent environments. In nutrient management, the agroenvironmental goal is to achieve the crop yield target without releasing excess nutrients into adjacent environments.


Land use system in which woody perennials are grown for wood production with agricultural crops, with or without livestock production.


Pertaining to alluvium.


Material (e.g., clay, silt, sand, and gravel) deposited by running water, including the sediments laid down in riverbeds, flood plains, lakes, and estuaries.

amendment (soil)

Any material added to a soil to improve its properties.


Not crystalline, or not apparently crystalline. A mineral solid that lacks the long-range order characteristic of a crystal. The internal order of chemical bonds and atoms are either random or very short order. Individual mineral grains are typically very small and produce either no X-ray diffraction pattern or ones with very broad low intensity peaks.

amorphous mineral

(1) A mineral that has no definite crystalline structure. (2) A mineral that has a definite crystalline structure but appears amorphous because of the small crystallite size. (3) A noncrystalline constituent that either does not fit the definition of allophane or it is uncertain that the constituent meets allophane criteria.

A mineral solid that lacks the long-range order characteristic of a crystal. The internal order of chemical bonds and atoms are either random or very short order. Individual mineral grains are typically very small and produce either no X-ray diffraction pattern or ones with very broad low intensity peaks.


One of the ferromagnesian silicate mineral group, characterized by prismatic, columnar, or fibrous crystals with a structure of cross-linked double chains of tetrahedra (e.g. horneblende).


(substance) A substance that can behave either as an acid or as a base. Materials that can be both positively and negatively charged. The proportion of the charge sites depends on the pH of the environment. Amphoteric minerals are generally positively charged at low pH and negatively charged at high pH values. Oxides or hydroxides that have surface hydroxyl groups (e.g., Al(OH)3 or goethite) are usually amphoteric.


The metabolic process involving the conversion of simpler substances to more complex substances or the storage of energy. More generally, the synthesis of organic compounds within an organism. Also called assimilation, biosynthesis, or constructive metabolism. See catabolism.


Organism that lives in the absence of air (oxygen).


(1) The absence of molecular oxygen. (2) Growing in the absence of molecular oxygen (e.g., anaerobic bacteria). (3) Occurring in the absence of molecular oxygen (e.g., a biochemical process).

anaerobic respiration

A metabolic process in which electrons are transferred from a reduced organic or inorganic compound to an inorganic acceptor molecule other than oxygen. The most common acceptors are carbonate, sulfate, and nitrate.

anion exchange

A process in which anions in solution are exchanged with anions held on positively charged exchange sites on the surfaces of mineral or organic particles.

anion exchange capacity (AEC)

The total number of exchangeable anions that a soil can adsorb. It is expressed as centimoles, or millimoles, of charge per kilogram of soil or other adsorbing material, such as clay.


Derived from human activities.


Azonal soils, highly modified or constructed by human activity, with one or more natural horizons removed, removed and replaced, added to, or significantly modified. Defining features are severe disruption of soil forming factors and introduction of potentially new pedogenic trajectories. Disturbed layers are anthropic in origin and contain materials significantly modified physically and/ or chemically by human activities.

arbuscular mycorrhizae

Mycorrhizal association with intracellular penetration of the host root cortical cells by the fungus as well as outward extension into the surrounding soil. Also known as endomycorrhiza.


a grouping or combination of entities. (ecology) A group of species occurring in the same place because of environmental requirements or tolerances. (soil science) A grouping of soils based on similarities in climatic or physiographic factors and soil parent materials.

Atterberg limits

see liquid limit and plastic limit

available water capacity (AWC)

The amount of water released between in situ field capacity and the permanent wilting point (usually estimated by water content at soil matric potential of -1.5 MPa).

base saturation percentage

The extent to which the adsorption complex of a soil is saturated with exchangeable cations other than hydrogen and aluminum; expressed as a percentage of the total cation exchange capacity.


The process of a steady buildup of a contaminant in an organism over its lifetime (also see biomagnification).


Inoculation of soil or other media with microorganisms to facilitate bioremediation; may refer to inoculation of a single organism or a group (consortium) of organisms.


In the context of bioremediation, refers to the relative availability of the contaminant to microbial decomposers or their enzymes; contaminants that are entrapped in soil aggregates or which are strongly sorbed to soil solids may have reduced bioavailability and may exhibit limited or slow biodegradation.


The state of a compound being easily taken up by an organism, typically referring to an energy or anabolic nutrient source, or a pollutant or toxicant.


A charcoal-like substance made by burning organic material from agricultural and forestry wastes in a controlled process called pyrolysis; e.g., at 300 to 700 °C under low oxygen conditions.


The biochemical conversion of a parent organic compound to simpler forms; may or may not be complete conversion to inorganic constituents.


The creation of channels through layers of soil compaction by plant roots. When left undisturbed, these channels allow the roots for subsequent crops to growth through the compaction layer.

biological control

A method of controlling pests or undesirable species by introducing or manipulating naturally occurring predatory organisms or their products, or by sterilizing them. In agriculture, biological control is used to reduce or replace mechanical or chemical means of controlling pests.

biological nitrogen fixation

The conversion of nitrogen gas in the atmosphere (N2) to a reduced organic form (e.g. ammonia and amino groups of amino acids) that can be used as a nitrogen source by organisms. Biological nitrogen fixation is carried out by a variety of organisms; however, those responsible for most of the fixation are certain species of blue-green algae, the soil bacterium Azotobacter, and the symbiotic association of leguminous plants and the bacterium Rhizobium.

The transformation of atmospheric N2 into ammonia (NH3) through the reaction N2 + 8 H+ + 16 ATP + 8 e- 🡪 2NH3 (g) + H2 + 16 ADP + 16 Pi . The reaction is mediated by symbiotic, associative and free-living soil prokaryotes that possess the nitrogenase enzyme.

biological treatments

Remediation strategies that facilitate growth of organisms, such as microorganisms and/or plants, to convert contaminants to non-hazardous or less toxic compounds or compounds which are more stable, less mobile, and/or inert.


The increase (often exponential) in tissue concentrations of contaminants up trophic levels in food webs to apex organisms.


A major biotic unit consisting of plant and animal communities formed by the interaction of regional climates with regional biota and substrates. A number of biomes and subtypes are recognized, including alpine biome, chapparral biome, desert biome, freshwater biome, grassland biome, marine biome, savannah biome, taiga biome, tundra biome, temperate deciduous forest biome, and tropical rainforest biome. Land-based biomes are called terrestrial biomes. Water-based biomes are called aquatic biomes.


Remediation strategies that use biological agents, such as microorganisms, to destroy, remove, or convert contaminants in soils, ground water or other contaminated media to less toxic forms.


Solid organic materials such as sewage sludges that undergone a sewage treatment process to lower pathogen risk, and used as a fertilizer amendment.


Addition of nutrients to stimulate microbial activity including biodegradation of contaminants; commonly added nutrients include nitrogen and phosphorus.


All living organisms of an area, taken collectively.


The disturbance of sedimentary deposits by living organisms.


Various solid and semi-solid hydrocarbons, most commonly applied to the heavy viscous hydrocarbons associated with the tar sands.

bottom-up processes

Trophic interactions in a community, where the level of a primary resource determines the population of consumers.


An order of soils in the Canadian system of soil classification in which the horizons are developed sufficiently to exclude the soils from the Regosolic order, but lack the degrees or kinds of horizon development specified for soils of the other orders. These soils, which occur under a wide variety of climatic and vegetative conditions, all have Bm or Btj horizons. The great groups Melanic Brunisol, Eutric Brunisol, Sombric Brunisol, and Dystric Brunisol belong to this order.

bulk density (ρb)

The mass of dry soil per unit bulk volume, thus often termed dry bulk density. Bulk volume is determined before the soil is dried to constant mass at 105 degrees C. Also called apparent density.

ρb = Ms / Vt  expressed in kg per cubic meter or g per cubic centimeter


Process of soil formation involving accumulation of calcium carbonate in the C, and possibly other,  soil horizons.


A layer near the soil surface that is cemented by secondary carbonates of calcium or magnesium precipitated from the soil solution. It may be a soft thin soil horizon, a hard thick bed just beneath the solum, or a surface layer exposed by erosion. It is not a geologic deposit.

Canada Land Inventory
Canada Land Inventory (CLI)

A comprehensive multi-disciplinary land inventory of rural Canada, covering over 2.5 million square kilometers of land and water.Includes land capability for agriculture, forestry, wildlife, recreation, wildlife (ungulates and waterfowl).
There are seven classes used to rate agricultural land capability, with Class 1 lands having the highest and Class 7 lands the lowest capability to support agricultural land use activities.

