Glossary of Terms in Soil Science

saline alkali soil

(1) A soil containing enough exchangeable sodium to interfere with the growth of most crop plants, and containing appreciable quantities of soluble salts. The exchangeable-sodium percentage is greater than 15, the conductivity of the saturation extract is greater than 4 mmhos/cm at 25øC, and the pH is usually 8.5 or less in the saturated soil. (2) A saline-alkali soil 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. It is also called saline-sodic soil.

saline soil

A nonalkali soil that contains enough soluble salts to interfere with the growth of most crop plants. The conductivity of the saturation extract is greater than 4 mmhos/cm, the exchangeable-sodium percentage is less than 15, and the pH is usually less than 8.5.

salinity soil

The amount of soluble salts in a soil, expressed in terms of percentage, parts per million or other convenient ratios.


The process of accumulation of salts in soil.

salt-affected soil

Soil that has been adversely modified for the growth of most crop plants by the presence of certain types of exchangeable ions or of soluble salts. It includes soils having an excess of salts, or an excess of exchangeable sodium or both. See also saline-alkali soil, saline soil and sodic soil.


A soil particle between 0.05 and 2.0 mm in diameter. Any one of five soil separates: very coarse sand, coarse sand, medium sand, fine sand or very fine sand. See also separates / soil. A soil textural class. See also texture, soil.


Containing a large amount of sand. It may be applied to any one of the soil classes that contains a large percentage of sand. See also class, soil and texture, soil.

sandy clay

A soil textural class. See also class, soil and texture, soil.

sandy clay loam

A soil textural class. See also class, soil and texture, soil.

sandy loam

A soil textural class. See also class, soil and texture, soil.


(1) To fill all the voids between soil particles with a liquid. (2) To form the most concentrated solution possible under a given set of physical conditions in the presence of an excess of the solute. (3) To fill to capacity, as the adsorption complex with a cation species; for example, H-saturated .

saturation extract

The extract from a soil sample that has been saturated with water.

science; soil

The science dealing with soil as a natural resource. It includes: soil formation, classification and mapping; the physical, chemical and biological properties of soils and the management of soils for various purposes such as the production of agricultural and forest crops, the construction of roads and others.

second bottom

The first terrace above the normal flood plain of a stream.

secondary mineral

A mineral resulting from the decomposition of a primary mineral or from the precipitation of the products of decomposition of a primary mineral. See also primary mineral.

sedimentary rock

A rock formed from materials deposited from suspension or precipitated from solution and usually more or less consolidated. The principal sedimentary rocks are sandstones, shales, limestones and conglomerates.


(1) The escape of water downward through the soil. (2) The emergence of water from the soil along an extensive line of surface in contrast to a spring where the water emerges from a local spot.

self-mulching soil

A soil in which the surface layer becomes so well aggregated that it does not crust and seal under the impact of rain but instead serves as a surface mulch when it dries.


The effect of remolding on the shear strength of an undrained cohesive soil.

separates (soil)

Mineral particles, less than 2.0 mm in equivalent diameter, ranging between specified size limits. The names and size limits of separates recognized by pedologists in Canada and the United States are: (1) very coarse sand, 2.0 to 1.0 mm; (2) coarse sand, 1.0 to 0.5 mm; (3) medium sand, 0.5 to 0.25 mm; (4) fine sand, 0.25 to 0.10 mm; (5) very fine sand, 0.10 to 0.05 mm; (6) silt,0.05 to 0.002 mm; (7) clay, less than 0.002 mm; and (8) fine clay, less than 0.0002 mm. The separates recognized by the International Society of Soil Science are: (1) coarse sand, 2.0 to 0.2 mm; (2) fine sand, 0.2 to 0.02 mm; (3) silt, 0.02 to 0.002 mm; and (4) clay, less than 0.002 mm.


A sequence of an eluvial horizon and its related illuvial horizon in a soil.

serial dilution

Successive dilution of a specimen, for example, 1:10 dilution equals 1 ml of a specimen plus 9 ml of diluent (e.g., sterile water); 1:100 dilution equals 1 ml of a 1:10 dilution plus 9 ml of diluent.

series (soil)

A category in the Canadian system of soil classification. This is the basic unit of soil classification and consists of soils that are essentially alike in all major profile characteristics except the texture of the surface.


