Glossary of Terms in Soil Science

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z #

C horizon

See: horizon; soil

calcareous soil

Soil containing sufficient calcium carbonate often with magnesium carbonate to effervesce visibly when treated with cold 0.1 N hydrochloric acid.


Plants that require or tolerate rather large amounts of calcium or are associated with soils rich in calcium.


(1) A layer near the surface, more or less cemented by secondary carbonates of calcium or magnesium precipitated from the soil solution. It may be a soft thin soil horizon or a hard thick bed just beneath the solum or a surface layer exposed by erosion. It is not a geologic deposit. (2) Alluvium cemented with sodium nitrate or sodium chloride or other soluble salts in the nitrate deposits of Chile and Peru.

capability class

A rating that indicates the capability of land for some use such as agriculture, forestry, recreation, or wildlife. In the Canadian system, it is a grouping of lands that have the same relative degree of limitation or hazard. The degree of limitation or hazard is nil in Class 1 and becomes progressively greater to Class 7.

capability subclass

A grouping of lands that have similar kinds of limitations and hazards. It provides information on the kind of conservation problem or limitation. The class and subclass together provide information about the degree and kind of limitation, for broad landuse planning and for the assessment of conservation needs.

capillary conductivity

(Obsolete) See water: soil: hydraulic conductivity.

capillary fringe

A zone of essentially saturated soil just above the water table. The size distribution of the pores determines the extent and degree of the capillary fringe.

capillary porosity

(Obsolete) The small pores or the bulk volume of small pores that hold water in soils against a tension usually greater than 60 cm (24 inches) of water. See also moisture tension, soil.

capillary potential

See water: soil: matric potential (capillary potential).

capillary water (Obsolete)

The water held in the small pores of a soil, usually with a tension greater than 60 cm (24 inches) of water. See also moisture tension / soil.

carbon cycle

The cycle whereby carbon dioxide is fixed in living organisms by photosynthesis or by chemosynthesis, is consumed in carbohydrate, protein and fat by most animals and plants that do not carry out photosynthesis and ultimately is returned to its original state when it is freed by respiration and by the death and decay of plant and animal bodies.

carbon-nitrogen ratio

The ratio of the weight of organic carbon to the weight of total nitrogen in a soil or in an organic material. It is obtained by dividing the percentage of organic carbon (C) by the percentage of total nitrogen (N).


A grouping of related soils defined at approximately the same level of abstraction. In the Canadian classification the categories are order, great group, subgroup, family and series.


A nontaxonomic grouping of a sequence of soils of about the same age, derived from similar parent materials and occurring under similar climatic conditions but having unlike characteristics because of variations in relief and in drainage.

cation exchange

The interchange of a cation in solution and another cation on the surface of any surface-active material such as clay colloid or organic colloid.

cation exchange capacity

The total amount of exchangeable cations that a soil can adsorb. It is sometimes called ""total exchange capacity"" ""base exchange capacity,"" or ""cation adsorption capacity."" It is expressed in milliequivalents per 100 g of soil or of other adsorbing materials such as clay. See also effective cation exchange capacity and pH-dependent cation exchange capacity.


Having a hard, brittle consistence because the particles are held together by cementing substances such as humus, calcium carbonate or the oxides of silicon, iron and aluminum. The hardness and brittleness persist even when the soil is wet. See also indurated layer


A descriptive term used for thin and flat limestone, sandstone or schist fragments up to 15 cm (6 inches) in length. See also coarse fragments.

check-basin irrigation

See irrigation methods.

chemistry (soil)

The division of soil science dealing with the chemical constitution, properties and reactions of soils.


An order of soils that have developed under xerophytic or mesophytic grasses and forbs or under grassland-forest transition vegetation in cool to cold subarid to subhumid climates. The soils have a dark-colored surface (Ah or Ahe or Ap) horizon and a B or C horizon or both of high base saturation. See also Chernozemic Soil Classification.

chisel / subsoil

See subsoiling.


A tillage implement having one or more cultivator-type feet to which are attached strong knifelike tools that are used to shatter or loosen hard compact layers usually in the subsoil to depths below normal plow depth. See also subsoiling.


A nitrogen-containing polysaccharide present in the covering layer of insects and in the cell walls of many fungi.

chlorite group

A group of nonexpanding platy clay minerals similar chemically to the vermiculite group but having a single hydroxide layer between the sheets in place of the exchangeable cations and water.


The relative purity, strength or saturation of a color. It is directly related to the dominance of the determining wavelength of light. It is one of the three variables of color. See also Munsell color system; hue; value; color.