Canadian Shield

The 3.96 billion year old (2.5-4.2 Ga) ancient core of the North American continent. The exposed area is approximately 8,000,000 square kilometers and underlies eastern, central, and northwestern Canada and most of Greenland, extending south into the United States. The igneous and metamorphic rocks are relatively resistant to weathering and erosion but have be exposed to intense and repeated glaciation. Ice during the most recent glaciation, approximately 10,000 years ago, scraped off most of the soil and weathered rock, which was deposited south and southwest of the Shield. Average relief is 30 m, except in northern Labrador and Baffin Island, where it can reach up to 1,500 m.

capillary water

The 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.

carbon sequestration

The process of capturing and storing atmospheric carbon dioxide.


An animal that obtains its nourishment by eating other animals.


Metabolic processes involved in the breakdown of organic compounds, usually leading to the production of energy.


A group of soils that commonly occur together in a landscape, each characterized by a different slop position and resulting set of drainage-related properties.

cation exchange

A process in which cations in solution are exchanged with cations held on negatively charged exchange sites on the surfaces of mineral or organic particles.

cation exchange capacity (CEC)

The total amount amount of exchangeable cations that a soil can adsorb; sometimes called "total exchange capacity," "base exchange capacity," or "cation adsorption capacity". It is expressed in centimoles of charge per kilogram of soil or of other adsorbing material (e.g., clay).


The process by which clastic sediments are converted into rock by precipitation of a mineral cement among the grains of the sediment.

charge density

Amount of electric charge per unit length, surface area, or volume.


An organic chemical with two or more functional groups that can bind with metals to form a ring structure. The process is known as chelation. This protects the metal ions from being tied up in the soil in forms that plants cannot use.


Formation or presence of bonds (or other attractive interactions) between two or more separate binding sites within the same ligand (e.g., organic molecule) and a single central atom (e.g., transition metal). A molecular entity in which there is chelation is called a chelate.

chemical treatments

Remediation strategies that involve chemical conversion of contaminants to non-hazardous or less toxic forms, or to compounds which are less mobile or inert. Includes chemical oxidation, chemical reduction, and neutralization of acidic or basic media types. Chemical oxidation and reduction are generally more applicable to contaminated waters or to soil slurries with high water content.


An order of soils in the Canadian system of soil classification that have dark surface horizons high in organic matter (termed Ah horizons). The high organic matter levels result from addition of soil organic matter (SOM) through the roots of grasses and limited decomposition of the organic matter due to dry soil moisture conditions. Chernozemic soils can occur on all soil textures from heavy clay though to sands. The high SOM surface soil horizon is typically underlain by a B horizon which has undergone minor alterations due to chemical weathering (Bm horizon).

A grassland soil whose diagnostic horizon is formed by high levels of organic matter additions from the roots of grasses.

chloropleth map

a map that uses different shading or coloring, or places symbols within predefined areas to indicate average values of a specific property or characteristic within those areas.


(plural) Small hairlike projections found on the surface of some microorganisms and used for movement.


(1) A soil separate consisting of particles <0.002 mm in equivalent diameter. (2) A textural class. (3) A naturally occurring material, composed primarily of fine-grained minerals, which is generally plastic at appropriate water contents and will harden when dried or fired. Although clay usually contains phyllosilicates, it may contain other materials that impart plasticity and harden when dried or fired. Associated passes in clay may include materials that do not impact plasticity and organic matter.

clay mineral

A phyllosilicate mineral or a mineral that imparts plasticity to clay and hardens upon drying or firing.


The average weather (usually taken over a 30-year period) for a particular region and time period.

coarse fragments

Rock or mineral particles (harder than 3 on Mohs scale of hardness) larger than 2 mm in diameter. Coarse fragments in soils are gravel or channery (up to 8 cm in diameter or 15 cm in length), cobbles or flags (8 to 25 cm diameter or 15 to 38 cm length), and stones (greater than 25 cm diameter or 38 cm length).


The force holding a solid or liquid together, owing to attraction between like molecules. Cohesion and inter-granular friction are the forces that combine to give soil shear strength.


A particle 0.1 to 0.001 μm in diameter. Soil clays and soil organic matter are often called colloids because they fall within these size dimensions.


Interaction between two species in which one species derives benefit while the other is neither benefited nor harmed.


All the organisms that occupy a specific habitat and interact with one another in time and space.


(1) Increasing soil bulk density, and concomitantly decreasing soil porosity, by the application of mechanical or other forces to a soil. As soil compaction increases, a state of excessive compaction can be reached that adversely affects plant growth. (2) The mechanical reduction of the volume of solid waste (an increase in density) by the application of pressure.

complex ion

A charged species consisting of a metal ion surrounded by ligands (i.e., molecules or ions that donate a pair of electrons to a metal ion to form a complex).


Soil conditioner and fertilizers produced from organic residues or a mixture of organic residues and soil, that have been piled, moistened, and allowed to decompose; often called artificial manure or synthetic manure.

conservation tillage

Any tillage sequence, the object of which is to minimize or reduce loss of soil and water; operationally, a tillage or tillage and planting combination which leaves 30% or greater cover of crop residue on the surface.


(1) The resistance of a soil to deformation or rupture. (2) The degree of cohesion or adhesion of the soil mass. Terms used for describing consistence depend on soil moisture content: wet soil (non sticky, slightly sticky, sticky, and very sticky; non-plastic, slightly plastic, plastic, and very plastic); moist soil (loose, very friable, friable, firm, very firm, compact, very compact, and extremely compact); dry soil (loose, soft, slightly hard, hard, very hard, and extremely hard); cementation (weakly cemented, strongly cemented, and indurated). In engineering practice, consistency has the same meaning as consistence.


Any unit dominated by a single species. For example, any unit of vegetation dominated by a single species (biogeography).


An organism that gains energy by feeding on another organism. The place for a consumer in the food chain is defined by what it eats. Herbivores eat plants, and are primary consumers; a human can be a primary consumer by eating plants or a secondary consumer by eating an animal that feeds on plants.


Refers to any chemical substance whose concentrations exceed background concentrations or which is not naturally occurring in the environment or biosphere. Compare with pollutant.


Physical treatments (e.g., tillage, furrows, vegetation) along or nearly parallel to the contour of the land, rather than up and down a slope, to limit or prevent erosive flow of water.

controlled traffic

Tillage (and all activities) in which all operations are performed in fixed paths so that recompaction of soil by traffic (traction or transport) does not occur outside the selected paths (called tramlines).

conventional tillage

Tillage operations normally performed in preparing a seedbed for a given crop grown in a given geographical area.

cover crop

A crop used primarily for the purpose of protecting and improving the soil between periods of regular crop production, or between rows of permanent standing crops (e.g., orchards and vineyards).

crop rotation

The practice of growing different crops in a planned regular sequence or succession on the same land. Usually established for economic considerations, especially to aid in the control of insects and diseases, maintain soil fertility, and decrease soil erosion.

cropping system

A system comprised of soil, crop, weeds, pathogen, and insect subsystems that transforms solar energy, water, nutrients, labor, and other inputs into food, feed, fuel, or fiber. The cropping system is a subsystem of a farming system.

cryogenic soil

Soil that has formed under the influence of freezing soil temperatures.


Frost action that causes churning, heaving, and considerable structural modification of the soil and subsoil.

cumulic layer

A layer or layers of mineral material in organic soils. Either the combined thickness of the mineral layers is more than 5 cm or a single mineral layer 5-30 cm thick occurs. One continuous mineral layer more than 30 cm thick in the middle or bottom tier is a terric layer.


The removal of calcium ions from a soil by the process of leaching, in which calcium biocarbonate is carried away in solution. Decalcification proceeds downward from the surface and is thought to be an initial stage of podzolization and clay translocation.


A heterotrophic organism, chiefly a microorganism (bacteria or fungi), that breaks down the bodies of dead animals or parts of dead plants and absorbs some of the decomposition products while releasing nutrients usable by producers.


The breakdown of a complex material into simpler materials. The complex material can be organic or inorganic, and heat, sunlight, water, chemicals, or metabolism can cause the decomposition. Metabolic decomposition is carried out by decomposer organisms.


A change in a system that interferes with its capacity to maintain a maximum range of tolerances for life


Reduction of nitrate, nitrite to molecular nitrogen, or nitrogen oxides by microbial activity (dissimilatory reduction of nitrate) or chemical reactions involving nitrite (chemical denitrification). Microbial denitrification is an anaerobic respiratory process characteristic of facultative aerobic bacteria growing under oxygen-depleted conditions (denitrifying bacteria).


The removal of a proton from a chemical compound.