(1) Containing a large amount of shale fragments. (2) A soil phase; for example shaly phase. (3) Kind of fragment see coarse fragments.

shear stress

The force per unit area acting tangentially to a given plane within a soil mass.

sheet erosion

The removal of a fairly uniform layer of soil from the land surface by runoff water.

sheet erosion

See erosion (2.).

silica-alumina ratio

The molecules of silicon dioxide (SiO2) per molecule of aluminum oxide (Al203) in clay minerals or soils.

silica-sesquioxide ratio

The molecules of silicon dioxide (SiO2) per molecule of aluminum oxide (Al203) plus ferric oxide (Fe203) in clay minerals or soils.


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

silt loam

A soil textural class. See also texture, soil and class, soil.


The deposition of water-borne sediments in stream channels, lakes, reservoirs or on floodplains usually resulting from a decrease in the velocity of the water.


A very fine grained, consolidated. clastic rock composed predominantly of particles of silt grade.

silty clay

A soil textural class. See also texture / soil and class / soil.

silty clay loam

A soil textural class. See also texture, soil and class, soil.

single-grain structure

A soil structure in which the soil particles occur almost completely as individual or primary particles; secondary particles or aggregates are seldom present. It is usually found only in extremely coarse-textured soils.


(1) In ecology, an area described or defined by its biotic, climatic, and soil conditions in relation to its capacity to produce vegetation. (2) An area sufficiently uniform in biotic, climatic and soil conditions to produce a particular vegetation.

site index

(1) A quantitative evaluation of the productivity of a soil for forest growth under the existing or specified environment. (2) The height in feet of the dominant forest vegetation taken at or calculated to an index age usually 50 or 100 years.

sixty-centimetre tension

See moisture tension, soil.


Rock and mineral particles larger than two mm occupy 35% or more but less than 90% (by volume)

slaking (soil)

The breakdown of aggregates resulting from the addition of water to soil.


Containing a considerable quantity of slate fragments. It is used to modify soil texture class names such as slaty clay loam. See also coarse fragments.

slick spots

Small areas in a field that are slick when wet, because of a high content of alkali or exchangeable sodium.


Fine-textured materials separated in placer mining and in ore-mill operations; the materials may be detrimental to plant growth and so should be confined in specially constructed basins. A miscellaneous land type.


Smoothed surfaces along planes of weakness resulting from the movement of one mass of soil against another in soils dominated by swelling clays.


See montmorillonite group.

sodic soil

(1) A soil containing sufficient sodium to interfere with the growth of most crop plants. (2) A soil having an exchangeable-sodium percentage of 15 or more.

soil (1)

(1) The unconsolidated material on the immediate surface of the earth that serves as a natural medium for the growth of land plants.

soil (2)

(2) The naturally occurring unconsolidated material on the surface of the earth that has been influenced by parent material, climate (including the effects of moisture and temperature), macro- and micro-organisms and relief all acting over a period of time to produce soil that may differ from the material from which it was derived in many physical, chemical, mineralogical, biological and morphological properties.

soil (3)

(3) For the purpose of the Canadian taxonomic system, the earth's surface (the material that is to be classified) is divided into soil and nonsoil. Soil is the naturally occurring unconsolidated mineral or organic material at the earth's surface that is capable of supporting plant growth. It extends from the surface to 15 cm (6 inches) below the depth at which properties produced by soil-forming processes can be detected. These properties differ from those found in any underlying unconsolidated material. The soil-forming processes are defined as an interaction between climate, living organisms and relief acting on soil and soil parent material. Unconsolidated material includes material cemented or compacted by soil-forming processes. Soil may have water covering its surface to a depth of 60 cm (24 inches) or less in the driest part of the year. See also nonsoil.

soil moisture tension

In soils partially saturated with water there is moisture tension, which is equal in magnitude but opposite in sign to the soil water pressure. Moisture tension is equal to the pressure that must be applied to the soil water to bring it to a hydraulic equilibrium through a porous permeable wall or membrane with a pool of water of the same composition. See also water / soil The pressures used and the corresponding percentages most commonly determined are: - 15-atmosphere percentage, - 15-bar percentage, - 1/3-atmosphere percentage, - 1/3-bar percentage, - 60-centimetre percentage.

soil-formation factors

The variable, usually interrelated natural agencies that are responsible for the formation of soil. The factors are: parent rock, climate, organisms, relief, and time.


The temperature and moisture conditions of the soil; the soil climate.


A type of creep that takes place in regions where the ground freezes to a considerable depth and as it thaws during the warm seasons the upper thawed position creeps downhill over the frozen material. The soil moves as a viscous liquid down slopes of as little as 2 or 3 degrees and may carry rocks of considerable size in suspension.