A sequence of related soils that differ from one another in certain properties primarily as a result of time as a soil-forming factor.

class (soil)

A group of soils having a definite range in a particular property such as acidity, degree of slope, texture, structure, land-use capability, degree of erosion, or drainage. See also structure, soil and texture, soil.

classification / soil

The systematic arrangement of soils into categories on the basis of their characteristics. Broad groupings are made on the basis of general characteristics and subdivisions on the basis of more detailed differences in specific properties. See: The Canadian System of Soil Classification.


(1) As a particle-size term: a size fraction less than 0.002 mm in equivalent diameter, or some other limit (geologists and engineers). (2) As a rock term: a natural, earthy, fine grained material that develops plasticity with a small amount of water. (3) As a soil term: a textural class. See also texture, soil.. (4) As a soil separate: a material usually consisting largely of clay minerals but commonly also of amorphous free oxides and primary minerals.

clay films (skins)

Coatings of oriented clays on the surfaces of soil peds and mineral grains and in soil pores.

clay loam

Soil material that contains 27% to 40% clay and 20% to 45% sand. See also texture, soil.

clay mineral

Finely crystalline hydrous aluminum silicates and hydrous magnesium silicates with a phyllosilicate structure.


Containing large amounts of clay or having properties similar to those of clay.


A term used in the United States for a dense, compact layer in the profile having a much higher clay content than the overlying material, from which it is separated by a sharply defined boundary. In the Canadian classification system, this pan is recognized as a clay-enriched illuvial B (Bt) horizon.

climatic index

A simple, single numerical value that expresses climatic relationships; for example, the numerical value obtained in Transeau's precipitation-evaporation ratio.


A plant community of the most advanced type capable of development under, and in dynamic equilibrium with, the prevailing environment.


A sequence of related soils that differ from one another in certain properties primarily as a result of the effect of climate as a soil-forming factor.


A group of related soils that differ from one another in certain properties primarily as a result of the effect of the degree of slope on which they were formed. See also toposequence.


A compact, coherent mass of soil produced by digging or plowing. Clods usually slake easily with repeated wetting and drying.

coarse fragments

Rock or mineral particles greater than 2.0 mm in diameter. The names used for coarse fragments in soils are shown in Table 2.

coarse sand

See separates; soil and texture; soil.

coarse sandy loam

See texture, soil.

coarse texture

The texture exhibited by sands, loamy sands, and sandy loams except very fine sandy loam. A soil containing large quantities of these textural classes. See also sand, sandy and moderately coarse texture.


Material covering the soil particles. See also clay films (skins).


See cobblestone.


Rounded or partially rounded rock or mineral fragment 7.5 to 25 cm (3 to 10 inches) in diameter. In engineering practice, cobbles are greater than 7.5 cm (3 inches) but less than 20 cm (8 inches) in diameter. See also coarse fragments


Containing appreciable quantities of cobblestones. The term is used to describe both soil and land. ""Angular cobbly"" is used when the fragments are less rounded. See also coarse fragments.


A substance in a state of fine subdivision, whose particles are 10-4 to 10-7 cm in diameter.


A heterogeneous mixture of material that as a result of gravitational action has moved down a slope and settled at its base. See also creep.


A macroscopically visible growth of microorganisms on a solid culture medium.


See Munsell color system.


See structure types, soil.


A relationship between two kinds of organisms living in the same cultural environment without harm to either species and in which one or both members of the pair may obtain food, protection, or other benefits.

compact soil

See consistence.

complex (soil)

A mapping unit used in detailed and reconnaissance soil surveys where two or more defined soil units are so intimately intermixed geographically that it is impractical because of the scale used to separate them.


Organic residues, or a mixture of organic residues and soil that have been piled, moistened and allowed to decompose. Mineral fertilizers are sometimes added. If it is produced mainly from plant residue it is often called ""artificial manure"" or ""synthetic manure.""


The susceptibility of a soil to decrease in volume when subjected to load.

concentrated flow

The flowing of a rather large accumulated body of water over a relatively narrow course. It often causes serious erosion and gullying.

concrete frost

Ice in the soil in such quantity as to form virtually a solid block.


A mass or concentration of a chemical compound such as calcium carbonate or iron oxide in the form of a grain or nodule of varying size, shape, hardness and color found in soil and in rock. The term is sometimes restricted to concentrations having concentric fabric. The composition of some concretions is unlike that of the surrounding material.

conservation (soil)

(1) Protection of the soil against physical loss by erosion or against chemical deterioration; that is, excessive loss of fertility by either natural or artificial means. (2) A combination of all methods of management and land use that safeguard the soil against depletion or deterioration by natural or man-induced factors. (3) The division of soil science dealing with soil conservation 1. and 2. above.