(1) Process of soil formation involving the chemical migration of silica out of the soil solum, leaving an accumulation of iron and aluminum oxides. Also called ferralitization, ferritization, allitization. (2) The removal of silica from rocks by chemical weathering or by reaction between a body of magma and surrounding wall rock (e.g., formation of lime silicates).


the complete degradation of a system to the point that it would have to be rebuilt to be useful, including changing of one ecosystem for development of another


Animal that feeds on particulate material derived from the remains of plants or animals, including large scavengers, smaller animals such as earthworms and some insects, and decomposers.


The independent or random movement of ions or molecules that tends to bring about their uniform distribution within a continuous system.

(of gas): movement of a gas (e.g., CO2) from an area of high concentration to low concentration due to a difference in the partial pressure of the particular gas

(of solutes): movement of a solute (e.g., K+) from an area of high concentration to an area of low concentration, tending to bring about a uniform distribution within the soil solution


An octahedral sheet, or a mineral containing such a sheet, that has two-thirds of the octahedral sites filled by trivalent ions such as aluminum or ferric iron.

diploid (2n)

Pertaining to cells or organisms having two sets of chromosomes.


(geology) (1) Any interruption in sedimentation; an unconformity. (2) A surface separating two unrelated groups of rocks (e.g., a fault).


(1) To break up compound particles, such as aggregates, into the individual component particles. (2) To distribute or suspend fine particles (e.g., clay) in or throughout a medium (e.g., water).


Variation in some ecosystem factor beyond its normal range resulting in ecosystem change.

duric horizon

A diagnostic B horizon that is strongly cemented and usually has an abrupt upper boundary and a diffuse lower boundary. Air-dry clods of duric horizon do not slake when immersed in water.

ecological niche

The physical space in a habitat occupied by an organism; its functional role in the community (e.g., its trophic position).

ecological pyramid

A visual representation, resembling a pyramid, that depicts the total mass of organisms residing in each trophic level in a given area. The bottom bar of the pyramid represents the mass of plants, the top bar represents the mass of carnivores, and intermediate bars represent other forms of biota in the feeding structure of the community.

ecological restoration

The process of assisting recovery and management of ecological integrity. Ecological integrity includes a critical range of variability in biodiversity, ecological processes and structures, regional and historical context, and sustainable cultural practices.


A functional unit consisting of all the living organisms (plants, animals, and microbes) in a given area, and all the non-living physical and chemical factors of their environment, linked together through nutrient cycling and energy flow.

ecosystem services

The tangible and intangible benefits humans gain from ecosystems (e.g., food, waste assimilation, aesthetic, nutrient cycling).


An area of the Earth's surface representative of large and very generalized ecological units characterized by interactive and adjusting abiotic and biotic factors. The ecozone defines, on a subcontinental scale, the broad mosaics formed by the interaction of macroscale climate, human activity, vegetation, soils, and geological and physiographic features of the country. Fifteen ecozones are recognized in Canada: Tundra Cordillera, Boreal Cordillera, Montane Cordillera, Boreal Plains, Taiga Plains, Prairie, Taiga Shield, Boreal Shield, Hudson Bay Plains, Mixed Wood Plains, Pacific Maritime, Atlantic Maritime, Southern Arctic, Northern Arctic, and Northern Cordillera.


A mycorrhizal association in which the fungal mycelia extend inward, between root cortical cells, to form a network, and outward into the surrounding soil. Usually the fungal hyphae also form a covering or mantle on the surface of the roots.


The potential generated between an oxidation and reduction half-reaction and the standard hydrogen electrode. In soils, it is the potential created by oxidation-reduction reactions that take place on the surface of a platinum electrode measured against a reference electrode minus the Eh of the reference electrode.

electrical conductivity (EC)

The reciprocal of electrical resistivity. The conductivity of electricity through water or an extract of soil; expressed in decisiemens or (dS m-1) siemens per meter at 25°C. It is a measure of soluble salts content in solution.

eluvial horizon

A soil horizon that has been formed by the process of eluviation.


The transportation of soil material in suspension or in solution within the solum by the downward or lateral movement of water.


Pertaining to materials deposited by wind.

Sediments generally consisting of medium to fine sand and coarse silt. They are well sorted, poorly compacted, and may show internal structures such as cross bedding or ripple laminae, or may be massive. These materials have been transported and deposited by wind action. (SCWG1998)

equivalent capability

The ability of land to support various uses after reclamation similar to that which existed prior to any activity being conducted on the land. However, the ability to support individual land uses will not necessarily be equal after reclamation.


Detachment and movement of soil by water, wind, ice, and/or gravity.


(geomorphology) A serpentine ridge of roughly stratified gravel and sand that was deposited by a stream flowing in or beneath the ice of a stagnant or retreating glacier and was left behind when the ice melted. Length ranges from less than 100 m to more than 500 km (including gaps), and in height from 3 m to more than 300 m.


A cell that has a membrane-bound nucleus, membrane-bound organelles, and chromosomes in which the DNA is associated with proteins; an organism composed of such cells.

ex situ

Off site, or away from the natural location. For example, a measurement or activity following the removal of a sample to a different location, such as a laboratory.

exchangeable sodium fraction

The fraction of the cation exchange capacity of a soil occupied by sodium ions.

exchangeable sodium percentage (ESP)

The exchangeable sodium fraction expressed as a percentage.

facultative anaerobe

(also facultative aerobe) The ability of certain organisms to harness energy from the environment under both aerobic and anaerobic conditions.

fallow land

Land not being used to grow a crop, but cultivated or left untilled during the whole or greater portion of the growing season to preserve water, kill weeds, and increase soil nutrients. In arid and semi-arid regions, a fallow year is commonly used in crop rotations.


(1) A group of  minerals of the general formula, M-Al(Al, Si)3O8, where M can be K, Na, Ca, Ba, Rb, Sr, or Fe. Feldspars are the most abundant of any mineral group, constituting about 60% of the Earth's crust and occurring in all types of rock. Feldspars are white and gray to pink, have a hardness of 6 (Mohs scale), are commonly twinned, have monoclinic or triclinic symmetry, and show good cleavage in two directions. (2) A mineral of the feldspar group, (e.g. microcline).


A type of bacterial or yeast metabolism (chemical reaction) characterized by the conversion of carbohydrates to acids or alcohols, usually occurring in the absence of molecular oxygen.


Any organic or inorganic material (other than liming material) of natural or synthetic origin that is added to a soil to supply elements essential to plant growth.


Organic materials that are readily identifiable as to botanical origin. Fibric material usually is classified on the von Post scale of decomposition as class 1 to class 4. (SCWG 1998)

field capacity (FC)

For agronomic purposes, the in situ content of water, on a mass or volume basis, remaining in a soil two or three days after having been wetted with water and after free drainage becomes negligible. Often called field water capacity.

fine earth

The fraction of mineral soil consisting of particles <2 mm in equivalent diameter.


(1) The process or processes in a soil by which certain chemical elements essential for plant growth are converted from a plant-available, soluble, or exchangeable form to a much less plant-available, soluble, or exchangeable form (e.g., phosphate fixation). (2) The reaction that occurs when ions moves into the inter-lattice of an expanding lattice clay. This is more likely with K+ and NH4+ due to their 1+ charge and relatively small ionic radius.


A flexible, whiplike appendage on cells, used as an organ of locomotion (plural flagella).


The process by which small particles or colloids coagulate due to the presence of ions in solution. In most soils the clay and humic materials remain flocculated due to the presence of divalent and trivalent cations.


Descriptive of materials transported and deposited by flowing water; growing or living in a stream or river; produced by the action of a stream or river.

food web

The interrelationship among the organisms in a soil community according to the transfer of useful energy from food resources to organisms eating those resources.


(1) Edible parts of plants, other than separated grain, that can provide feed for grazing animals or can be harvested for feeding, including browse, and herbage. (2) To search for or to consume forage (of animals).

formula unit

The empirical formula of any solid compound used as an independent entity for stoichiometric calculations. Typically equivalent to a “unit half-cell” (see unit cell).


A descriptor of consistence, pertaining to the ease by of crumbling soils.


A chemical compound in the form of a gas, particulate, vapor, or smoke, usually used to kill pests (e.g., fungi, insects, or rodents).


A species that has very a broad feeding niche (e.g., a consumer in soil that will feed upon multiple types of living plant tissues or detritus as well as fungal hyphae).


The scientific discipline concerned with using various mathematical and statistical techniques, and the development of new topographic variables, to analyze land surfaces.


Descriptive of material moved by glaciers and subsequently sorted and deposited by streams flowing from the melting ice. The deposits are stratified and may occur in the form of outwash plains, deltas, kames, eskers, and kame terraces.


Pertaining to, derived from, or deposited in glacial lakes; especially said of the deposits and landforms composed of suspended material brought by meltwater streams flowing into lakes bordering the glacier, such as deltas, kame deltas, and varved sediments.


