Glossary of Terms in Soil Science

B horizon

See: horizon; soil

badland

A land type generally devoid of vegetation and brohen by an intricate maze of narrow ravines, sharp crests, and pinnacles resulting from serious erosion of soft geologic materials. This type is most common in arid or semiarid regions. It is a miscellaneous land type.

bar

A unit of pressure equal to one million dynes per square centimetre.

base course; base

A layer of specified or selected material of planned thickness constructed on the subgrade or subbase for distributing load and providing drainage or minimizing frost action and other such purposes.

base saturation percentage

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

beach deposits

Sediments that are modified in their degree of sorting or surface relief or both by the action of waves .

bearing capacity

The average load per unit area that is required to rupture a supporting soil mass.

bed

A unit layer 1 cm (0.4 inch) or more thick that is visually or physically more or less distinctly separable from other layers above and below in a stratified sequence.

bedrock

The solid rock that underlies soil and the regolith or that is exposed at the surface.

bench terrace

See terrace.

biosequence

A sequence of related soils that differ from one another primarily in the kinds and numbers of soil organisms that play a part in soil formation.

bisect

A profile of plants and soil showing the vertical and lateral distribution of roots and tops in their natural position.

bisequa

Two sequa in one soil; that is, two sequences of an eluvial horizon and its related illuvial horizon.

Black

A great group of soils in the Chernozemic order. The soils occur in the cool to cold subhumid grassland and parkland regions. They have a very dark surface (Ah or Ap) horizon and ordinarily a brownish B (Bm, Btj or Bt) horizon which may be absent over a highly base-saturated usually calcareous C horizon.

blocky

See structure types; soil.

blowing sand

Sandy material that is or has been subjected to wind action.

blown out land

An area from which all or almost all the soil and soil material have been removed by wind erosion. It is usually a barren shallow depression that has a flat or irregular floor consisting of a rather resistant layer or an accumulation of pebbles or both or a wet zone immediately above a water table. The land is usually unfit for crop production. It is a miscellaneous land type.

blowout

A small area from which soil material has been removed by wind.

bog

Permanently wet land having low bearing strength.

bog iron

Impure iron deposits that develop in bogs or swamps by the chemical or biochemical oxidation of iron carried in solution.

border-strip irrigation

See irrigation methods.

bottomland

See floodplain.

boulders

Rock fragments over 60 cm (2 ft) in diameter. In engineering practice boulders are greater than 20 cm (8 inches) in diameter. See also coarse fragments.

breccia

A rock composed of coarse angular fragments cemented in a fine-grained matrix.

Brown

A great group of soils in the Chernozemic order. The soils occur in the cool, subarid to semiarid grassland regions, and consist of a brown (dry) surface (Ah or Ap) horizon and ordinarily a lighter-colored brownish B (Bm, Btj or Bt) horizon which may be absent over a highly basesaturated usually calcareous C horizon.

Brunisolic

An order of soils whose horizons are developed sufficiently to exclude the soils from the Regosolic order but that 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. See also: Brunisolic Soil Classification.

buffer compounds/ soil

The clay, organic matter, and materials such as carbonates and phosphates that enable the soil to resist appreciable change in pH.

bulk density; soil

The mass of dry soil per unit bulk volume. The bulk volume is determined before the soil is dried to constant weight at 105° C. It has been called apparent density.

bulk specific gravity

The ratio of the bulk density of a soil to the mass of a unit volume of water. (It is also called apparent specific gravity.)

bulk volume

The volume, including the solids and the pores, of an arbitrary soil mass.

buried soil

Soil covered by an alluvial loessial or other deposit usually to a depth greater than the thickness of the solum.

butte

An isolated hill rising abruptly above the surrounding area and having steep sides and a flat top. Most of the top has been removed by erosion and it has a smaller summit area than a mesa.