A great group of soils in the Solonetzic order occurring most commonly in the grassland and parkland regions. The soils have a dark-colored surface (Ah) horizon; a prominent eluvial (Ahe or Ae) horizon at least 5 cm (2 inches) thick, a prominent transitional (AB) horizon that breaks readily into blocky aggregates and a darkly stained B (Bnt) horizon over a C horizon that is saline and usually calcareous.

solodized soil

A soil that has been subjected to the processes responsible for the development of a Solod and has at least some of the characteristics of a Solod.

Solodized Solonetz

A great group of soils in the Solonetzic order, occurring most commonly in the grassland and parkland regions and consisting of soils with a variable surface (Ah, Ahe, or Ae) horizon that is underlain by a well-developed Ae horizon, a compact prismatic or columnar Bnt horizon, and a C horizon that is saline and usually calcareous.


A great group of soils in the Solonetzic order, occurring most commonly in the grassland and parkland regions and consisting of soils with a variable surface (Ah, Ahe, or Ae) horizon that breaks abruptly into a hard, compact prismatic or columnar B (Bnt, rarely a Bn) horizon underlain by one or more saline and usually calcareous (Bs, Cs, Csa, Csk, Cca) horizons. They lack a continuous Ae horizon 2.5 cm (1 inch) or more thick.


An order of soils developed mainly under grass or grass-forest vegetative cover in semiarid to subhumid climates. The soils have a stained brownish solonetzic B (Bnt or Bn) horizon and a saline C horizon. The surface may be one or more of Ap, Ah or Ae horizons. See also: Solonetzic Soil Classification.

soluble-sodium percentage (SSP)

The proportion of sodium ions in solution in relation to the total cation concentration, defined as follows: SSP = [soluble sodium concentration (meq/litre) / total cation concentration (meq/litre)] x 100

solum (plural sola)

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.

solution; soil

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

Sombric Brunisol

A great group of soils in the Brunisolic order. The soils have moder Ah horizons more than 5 cm (2 inches) thick and Bm horizons in which the base saturation (NaCl) is usually 65% to 100% and the pH (CaCl2) is usually about 5.5.

splash erosion

The spattering of small soil particles caused by the impact of raindrops on very wet soils. The loosened and spattered particles may or may not be subsequently removed by surface runoff.

splash erosion

See erosion (2.).

spoil bank

Rock waste, banks, and dumps, from the excavation of ditches.

sprinkler irrigation

See irrigation methods.

stabilization (soil)

Chemical or mechanical treatment designed to increase or maintain the stability of a mass of soil or otherwise to improve its engineering properties.


The process of making sterile, the killing of all forms of life.

sticky point

(1) A condition of consistence at which the soil barely fails to stick to a foreign object. (2) Specificaliy and numerically, the weight moisture percentage of a well-mixed, kneaded soil that barely fails to adhere to a polished nickel or stainless steel surface when the shearing speed is 5 cm/sec. The measurement is made rarely now.

Stokes law

An equation relating the terminal settling velocity of a smooth, rigid sphere in a viscous fluid of known density and viscosity to the diameter of the sphere when subjected to a known force field. It is used in the particle-size analysis of soils by the pipette, hydrometer, or centrifuge methods. The equation is: V = (2gr²)(d1-d2)/9µ where V = velocity of fall (cm sec-¹), g = acceleration of gravity (cm sec-²), r = ""equivalent"" radius of particle (cm), dl = density of particle (g cm -³), d2 = density of medium (g cm-³), and µ = viscosity of medium (dyne sec cm-²).


Rock fragments greater than 25 cm (10 inches) in diameter if rounded and greater than 38 cm (15 inches) along the greater axis if flat. See also coarse fragments. In engineering practice these fragments are included with boulders, which are considered to be greater than 20 cm (8 inches) in diameter.


The relative proportion of stones in or on the soil. This term is used in the classification of soils. See also coarse fragments.


Containing sufficient stones to interfere with or prevent tillage. To be classified as stony, more than 0.1% of the surface of the soil must be covered with stones. The term is used to modify soil class, as stony clay loam or clay loam, stony phase. See also coarse fragments.

stony land

Areas containing sufficient stones to make the use of machinery impractical; usually 15% to 90% of the surface soil is covered with stones. See also stoniness.