Descriptive of compact, unstratified, silty to clayey sediments laid down in near-shore environments during glacial recession that were subsequently exposed through isostatic rebound. Deposits contain variable amounts of stones, gravels, and cobbles released from floating ice; and these coarse fragments are embedded in the fine-textured matrix of these deposits.


Reduction of Fe3+ to Fe2+ under anaerobic conditions and transfer of Fe2+.


An order of soils in the Canadian system of soil classification developed under wet conditions and permanent or periodic reduction. These soils have low chromas, or prominent mottling, or both, in some horizons. The great groups Gleysol, Humic Gleysol, and Luvic Glaysol are included in the order.

gleyzation, gleysation

A soil-forming process, operating under poor drainage conditions, which results in the reduction of iron and other elements and in gray colors and mottles.

gravimetric water content

(θw) is the ratio of water mass to dry soil mass, i.e., θw = Ml / Ms commonly expressed in g g-1.

gravitational potential

The amount of work that must be done per unit quantity of soil water in order to transport it reversibly and isothermally, from a pool at a specified elevation and at atmospheric pressure to a similar pool at the elevation of the point under consideration.

gravitational water

Water that moves into, through or out of the soil by gravity.

green manure

Any crop or plant grown and plowed under when green or soon after maturity to improve the soil by adding organic matter and subsequently releasing plant nutrients, especially nitrogen.


That portion of the water below the surface of the ground at a pressure equal to or greater than atmospheric (i.e., always saturated or below the water table). Water that is passing through or standing in the soil and the underlying strata. It is free to move by gravity.

groundwater discharge

The removal of water from the saturated zone across the water-table surface, together with the associated flow toward the water table within the saturated zone. (Freeze and Cherry 1979)

haploid (n)

A cell or organism that contains a single set of chromosomes.

heat capacity

The amount of heat required to raise the temperature of a unit volume of soil by one degree. It may also be expressed in terms of mass of soil, in which case it is called specific heat.


A consumer that eats plants or other photosynthetic organisms to obtain its food and energy.


An organism able to derive carbon and energy for growth and cell synthesis by utilizing organic compounds.

horizon (soil)

A layer of soil or soil material approximately parallel to the land surface in most cases; it differs from adjacent layers by physical (e.g., color, structure, texture, consistence) and/or chemical (e.g., pH) properties and mineralogical composition. Soil horizons in various soil classification systems are designated by a capital letter, with or without a lower case letter and/or number indicating a subdivision, or a numerical annotation (e.g., Ah horizon A1 horizon, Bt horizon).

horizontal gene transfer

The movement of genetic material by means other than parent to offspring.


Processes involved in the decomposition and partial stabilization of organic matter and leading to the formation of humus.


(1) The fraction of the soil organic matter that remains after removal of macroorganic matter and dissolved organic matter. It is usually dark-colored. (2) Also used in a broader sense to designate the humus forms referred to as forest humus. (3) All the dead organic material on and in the soil that undergoes continuous breakdown, change, and synthesis.

hydraulic conductivity (K)

The rate at which water can pass through a soil material under unit gradient; it is the proportionality factor (K) in Darcy's law as applied to the viscous flow of water in soil (i.e., the flux of water per unit gradient of the hydraulic potential). It depends on the intrinsic permeability of the medium and the fluid properties (mass density , viscosity). If conditions require that the viscosity of the fluid be separated from the conductivity of the medium it is convenient to define the permeability of the soil.


The tendency for a soil or soil particle to resist hydration, usually quantified using the water drop penetration time test.

hygroscopic water

(1) Water adsorbed by a dry soil from an atmosphere of high relative humidity. (2) Water lost from an air-dry soil when it is heated to 105 °C. (3) Water held by the soil when it is at equilibrium with an atmosphere of a specified relative humidity at a specified temperature, usually 98% relative humidity at 25°C. This is considered an obsolete term.


(plural) Branching filament structures in soil fungi and actinobacteria. The aggregated structures of hyphae are called mycelia.

illuvial horizon

A soil horizon in which material carried from an overlying layer has been precipitated from solution or deposited from suspension as a layer of accumulation.


The process of deposition of soil material removed from one horizon in the soil to another, usually from an upper to a lower horizon in the soil profile. Illuviated substances include silicate clay, hydrous oxides of iron and aluminum, and organic matter.


The conversion of an element from the inorganic to the organic form in microbial or plant tissue, thus rendering the element not readily available to other organisms or plants.

in situ

In the natural or original position. For example, a measurement taken in the field, without removal of a sample to the laboratory.


The entry of water into the soil.


Sowing [or growing] two or more crops simultaneously [often] in alternate rows.

ionic bonding

The electrostatic attraction between oppositely changed ions.

isomorphous substitution

The replacement of one atom by another of similar size in a crystal structure without disrupting or seriously changing the structure. Occurs during the formation of the mineral. When a substituting cation is of a smaller valence than the cation it is replacing, there is a negative charge on the structure. This commonly occurs in phyllosilicates where Al substitutes for Si in tetrahedral sheets and Mg or Fe substitute for Al in octahedral sheets. This substitution usually results in a charge deficit within the structure forming a surface charge site for cation exchange.

isostatic rebound

The rise of land masses that were depressed by the huge weight of ice sheets during the last ice age.


An individual for which selection is strong for relatively few well-developed offspring that have a good chance of surviving and reproducing; presumed to be important when competition is intense.


(K-selected species; from logistic growth curve equation referring to maximum carrying capacity of the ecosystem) Species that are characterized by having few, slower slow-growing and long-lived offspring that flourish in stable environmental conditions.


(geomorphology) A mound, knob, or short irregular ridge, composed of stratified sand and gravel deposited by a sub-glacial stream as a fan or delta at the margin of a melting glacier, by a supraglacial stream in a low place or hole on the surface of the glacier, or as a ponded deposit on the surface or at the margin of a stagnant ice.


(1) Pertaining to lakes. (2) Descriptive of materials that either have settled from suspension in bodies of standing fresh water or have accumulated at their margins through wave action.

land reclamation

The process of converting disturbed or damaged land to its former or other productive uses.


A soil-forming process in the humid tropics leading to soils with a low silica/sesquioxide ratio in the clay fractions, low clay activity, low content of most primary minerals and soluble constituents, a high degree of aggregate stability, and usually red in color.


Removal of soluble material from the soil by the downward movement of water.


A plant of the botanical family Leguminosae, (e.g., pea or bean), which has the ability to fix atmospheric nitrogen through a symbiotic association with nodule-forming bacteria of the genus Rhizobium.


A member of the mica group of minerals with chemical formula K(Li,Al)3(Al,Si,Rb)4O10(F,OH)2


The process by which clay minerals are moved mechanically downward through a soil by percolating water, leading to illuviation in a lower horizon. Evidence of lessivage is the gradual appearance with increasing depth of clay skins on the soil peds.


Organism resulting from the symbiotic relationship between a fungi and algae or cyanobacterium. They live in a wide range of habitats, from desert to polar regions and the tropics, but are commonly found in barren environments, and are dominant in tundra regions and mountains. Lichens are very sensitive to air pollution and serve as an indicator species. They occur in one of four basic growth forms: crustose- crustlike, growing tight against the substrate; squamulose- tightly clustered and slightly flattened pebble-like units; foliose- leaflike, with flat sheets of tissue not tightly bound; fruticose- free-standing branching tubes.


(chemistry) Calcium oxide (CaO). (agriculture) A soil amendment containing calcium carbonate, magnesium carbonate, and other materials, used to neutralize soil and furnish calcium and magnesium for plant growth.

liquid limit

One of the Atterberg limits. (1) The water content corresponding to an arbitrary limit between the liquid and plastic states of consistence of a soil; the upper plastic limit. (2) The water content at which a pat of soil, cut by a standard-sized groove, will flow together for distance of 12 mm under the impact of 25 blows in a standard liquid-limit apparatus.


Material transported and deposited by wind and consisting of a homogeneous, non-stratified, unindurated deposit made up predominantly of silt, which smaller amounts of very fine sand and/or clay.


(1) The increase in volume of voids in soils by plant, animal, and human activity, by freeze-thaw or other physical processes, and by removal of materials by leaching. (2) Decreasing soil bulk density and increasing porosity due to the application of mechanical forces to the soil.


An order of soils in the Canadian system of soil classification derived from underlying sedimentary rocks or on clayey lacustrine deposits (the latter primarily in the Boreal Shield Ecoregion). The diagnostic feature of Luvisolic soils is a textural contrast between the A and the B horizon the Ae horizon has less clay than the Bt horizon, which is presumed to arise from the physical transfer of clay from the Ae to the Bt horizon (termed lessivage) by vertically draining soil water.


