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 #

Oil wasteland

Land on which oily wastes have accumulated, including slush pits and adjacent areas affected by oil waste. A miscellaneous land type.

one-third atmosphere percentage

See moisture tension / soil.

one-third bar percentage

See 1/3-atmosphere percentage

order; soil

A category in the Canadian system of soil classification. All the soils of Canada have been divided into ten orders: Chernozemic, Solonetzic, Luvisolic, Podzolic, Brunisolic, Regosolic, Gleysolic, Vertisolic, Cryosolic, and Organic. All the soils within an order have one or more characteristics in common.


An order of soils that have developed dominantly from organic deposits. The majority of Organic soils are saturated for most of the year, unless artificially drained, but some of them are not usually saturated for more than a few days. They contain 17% or more organic carbon, and: (1) if the surface layer consists of fibric organic material and the bulh density is less than 0.1 [with or without a mesic or humic Op less than 15 cm (6 inches) thick], the organic material must extend to a depth of at least 60 cm (24 inches); or (2) if the surface layer consists of organic material with a bulk density of 0.1 or more, the organic material must extend to a depth of at least 40 cm (16 inches); or (3) if a lithic contact occurs at a depth shallower than stated in 1) or 2) above, the organic material must extend to a depth of at least 10 cm (4 inches). See also: Organic Soil Classification.

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 soils that have been sieved through a 2.0-mm sieve.

organic phosphorus

Phosphorus present as a constituent of an organic compound or a group of organic compounds such as glycerophosphoric acid, inositol phosphoric acid and cytidylic acid.


(1) An indurated layer in the B horizon of Podzols in which the cementing material consists of illuviated sesquioxides and organic matter. (2) As a subgroup of Podzolic soils, Ortstein indicates a Bhfc or Bfc horizon that is strongly cemented, occurs over at least one-third of the exposure, and is at least 2.5 cm (1 inch) thick.

osmotic potential

See water/ soil.

Osmotic pressure

See water; soil.


Sediments washed out by flowing water beyond the glacier and laid down as stratified drift in thin foreset beds. The particle size may vary from boulders to silt.

ovendry soil

Soil that has been dried at 105°C until it has reached constant weight.

Overconsolidated soil deposit

A soil deposit that has been subjected to an effective pressure greater than the present overburden pressure.