The arrangement of sediments in layers or strata marked by a change in color, texture, dimension of particies and composition. Stratification usually means layers of sediments that separate readily along bedding planes because of different sizes and kinds of material or some interruption in deposition that permitted changes to take place before more material was deposited.

stratified drift (or sorted drift)

Materials that are distinctly sorted according to size and weight of their component fragments indicating a medium of transport (water or wind) more fluid than glacier ice.

stratum (plural strata)

A layer characterized by certain unifying characteristics, properties, or attributes distinguishing it from adjacent layers.


A directional force acting within a material.

strip cropping

The practice of growing crops that require different types of tillage, such as row and sod, in alternate strips along contours or across the prevailing direction of wind.

structure classes (soil)

A grouping of soil structural units or peds on the basis of size. These are tabulated under structure types, soil (Table 3).

structure grades (soil)

A grouping or classification of soil structure on the basis of inter- and intra- aggregate adhesion, cohesion, or stability within the profile. Three grades of structure designated from 1 to 3 are: (1) weak (structure faible): poorly formed, indistinct peds barely evident in place. (2) moderate (structure modérée): well-formed distinct peds, moderately durable and evident but not distinct in undisturbed soil. (3) strong (structure forte): durable peds that are quite evident in undisturbed soil, adhere weakly to one another, withstand displacement and become separated when the soil is disturbed.

structure index

Any measurement of a soil physical property, such as aggregation, porosity, permeability to air or water or bulk density that denotes or indicates the structural condition of a soil.

structure, soil

The combination or arrangement of primary soil particles into secondary particles, 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. The peds are characterized and classified on the basis of size, shape, and degree of distinctness into classes, types, and grades. See also structure classes, soil; structure grades, soil; and structure types, soil. These are defined and tabulated under structure types, soil (Table 3).

stubble mulch

The stubble of crops or crop residues left essentially in place on the land as a surface cover before and during the preparation of the seedbed and at least partly during the growing of a succeeding crop. Synonymous with trash cover.

subgroup, soil

A category in the Canadian classification system. These soils are subdivisions of the great groups and therefore each soil is defined more specifically.


See irrigation methods.


The breaking of compact subsoils, without inverting them, with a special knifelike instrument (chisel), which is pulled through the soil usually at depths of 30 to 60 cm (12 to 24 inches) and spacings of 60 to 150 cm (2 to 5 ft). Also called chiseling.


(1) That which is laid or spread under; an underlying layer, such as the subsoil. (2) The substance, base, or nutrient on which an organism grows. (3) Compounds or substances that are acted upon by enzymes or catalysts and changed to other compounds in the chemical reaction.

subsurface tillage

Tillage with a special sweeplike plow or blade, which is drawn beneath the surface at depths of several centimetres and cuts plant roots and loosens the soil without inverting it or incorporating the surface cover.

sulfofication (Obsolete)

The biological oxidation of sulfur and sulfur compounds in the soil.

summation curve (of particle sizes)

A curve showing the accumulative percentage by weight of particles within increasing or decreasing size limits as a function of diam¿ter; the percentage by weight of each size fraction is plotted accumulatively on the ordinate as a function of the total range of diameters represented in the sample plotted on the abscissa.

surface runoff

See runoff.

surface sealing

The orientation and packing of dispersed soil particles in the immediate surtace layer of the soil to render the surface fairly impermeable to water.

surface soil

The uppermost part of the soil that is ordinarily moved in tillage, or its equivalent in uncultivated soils. It ranges in depth from 7.5 to 25 cm (3 to 10 inches) and is frequently designated as the ""plow layer"" the ""Ap layer"" or the ""Ap horizon.""

survey soil

The systematic examination, description, classification, and mapping of soils in an area. Soil surveys are classified according to the kind and intensity of the field examination.

sustained yield

A continual annual or perlodic yield of plants or plant material from an area; implies management practices that maintain the productive capacity of the land.


An area saturated with water throughout much of the year, but with the surface of the soil usually not deeply submerged, It Is generally characterized by tree or shrub vegetation. See also marsh and miscellaneous land type.


The living together in intimate association of two dissimllar organisms, so that the cohabitation is mutually beneficial.

symmetry concentration

The quantity of cations or anions equivalent to the exchange capacity of a soil, For example, if the cation exchango capacity of a soil is 10 meq/l00 g of soil, then 1 symmetry concontration is 10 meq of any cation.

symmetry value

The percentage of the adsorbed ion released when one symmetry concontration of another ion is added.


The ability of two or more organisms to bring about changes (usually chemical) that neither can accomplish alone.