Large pores (diameter > 0.08 mm) that occur between aggregates or between individual sand grains in coarse textured soil. They allow movement of air and the drainage of water, and accommodate roots and small animals to inhabit the soil. Also called aeration pores.


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 unit

(1) A conceptual group of one to many delineations identified by the same name in a soil survey that represent similar landscape areas comprising the same kind of component soil, plus inclusions; two or more kinds of component soils, plus inclusions; component soils and miscellaneous area, plus inclusions; two or more kinds of component soils that may or may not occur together in various delineations but all have similar, special use and management, plus inclusions; or a miscellaneous area and included soils. (2) Sometimes called a delineation.


(1) Pertaining to the sea. (2) Descriptive of materials that have settled from suspension in salt or brackish waters, or have accumulated at the margins of these waters through shoreline processes such as wave action and longshore drift.

mass flow

(nutrient) The movement of solutes associated with the net movement of water.

(soil solution) When an entire mass of soil solution moves from high to low pressure potential.

matric potential

The amount of work that must be done per unit quantity of soil water in order to transport it reversibly and isothermally from a pool at the elevation and the external gas pressure of the point under consideration to the soil water. The matric potential results from capillarity and adsorptive forces.


The process of nuclear division in a cell by which the chromosomes are reduced to half their original number; occurs during the formation of sex cells.


Darkening of A horizon material by addition and mixing of soil organic matter.


(1) A soil temperature regime that has mean annual soil temperate 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. (2) Mesic peat is organic material at a stage of decomposition between that of fibric and humic materials; peat soil material with >10% and <40% rubbed fibers. Mesic material usually is classified in the von Post humification scale of decomposition as class 5 or 6.


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


Having a state of apparent equilibrium although capable of changing to a more stable state.


Biological production of the reduced simple hydrocarbon (and atmospheric greenhouse gas) methane (CH4); carried out by anaerobic members of the domain Archaea using a limited number of simple substrates that are produced by symbiotic fermentative bacteria.


A microbe that consumes methane (CH4). Typically, in soils methanotrophs are aerobic lithotrophic bacteria that gain carbon for anabolism and energy from CH4. Soil methanotrophs in wetlands prevent the release of CH4 to the atmosphere, while in upland soils, methanotrophs are sinks for atmospheric CH4.


A layer-structured aluminosilicate mineral group of the 2:1 type characterized by its non-expandability and high layer charge, which is usually satisfied by potassium. The major types are muscovite, biotite, and phlogopite.


Small pores (diameter < 0.08 mm) that occur within soil aggregates or between clay particles in fine textured soils. They are usually filled with water and are too small to permit significant air movement. Also called water retention pores.

microbial biomass

The total mass of living microorganisms in a given volume or mass of a particular environment such as soil.

microbial biomass turnover

Determined by microbial cell production and cell death.

microbial grazers

Consumers that feed on decomposers or plant pathogens.


(1) A naturally occurring homogeneous solid, inorganically formed, with a definite chemical composition and an ordered atomic arrangement. (2) An economic mineral deposit exploited by mining.


(biochemical) The conversion of an organic substance to an inorganic form, often as a result of microbial decomposition. Gross mineralization is the total amount converted, and net mineralization, the gross minus the growth demand or immobilization by the decomposer organisms, usually measured in laboratory incubations.


The process of cell division involving the replication and division of the cell nucleus; results in two genetically identical cells.


A type of forest humus made up of plant remains partly disintegrated by the soil fauna, but not matted as in raw humus. It is a transitional form of humus between mull and mor. Also called duff mull.


(1) The repetitive growing of the same crop on the same land, season after season. (2) The cultivation of a single crop.


A type of forest humus distinguished by a matted F layer and a holorganic H layer with a sharp delineation from the A horizon. It is generally acid, and has high organic carbon content (52% or more) and a high C:N (usually 25 to 35 but sometimes higher). Various subgroups of mor can be recognized by the morphology, as well as chemical and biological properties.


Relating to material deposited by glacial ice. Their structure varies from relatively loose near the surface, to very compact at depth.


(geology) An accumulation of heterogeneous rubbly material, including angular blocks of rock, boulders, pebbles, and clay, that has been transported and deposited by a glacier or ice-sheet.

motile (motility)

Capable of movement.


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


Highly decomposed organic material in which the original plant parts are not recognizable. Contains more mineral matter and is usually darker in color than peat.


(1) A layer of dead plant material on the soil surface.
(2) An artificial layer or material such as paper or plastic on the soil surface.

mulch tillage

A system of tillage and planting operations which maintains a substantial amount of plant residues or other materials are left to cover the surface; also called mulch farming, trash farming, stubble mulch tillage, plowless farming; operationally, a full-width tillage or tillage and planting combination that leaves > 30% of the surface covered with crop residue.


A type of forest humus 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. 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. It is a kind of Ah horizon, wherein various subgroups can be distinguished by morphology and chemical characteristics. Mull is a diagnostic layer in the Canadian system of soil classification, where it is defined as having an organic matter content of 5 to 25% and a C:N of 12 to 18.


An interaction between two or more distinct biological species in which all members benefit from the association. Symbiotic mutualism requires an intimate association between species in which neither can carry out a required function alone. Non-symbiotic mutualism, also called protocooperation, is a beneficial but not obligatory relationship between organisms (i.e., the organisms are capable of independent existence).


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


The association, usually symbiotic, of fungi with the roots of seed plants. Under favourable soil conditions, plants with mycorrhizae have been shown to produce up to four or five times as much growth as similar plants without mycorrhizae. The mycorrhizae absorb water and nutrients and pass them on to the plant, secrete hormones that stimulate plant growth, and help protect the plant roots from disease organisms. In return, the fungi depend on the plant for carbohydrates.

mycorrhizal fungi

The fungal partners in mycorrhizae.


A system whereby a crop is planted directly into the soil with no primary or secondary tillage since harvest of the previous crop; special seeding equipment is necessary to prepare a narrow, shallow seedbed immediately surrounding the seed being planted. No-till is sometimes practiced in combination with subsoiling to facilitate seeding and early root growth, whereby the surface residue is left virtually undisturbed except for a small slot in the path of the subsoil shank.

non-point source

Non-point sources pollutants are emitted or released over a broad area.

nucleic acid

An organic acid composed of purine and pyrimidine bases, sugars, and phosphoric acid joined into nucleotide complexes. Biopolymers present in all organisms responsible for genetic coding and storage, gene expression, protein synthesis, and even some catabolic activities. Nucleic acids encompass ribonucleic acid polymers (RNA) deoxyribonucleic acid polymers (DNA).


Any substance that an organism obtains from its environment to supply energy and growth, or contribute to biomass production; most often used to identify substances use for growth by plants.

nutrient stewardship

An approach that requires prudent and judicious use of all fertilizers, considering that soil fertility derives from the soil nutrient supply, crop residues, historical manure applications, on-farm nutrient sources and commercial fertilizers.


A general term used for members of the isomorphous series forming the olivine group. A continuous series of solid solutions ranging from a silicate of magnesium, Mg2SiO4, to a silicate of iron, Fe2SiO4. The general formula is M+2SiO4 where M+2 is Fe, Mg, Mn, or Ni. Olivine is a component of basic rocks and ultrabasic rocks, and occasionally of acid rocks. It is usually dark green in color and exhibits no cleavage.

organic farming

Crop production systems that attempt to rely solely on organic matter or natural materials for crop production. They avoid and largely exclude the use of synthetic fertilizers, pesticides, growth regulators, and livestock feed additives. Organic farming relies instead on crop rotations, crop residues, animal manures, legumes, green manures, off-farm organic wastes, mechanical cultivation, mineral-bearing rocks, and biological pest control to maintain soil productivity and tilth, to supply plant nutrients, and to control insects, weeds, and other pests.

organic matter, soil

The organic fraction of the soil; includes plant and animal residues at various stages of decomposition, cells and tissues of soil organisms, and substances synthesized by the soil population. It is usually determined on soil that has passed through a 2.0 mm sieve.

organic soil

A soil composed predominantly of organic matter, in contrast to a mineral soil.


Any living or once-living thing.

osmotic potential

The amount of work that must be done per unit quantity of pure water in order to transport it reversibly and isothermally from a pool of pure water, at atmospheric pressure, to a pool of water identical in composition with the soil water at the same elevation as the point under consideration.


Material of any nature, consolidated or unconsolidated, that overlays a deposit of useful materials, ores or coal, especially those deposits that are mined from the surface by open cuts.

oxy-hydroxide mineral

See sesquioxide.


An ancient soil or a buried soil horizon formed during the geologic past.