  1. The resistance of a material to deformation or rupture.
  2. The degree of cohesion or adhesion of the soil mass.

Terms used for describing consistence at various soil moisture contents are:

wet soil:

nonsticky, slightly sticky, sticky, and very sticky; nonplastic, slightly plastic, plastic, and very plastic.

moist soil:

loose, very friable, friable, firm, and very firm; compact, very compact, and extremely compact.

dry soil:

loose, soft, slightly hard, hard, very hard, and extremely hard.


weakly cemented, strongly cemented, and indurated.

In engineering practice, "consistency" has essentially the same meaning as "consistence."


The gradual reduction in volume of a soil mass resulting from an increase in compressive stress.

constitutive enzyme

An enzyme whose formation does not depend on the presence of a specific substrate

control section (soil)

The vertical section upon which the taxonomic classification of soil is based. The control section usually extends to a depth of 100 cm (40 inches) in mineral materials and to 160 cm (64 inches) in organic materials.

coprogenous earth

A material in some organic soils that contains at least 50% by volume of fecal pellets less than 0.5 mm in diameter.


Fecal pellet, casting

corrected lime potential

Defined as pH - 1/2p(Ca + Mg) - 1/3(pKg - pY) where Kg is the solubility product of gibbsite and Y is the value of the ionic product (Al)(OH)3 in the soil solution. The corrected lime potential (CLP) is also equal to 1/6 log [(Ca + Mg)(OH)2]3/[(Al)(OH)3]2 + KCLP where KCLP is a constant dependent on temperature only. The CLP is therefore the ratio of the cube of the sum of the activities of Ca and Mg hydroxide to the square of the activity of Al hydroxide in the soil solution. The CLP has a relationship to the degree of base saturation based on the effective cation exchange capacity but the pH and the lime potential do not. See also lime potential.

corrugation irrigation

See irrigation methods

cradle knoll

A small knoll formed by earth that was raised and left by an uprooted tree. See also microrelief

crag and tail

An elongate hill that has at one end a steep face of ice-smoothed rock and at the leeward end a tapering streamlined tail of till.


Slow mass movement of soil and soil material down rather steep slopes primarily under the influence of gravity, but aided by saturation with water and by alternate freezing and thawing. In engineering usage creep is any general slow displacement under load.

crevasse fillings

Ridges or hummocks formed from glacial sediments that were deposited by water in the cracks and crevasses of the ice.

critical density

The unit weight of a saturated granular material below which it will lose strength and above which it will gain strength when subjected to rapid deformation. The critical density of a given material depends on many factors.

critical void ratio

The void ratio corresponding to the critical density.


An arrangement in which thin layers of stratified sediment are transverse or oblique to the main plane of stratification.


A former animal burrow in one soil horizon that has become filled with organic matter or material from another horizon. It is also spelled ""krotovina.""

crushing strength

The force required to crush a mass of dry soil, or conversely, the resistance of a mass of dry soil to crushing. It is expressed in units of force per unit area (pressure).


A surface layer of soil from a few millimetres to 2.5 cm (1 inch) thick that when dry is much more compact, hard and brittle than the material just under it.

cryic layer

A perennially frozen layer.


The study of the properties of snow, ice and frozen ground.


An order of soils proposed for adoption in the Canadian taxonomic system. Cryosolic soils are mineral or organic soils that have perennially frozen material within 1 m (3 ft) of the surface in some part of the soil body, or pedon. The mean annual soil temperature is less than 0øC (32øF). They are the dominant soils of the zone of continuous permafrost and become less widespread to the south in the zone of discontinuous permafrost; their maximum development occurs in organic and poorly drained, fine textured materials. The vegetation associated with Cryosolic soils varies from sparse plant cover in the high arctic, through tundra, to subarctic and northern boreal forests. The active layer of these soils is frequently saturated with water, especially near the frozen layers, and colors associated with gleying are therefore common in mineral soils, even those that occur on well drained portions of the landscape. They may or may not be markedly affected by cryoturbation. The order has three great groups: Turbic Cryosol, comprising mineral soils that display marked cryoturbation and generally occur on patterned ground; Static Cryosol, mineral soils without marked cryoturbation; and Organo Cryosol, organic soils.


Frost action including frost heaving.


A homogeneous inorganic substance of definite chemical composition bounded by plane surfaces that form definite angles with each other to give the substance a regular geometrical form. See also mineral, soil.

crystal lattice

See lattice structure.


A hill or ridge that has a steep cliff on one side and a more gradual slope on the other side controlled more or less by the attitude of the rock strata.


Tillage to prepare land for seeding or transplanting and later to control weeds and loosen the soil.

cumulo layer

A layer of sandy, silty, or clayey material in an Organic soil.


A modification of the texture, structure or fabric at natural surfaces in soil materials due to concentration of particular soil constituents or in situ modification of the matrix. Cutans may be composed of any of the component substances of the soil material.