The process of peat accumulation leading to peatland formation over previously forested land, grassland, or even bare rock, due to climatic or autogenic processes. A characteristic feature is the development of anaerobic conditions due to water logging.


Accumulation of organic materials under anaerobic conditions (Organic soils).


Interactions between species where one benefits and one is harmed.

parent material, genetic material

The unconsolidated and more or less chemically weathered mineral or organic matter from which the solum of a soil has developed by pedogenic processes. The classes of genetic materials for unconsolidated mineral materials used in soil surveys in Canada are anthropogenic, colluvial, eolian, fluvial, lacustrine, marine, morainal, saprolite, volcanic ash, and undifferentiated; and for the organic materials there are bog, fen, swamp, and undifferentiated organic material.

particle density

The mass per unit volume of the soil; usually expressed in Mg per cubic meter. Sometimes called grain density.


A microorganism, such as a bacterium or fungus, that has the capacity to cause disease under normal conditions.


Material constituting peatland, exclusive of live plant cover, consisting largely of organic residues accumulated as a result of incomplete decomposition of dead plant constituents under conditions of excessive moisture (e.g., submergence in water and/or water-logging).


The study of soils that integrates their distribution, formation, morphology, and classification as natural landscape bodies.


A branch of soil science that applies mathematical and statistical approaches for understanding the variability and distribution of soil.


It is the smallest, three-dimensional unit at the surface of the earth that is considered as a soil. Its lateral dimensions are 1 m if ordered variation in genetic horizons can be sampled within that distance or if these horizons are few and faintly expressed.

percolation (of soil water)

The downward movement of water through the soil; specifically, the downward flow of water in saturated or nearly saturated conditions at hydraulic potential gradients of 1.0 or less.


A condition existing below the ground surface, irrespective of its texture, water content, or geological character, in which the temperature in the material has remained below 0°C continuously for more than a year and, if pore water is present in the material, a sufficiently high percentage is frozen to cement the mineral and organic particles. The term describes permanently frozen ground, but permafrost has been subdivided into continuous and discontinuous permafrost, while sporadic permafrost is confined to alpine environments.

permanent wilting point (PWP)

For agronomic purposes, the soil water content associated with wilting of test plants (that do not recover under humid conditions) as a measure of the lower end of the plant available water. Often estimated by the water content at a soil matric potential of -1.5 MPa.


Any organism regarded as harmful, irritating, or offensive to humans, either directly or indirectly through its effect on animals and plants; the term is typically applied to rats and other rodents, insects that transmit disease or destroy crops, and pathogenic fungi and bacteria. In agriculture and forestry, a pest is any agent designated as detrimental to the health of vegetation or animals and which impedes effective resource management.

petroleum hydrocarbon (PHC)

The name given to a very broad range of chemicals that comprise oil and products refined from oil, such as gasoline and diesel.

A complex mixture of chemicals composed of hydrogen and carbon that are derived from crude oil, with a carbon content of 83 to 87%, a hydrogen content of 11 to 14%, and minor amounts of oxygen, nitrogen, sulfur, and traces of metals (e.g., lead). The mixture is found in various geological deposits and can be refined to produce such products as gasoline, fuel oil, kerosene, and asphalt.


An organism capable of utilizing light energy for growth; an organism that uses sunlight as its primary energy source for the synthesis of organic compounds. The word photoautotroph is a combination of autotroph, the word for an organism that makes its own food, and the prefix photo-, which means “light”.


A class or structural type of silicate in which the SiO4 tetrahedra are lined together in infinite two-dimensional sheets and are condensed with layers of AlO or MgO octahedral in the ratio 2:1 or 1:1. Also called layer silicate minerals.

physical treatments

Remediation strategies that use physical properties of contaminants or contaminated media to separate, remove, or immobilize the contamination.


Use of macroscopic plants to extract, degrade, contain, or immobilize contaminants in soil, ground water and other contaminated media.


The promotion of plant root growth facilitated by compounds released by rhizosphere microorganisms.

placic horizons

These horizons are thin (commonly 5 mm or less) or are series of thin layers that are irregular. hard, impervious, often dark reddish to black. They may be cemented by Fe, Al-organic complexes, hydrated Fe oxides, or a mixture of Fe and Mn oxides.


the shape of an object viewed from above.

plant available water

See available water storage capacity (AWSC).

plant growth promoting rhizobacteria (PGPR)

Rhizobacteria (bacteria from the rhizosphere and rhizoplane) that colonize plant roots and stimulate plant growth. They enhance plant growth directly (e.g., biological nitrogen fixation) or indirectly by protecting plants from disease and abiotic stresses such as drought.

plastic limit

One of Atterberg limits. The minimum water mass content at which a small sample of soil material can be deformed without rupture; the lower plastic limit.

plow pan

A subsurface soil layer, of varying thickness, which has a higher bulk density and lower total porosity than the soil material immediately above or below it. Normally occurs just below the maximum depth of tillage and is related to pressure from tractor tires and tillage implements. Also called plow sole.


A primary broadcast tillage operation performed to shatter soil with partial to complete inversion.


An order of soils in the Canadian system of soil classification having podzolic B horizons (Bh, Bhf, or Bf) in which amorphous combinations of organic matter (dominately fulvic acid), Al, and usually Fe are accumulated. The sola are acid and the B horizons have a high pH-dependent charge. The great groups in the order are Humic Podzol, Ferro-Humic Podzol, and Humo-Ferric Podzol.


A process of soil formation resulting in the genesis of Podzolic soils; it involves the translocation of Fe and/or Al organic matter complexes from the A horizon to the B horizon, resulting in the concentration of silica in the layer eluviated.

point source (pollution)

An identifiable and confined source of pollution, from which the pollutant is emitted or released into the environment. Non-point sources are the opposite, in which the pollutant is emitted or released over a broad area.


A chemical or material out of place or present at higher concentrations that has adverse effects on organisms.


a closed geometric figure used to graphically represent area features with associated attributes.

polymerase chain reaction (PCR)

An in-vitro method for amplifying defined segments of DNA. PCR involves a repeated cycle of oligonucleotide hybridization and extension on single-stranded DNA templates.


Minerals with the same chemical composition but different crystal forms.


a group of contiguous similar pedons. The limits of a polypedon are reached at a place where there is no soil or where the pedons have characteristics that differ significantly.


(biology) All individuals of a species living in defined geographical area at the same time in association with each other.


A void or space in a soil or rock not occupied by solid mineral material. The part of the bulk volume of soil not occupied by soil particles. Also called interstices or voids.

pore-size distribution

The volume fractions of the various size ranges of pores in a soil, expressed as percentages of the soil bulk volume (soil particles plus pores).

porosity (f)

The volume percentage of the total bulk soil occupied by voids; f = Vf / Vt  = (Vt - Vs) / Vt  expressed in cm3 cm-3 or %.

primary producers

Autotrophic organisms in an ecosystem, i.e., those capable of reducing the carbon molecule in CO2 to form new organic carbon molecules such as sugar. Primary producer biomass serves as the energy and carbon input to an ecosystem, fuelling all subsequent consumption.

profile (soil)

a vertical section of the soil through all its horizons and extending into the parent material.


Single cellular organisms that typically lack internal membrane-bound organelles, and notably, never contain nuclei. Members of the domains of life Bacteria and Archaea are prokaryotes.


The addition of a proton to an atom, molecule, or ion.


The edible seeds of any leguminous plant.


The thermal destruction of some material (e.g., coal, oil, wood, or other organic substance) in the absence of molecular oxygen. Also called destructive distillation.


A group of common rock-forming minerals with the general formula ABSi2O6, where A is chiefly Mg, Fe+2, Ca, or Na, and B is Mg, Fe+2, or Al. Colors include white, yellow, green, brown, and greenish black; specific gravity ranges from 3.2 to 4.0; and hardness ranges from 5 to 7 (Mohs sclae). Pyroxene occurs as stout prismatic crystals and in massive form in igneous and high temperature metamorphic rocks rich in Mg and Fe.


The crystalline form of silicon dioxide (SiO2). It is lustrous and sufficiently hard to scratch glass. In its most common form it is transparent and uncolored, but there are several varieties, including amethyst, yellow quartz (citrine), rose quartz, rock crystal (watery quartz), and smoky quartz (cairngorm).


Individuals that have been selected for high reproductive rates; presumed to be important in colonization or when competition is not intense.


(r-selected species; from logistic growth curve equation referring to growth rate) Species that are characterized by having high growth rates, producing many offspring and flourish in resource-rich, less-crowded conditions that are unstable or fluctuating in environmental conditions.


A representation of spatial data, which consists of a uniform grid of two-dimensional cells.

redox potential

An expression of the oxidizing or reducing power of a solution.


An order of soils in the Canadian system of soil classification most commonly associated with landforms where the land surface is (or has recently been) unstable. Because of the unstable surface, the soil has had little time to develop, and hence soil horizons are very weakly expressed if present at all.


Improvement of a contaminated site, including contaminated soil, to prevent, minimize, or mitigate damage to human health or the environment.

reserve acidity

Acidity associated with the exchange sites.


A metabolic process in an individual cell, tissue, or organism resulting in the release of chemical energy derived from chemically reduced organic or inorganic nutrients. Specifically, a series of reactions in a cell during which electrons removed during the oxidation of reduced substrates are transferred to an terminal acceptor.


(land reclamation) The establishment of vegetation that replaces original ground cover following land disturbance.


Any material released into soil from plant roots; includes water-soluble exudates, secretions of insoluble materials, lysates, dead fine roots, and gases.


The area of soil immediately surrounding plant roots in which the kinds, numbers, and activities of microorganisms differ from that of the bulk soil.

ridge tillage

A tillage system in which ridges are reformed atop the planted row by cultivation, and the ensuing row crop is planted into ridges formed in the previous growing season.


A coherent, consolidated, and compact mass of mineral matter. It can be an aggregate of one or more minerals (e.g., granite, shale, marble), a body of undifferentiated mineral mater (e.g., obsidian), or solid organic material (e.g., coal).

saline soil

A nonsodic soil containing enough soluble salts to interfere with the growth of most crop plants. The conductivity of the saturation extract is >4 dS m-1 at 25°C, the exchangeable sodium percentage is <15, and the pH is usually <8.5.

saline-sodic soil

(1) A soil containing appreciable quantities of soluble salts with enough exchangeable sodium to interfere with the growth of most crop plants as well as an exchangeable sodium percentage >15, a conductivity of a saturation extract >4 dS m-1 at 25°C, and a pH 8.5 or less in the saturated soil. (2) A soil that has a combination of harmful quantities of salts and either a high alkalinity or high content of exchangeable sodium, or both, so distributed in the profile that the growth of most crop plants is reduced.


The amount of dissolved salts in a medium. Soil salinity is the amount of soluble salts in a soil; usually determined by measuring the electrical conductivity of a saturation extract.


The process by which water-soluble salts accumulate in the soil. Salinization may occur naturally or because of conditions resulting from management practices, and is of concern because excess salts hinder the growth of crops by limiting their ability to take up water.


(1) a soil particle between 0.05 and 2.0 mm in diameter; (2) a soil texture class.


Any organism that derives its nutrition from dead or decayed organic material, in contrast to a parasitic organism that obtains its nutrition at the expense of a living organism.

saturated water content

The water content of a soil when all the voids between soil particles are filled with water.


A prepared area in which seed is sown. In natural regeneration, the soil or forest floor on which seed falls.


a category in the Canadian, U.S. and other systems of soil classification. It is the basic unit of soil classification, is a subdivision of a soil family, and consists of soils that are alike in all major profile characteristics except the texture of the A horizon.


Any of the oxides and hydroxides of iron and aluminum.


(1) A soil separate consisting of particles between 0.05 and 0.002 mm in equivalent diameter. (2) A soil texture class.


Polished and striated surfaces that occur along planes of weakness resulting from the movement of one mass of soil against another in soils dominated by swelling clays; commonly observed in Vertisols.

sodic soil

(1) A nonsaline soil containing sufficient exchangeable sodium to interfere with the growth of most crop plants. (2) A soil having an exchangeable sodium percentage of 15 or more. Also called non saline alkali soil.


The level of exchangeable sodium and its influence on a soil.

sodium adsorption ratio (SAR)

The relationship of soluble sodium to soluble calcium plus magnesium in water or the soil solution, expressed by the equation:

SAR=[sodium] / [calcium]1/2

where the concentrations of ions, denoted by square brackets, are in millimoles per liter. This relationship can be used to predict the exchangeable sodium fraction of a soil.

soil [health] quality attribute

Properties that reflect or characterize a soil process, or processes that support a specific soil function.

soil amendment

Any material added to soil that [is intended to] enhances plant growth, via the nutrients they contain, or improves the soil condition (e.g., lime, gypsum, compost, animal manures, plant residues, certain industrial wastes, and synthetic soil conditioners).

soil degradation

The general process by which soil gradually declines in quality and is thus made less fit for a specific purpose, such as crop production. See erosion.

soil depleting crops

Crops that, under their usual management, tend to deplete nutrients and organic matter in the soil and permit deterioration of soil structure.

soil fertility

The inherent ability of soil to support crop growth, without human intervention.

soil formation factors

The interrelated natural agencies responsible for the formation of soil. The factors are typically grouped into following five categories: parent material, climate (precipitation, temperature), organisms (flora and fauna), topography (elevation, slope, depth to water table), and time.

soil function

The various roles that soil performs, or the tasks that are placed upon soil, that underpin the concept of soil quality. Soil functions in three main ways: as a medium for plant growth, a regulator or partitioner of water and energy, and an environmental buffer or filter.

soil health

An approach to soil condition analogous to human or community health, by which the condition of a soil's properties and morphology are assessed against some optimum condition (i.e., soil-as-an-organism), or a soil's functions assessed against the goals placed upon them (i.e., soil-as-a-community), or against an optimum functional state. Often soil health is used synonymously with soil quality, except that a soil may have poor inherent soil quality but still have good health.

soil management

The total of all tillage operations; cropping practices; and application of fertilizer, lime, and other treatments to a soil to produce plants and [ideally] improve soil condition. See tillage, soil management.

soil productivity

The capacity of a soil, in its normal environment, to produce a particular plant or sequence of plants under a defined management system; usually expressed in terms of yield.

soil profile

A vertical section of the soil through all its horizons and extending into the parent material.

soil reclamation

Physical reconstruction of soils and terrain on a disturbed site to achieve equivalent land use capability as to what existed before disturbance. (see land reclamation)

soil remediation

Refers to a wide range of strategies that remove, destroy, contain, transform, or reduce availability of soil contaminants to humans and other receptors in the environment.

soil resiliency

The capacity of a soil to recover its qualitative functions and dynamic properties, generally in a relatively short time frame, after some disturbance; an aspect of soil [health]quality.

soil sealing

Separation of the soil from the atmosphere by an impermeable layer(s). The loss of soil resources through coverage by buildings, construction, impermeable or semi-permeable artificial materials (e.g., asphalt, concrete).

soil separates

Mineral particles, less than 2.0 mm in equivalent diameter, ranging between specified size limits. The names and size limits of separates recognized in Canada and the United States are: very coarse sand, 2.0 to 1.0 mm coarse sand, 1.0 to 0.5 mm; medium sand, 0.5 to 0.25 mm; fine sand, 0.25 to 0.10 mm; very fine sand, 0.10 to 0.05 mm; silt, 0.05 to 0.002 mm; and clay, less than 0.002 mm.

soil solution

The aqueous liquid phase of the soil and its solutes, consisting of ions dissociated from the surfaces of the soil particles, and other soluble materials.

soil structure

(pedology) The combination or arrangement of primary soil particles into secondary particles (i.e., aggregates), units, or peds. These peds may be, but usually are not, arranged in the profile in such a manner as to give a distinctive characteristic pattern. Peds are characterized and classified on the basis of size, shape, and grade (i.e., degree of distinctness) into classes, types, and grades. The arrangement of soil aggregates in cultivated soils as modified by agricultural or human activity, mainly classified on the basis of size rather than shape. Generally classified by soil structural form, soil structural stability, and soil structural resiliency.

soil texture

Units of classification used to express the relative proportions of sand, silt, and clay in a soil.

soil water potential

The potential energy of a unit quantity of water produced by the interaction of the water with forces such as capillary (e.e., matric potential), ion hydration (i.e., osmotic potential), and gravity, expressed relative to an arbitrarily selected reference potential. The total potential of soil water consists of the sum of gravitational potential (hg) + matric potential (hm) + osmotic potential (ho) + pressure potential (hp).

soil water tension

Equal in magnitude but opposite in sign to the soil matric potential. Occurs in soils partially saturated with water.

soil-forming processes

A series of specific changes that lead to soil formation (genesis). Soil forming processes are grouped into four broad categories: additions, losses, transformations and translocations.


Leaching of sodium salts from a horizon.


An order of soils in the Canadian system of soil classification characterized by high sodium levels in the B horizon; usually associated with a clay-rich B horizon and often with saline C horizon material.


Accumulation of sodium salts in a horizon.


The upper horizons of a soil in which the parent material has been modified and in which most plant roots are contained. It usually consists of A and B horizons. (plural sola)


The removal of an ion or molecule from solution by absorption and/or adsorption.

spatial resolution

The dimensions of each raster cell with respect to the area that it is representing on the ground.


A species that has a very selective feeding niche (e.g., that a nematode that only grazes on fungal hyphae).


(ecology) A group of organisms that may interbreed and produce fertile offspring having similar structure, habits, and functions. Species ranks next below genus, as a fundamental unit in the hierarchy of classification. The name of the species becomes the second word of binomial nomenclature systems. Abbreviated as sp. (singular) and spp. (plural). As described in Chapter 6, the "species concept" is challenging to apply for many microorganisms, particularly the bacteria and archaea.

specific surface area (SSA)

The solid-phase surface area (of a soil or porous medium) divided by the solid-particle mass (expressed in m2 g-1), of by the soil-particle volume.


Quantitative relation between the number of moles (and therefore mass) of various products and reactants in a chemical reaction.

strip tillage (partial-width tillage)

Tillage operations performed in isolated bands, separated by bands of soil essentially undisturbed by the particular tillage equipment.


Any treatment to loosen soil with narrow tools below the depth of normal tillage without inversion, and with minimum mixing of the soil. This loosening is usually performed by a lifting action or other displacement of soil dry enough so that shattering occurs.


A substance added to liquid to increase its spreading or wetting properties by reducing its surface tension (e.g., detergents).

sustainable soil management

Management regimes applied to soil that maintain the productive and renewal capacities as well as the genetic, species, and ecological diversity of soil ecosystems.

swelling clay

A clay that is prone to large volume changes that are directly related to changes in water content. Soils with a high content of expansive minerals can form deep cracks in drier seasons or years; such soils are called vertisols. Montmorillonites expand considerably more than other clays due to the adsorption of water in the interlayer molecular spaces. The amount of expansion depends largely on the exchangeable cation present on the exchange complex. The presence of sodium as the predominant exchangeable cation can result in the clay swelling to several times its original volume.


An interaction between two different organisms living in close physical association. Interactions may be mutualistic, commensal, or parasitic.


A group of silicate minerals, such as quartz or feldspar, having a structure in which the SiO4 tetrahedra share all four oxygen atoms with neighboring tetrahedra to form a three-dimensional network with a Si:O ratio of 1:2.

tertiary consumers

Species that feed upon microbial grazers and plant-pests. They can be fully carnivorous or omnivorous (feeding on combinations of fungi, soil animals and living roots and other plant parts).

tetrahedron (tetrahedra, pl.)

A three-dimensional figure having four triangular sides. It may be visualized as a pyramid with a triangular base. The tetrahedral arrangement can be represented by three balls placed in a triangle in contact with each other and a fourth ball resting on top above the center of the triangle. The normal spacing of the oxygen ions in tetrahedra and other compact structures is the same as the diameter of an oxygen ion, about 0.28 nanometers. The space inside an oxygen tetrahedron is so small that only a very small cation, such as Si4+ or Al3+, can fit inside. Even Al3+ is crowded inside oxygen tetrahedra, and is more frequently found in octahedral spaces.

texture (soil)

The relative proportions of the various soil separates (i.e., sand, silt and clay size fractions) in a soil as described by the classes of soil texture. The names of textural soil classes may be modified by adding suitable adjectives when coarse fragments are present in substantial amounts (e.g., stony sandy loam; silt loam, stony phase). Sand, loamy sand, and sandy loam are further subdivided on the basis of the proportions of the various sand separates present.

thermal conductivity

The rate of transfer of heat to or from a point in the soil under unit thermal gradient. Describes heat flow in response to a temperature gradient, expressed in units of J -1 s-1 °C.

thermal treatments

Remediation strategies that make use of heat to separate contaminants from contaminated soil, destroy organic contaminants, and/or melt and then solidify the contaminated soil, thereby immobilizing contaminants and reducing their availability to potential receptors.


Geology:  Unstratified glacial drift deposited directly by the ice and consisting of clay, sand, gravel, and boulders intermingled in any proportion.

Soil management:  To plow or cultivate the soil to control weeds or prepare a seedbed.


The mechanical manipulation of the soil profile for any purpose. In agriculture it is usually restricted to modifying soil conditions and/or managing crop residues and/or weeds and/or incorporating chemicals for crop production.

top-down processes

Trophic interactions in a community, where the levels of the predator determine that of the prey.


(1) The configuration of a surface area including its relief, or relative elevations, and the position of its natural and manmade features. (2) The study or description of the physical features of the Earth's surface. (3) The physical features of a district or region, such as represented on maps, taken collectively; especially the relief and contour of the land.


An octahedral sheet or a mineral containing such a sheet that has all of the sites filled, usually by divalent ions such as magnesium or ferrous iron.

trophic interactions

Processes of energy and nutrient transfer from one or more organisms to others in an ecosystem.


A Newfoundland term for coastal evergreen trees that are deformed by strong ocean winds. Growth can be almost sideways, and roots are gnarled as they spread across the barren land.


Mixing of soil or sediment.


Sowing a secondary crop [or cover crop] with the main crop to provide soil cover after the primary crop is harvested.

unit cell

The smallest number of atoms used to represent the chemical formula of a substance that included the overall symmetry of a crystal of that substance, and from which the entire lattice can be built up by repetition in three dimensions. Typically 2X the formula unit. See also formula unit.

vadose zone

The aerated region of the soil above the permanent water table.

vertic horizon

A diagnostic horizon (Canadian system of soil classification) affected by argillipedoturbation, as manifested by disruption and mixing caused by shrinking and swelling of the soil mass. It is characterized by irregularly shaped, randomly oriented intrusions of displaced materials within the solum, and by vertical cracks, often containing sloughed-in surface materials.


An order of soils in the Canadian system of soil classification found on parent materials high in clay (i.e., greater than 60 % clay) throughout the Prairie Ecozone and also have a very limited extent in other regions of Canada. Characterized by shrinking and swelling of clays and the presence of slickenslides.


Space in a soil mass not occupied by solid matter. This space may be occupied by gaseous or liquid material.

volumetric water content (θv)

The soil-water content expressed as the volume of water per unit bulk volume of soil.

von Post decomposition scale

A scale describing peat in varying stages of decomposition, ranging from H1, which is unconverted, to H10, which is completely decomposed.

1-Undecomposed; plant structure unaltered; yields only clear water colored light yellow-brown.
2-Almost undecomposed; plant structure distinct; yields only clear water colored light yellow-brown.
3-Very weakly decomposed; plant structure distinct; yields distinctly turbid brown water, no peat substance passes between the fingers, residue not mushy.
4-Weakly decomposed; plant structure distinct; yields strongly turbid water, no peat substance escapes between the fingers, residue rather mushy.
5-Moderately decomposed; plant structure clear but becoming indistinct; yields much turbid brown water, some peat escapes between the fingers, residue very mushy.
6-Strongly decomposed; plant structure somewhat indistinct but clearer in the squeezed residue than in the undisturbed peat; about one-third of the peat escapes between the fingers, residue strongly mushy.
7-Strongly decomposed; plant structure indistinct but recognizable; about half the peat escapes between the fingers.
8-Very strongly decomposed; plant structure very indistinct; about two-thirds of the peat escapes between the fingers, residue almost entirely resistant remnants such as root fibers and wood.
9-Almost completely decomposed; plant structure almost unrecognizable; nearly all the peat escapes between the fingers.
10-Completely decomposed; plant structure unrecognizable; all the peat escapes between the fingers.

water content (θ)

The amount of water lost from the soil when it is dried to constant weight at 105°C; expressed either as the weight of water per unit weight of dry soil or as the volume of water per unit bulk volume of soil. The relationship between water content and soil water pressure is called the soil water retention curve.

water table

The upper surface of groundwater or that level below which the soil is saturated.


(geology) The complex combination of physical, chemical, and organic processes that decompose, disintegrate, and alter rocks and minerals at or near the Earth's surface. Weathering can be subdivided into chemical weathering, mechanical or physical weathering, and organic weathering.

Western Cordillera

A mountain chain (or cordillera) extending for a distance of over 6,000 km along the western side of North America, from Mexico to Alaska. Also known as the North American Cordillera or Pacific Cordillera, the Western Cordillera includes parts of Alberta and the Northwest Territories, including the Rocky and Coast Mountains.

Wisconsin glaciation

The most recent glacial episode affecting North America. Also referred to as the Wisconsin Stage or Wisconsin Glacial Episode, it began approximately 75,000 years ago and ended approximately 11,000 years before present.

zero point of charge

The pH at which the net charge of total particle surface is equal to zero.


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Digging into Canadian Soils by Canadian Society of Soil Science is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License, except where otherwise noted.

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