Soil Science Midterm Vocabulary

Aeration pore

Large (noncapillary) pores that normally drain free of liquid water because of gravitational drainage and fill up with air.

Anchorage

Function of soil to hold plant firmly in place

Best Management Practice (BMP)

A practice recommended to reduce environmental impact of such activities as farming or land development, that is practical for the practitioner. In this text, applied to such land management practices as soil conservation, manure handling, stormwater management, and others.

carbon sequestration

Removal of carbon dioxide form the atmosphere and its deposition in some sink.

carbon sink

A location where, as part of the carbon cycle, carbon is trapped for a time so it does not return to the atmosphere as carbon dioxide

Cropland

Land used for the purpose of raising crops

Desertification

Conversion of land to desert, often caused by overgrazing, deforestation, or other disturbance

Hardpan

layer of hard material just below surface preventing good drainage

Hydroponic crop

Crops grown in nutrient solutions rather than soil.

Load Bearing Capacity

Ability of a soil to carry a load like a roadbed or building without shifting

Macropore

Large spaces between aggregates that become filled with air as water drains

micropore

space between soil particles that is relatively small and likely to be water filled

Nutrient

Elements in the form of ions or molecules used in the metabolism of plants, animals, and microbes

Photosynthesis

The reaction, in the presence of chlorophyll, of carbon dioxide and water to form sugar, using light energy

Pore space

Portion of soil not occupied by solid material but which is filled with water or air

Respiration

Biological reaction in which carbohydrates are broken down to carbon dioxide and water with the release of energy

Shrink-sell potential

How much mass of soil swells when wet and shrinks when dry; a function of the amount of swelling clays

Soil aeration

Air in the soil is replaced by air from the atmosphere

Soil air

Gas phase of soil; space of soil not filled with solid or liquid.

Soil degradation

Loss of soil quality through such processes as erosion, salination, contamination, severe compaction, and numerous others.

Soil matrix

The arrangement of solid particles and pore spaces

Soil quality

Capacity of a soil to provide the needed functions for human or natural ecosystems over the long term.

Soil solution

The liquid phase of soil, consisting of water and dissolved ions.

Waterlogged soil

Soil whose pores are filled with water and so are low in oxygen. Caused by high water tables, poor drainage, or excess moisture from rain, irrigation, or flooding.

Alluvial fan

a fan-shaped alluvial deposit formed by a stream where its velocity is abruptly decreased, as at the mouth of a ravine or at the foot of a mountain.

Alluvial soil

soil that was deposited by running water

Caliche

A calcium carbonate-rich hardpan soil horizon; the extent of caliche formation can be used to determine the age of desert soils

Chemical weathering

the breakdown of rocks and minerals by chemical reactions, mostly water

Colluvium

A deposit of rock and soil resulting from materials sliding down a slope under the force of gravity.

Delta

a fan-shaped area of silt near where a river flows into the sea

Dissolution

Process of a solid passing into solution. (Chemical weathering)

Eluviation

Removal of a material, such as clay or nutrients, from a layer of soil by percolating water.

Eolian deposit

wind-deposited soil material, mostly silt and fine sand

Floodplain

land near a river that is likely to be under water during a flood

Frost wedging

Breakage of rocks caused by pressure created by water freezing in cracks in the rock.

Glacial drift

the general term for all of the materials carried and deposited by a glacier

Glacial outwash

Deposited in water flowing away from a melting glacier

Glacial till

unsorted deposits carried at the base of a glacier

Hydrolysis

Addition of a hydrogen atom from water to another substance

Igneous rock

rock formed from cooled magma or lava

Illuviation

Deposition in a soil layer of materials transported from a higher soil layer by percolating water

Lacustrine

Mineral sediments deposited in fresh water.

Leaching

the removal of soluble minerals by percolation

Levee

Alluvial deposit of a shallow ridge along a river, resulting from coarse deposits during flooding

Loess

wind deposited silt

Marine sediment

parent material that settled to the bottom of old oceans and seas

Metamorphic rock

rock that has been changed by heat or pressure

Mineral soil

A soil whose traits are determined mainly by its mineral content; mineral soils contain less than 20 percent organic matter.

Organic soil

Soil containing more than 20 percent organic matter. Soil properties are dominated by the organic matter.

Oxidation-reduction

Chemical reaction in which an element loses electrons to another participant in the reaction

Parent material

The unconsolidated organic and mineral material in which soil forms.

Pedology

Study of formation and classification of soil

Pedon

smallest volume that can be called a soil

Plow layer

upper part of a soil profile disturbed by humankind by plowing or other disturbances; P horizon suffix

Polypedon

group of similar pedons

Residual soil

Soil formed in place form bedrock

River terrace

a former river floodplain now at a higher elevation

Root wedging

rocks forced apart by root pressure

Sedimentary rock

Rock made of sediments hardened over time by chemicals or pressure

Slope aspect

Direction slope is facing

Soil genesis

evolution of a soil from its parent material

Solum

Upper, weathered part of the soil profile

Subsoil

soil below the plow layer, generally the B horizon

Talus

Deposits of dry rock and soil that have slid to the base of a slope under the force of gravity

Arable land

land suitable for growing crops

Diagnostic horizon

Any of a series of specific types of soil horizons used to assign a soil to its proper soil order

Great group

A taxonomic level of the current soil-classification system

Subgroup

A category below the great group category and above the family category

Suborder

A category below the order category

Biopore

Large soil macropore created by life, for example, earthworm tunnels or channels remaining after root decay.

Bulk density

Mass of oven-dry soil per unit volume, usually expressed as grams per cubic centimeter.

Duripan

A soil layer hardened and cemented by silica

Fine earth fraction

The portion of the mineral particles of soil smaller than 2 millimeters. Larger particles are considered coarse fragments. The term texture applies to the fine earth fraction.

Fragipan

Naturally occurring hard, brittle subsoil layer high in clay that restricts root growth.

Friable

easily crumbled

Gley

Soil layer that develops under poor soil drainage conditions; has gray color and mottles. Color results from chemical reduction of iron under anaerobic conditions.

Infiltration

the downward entry of water into the soil

Mottling

Spots of different colors in a soil usually indicating poor drainage

Pan

A dense, hard, or compacted layer in the soil that slows water percolation

Plinthite

A mixture of various chemicals in the soil that when exposed to cycles of wetting and drying permanently hardens to a bricklike state. Common to tropical soils.

Puddling

Dispersal of soil aggregates caused by working soil when wet, creating a massive surface layer.

Redoxymorphic feature

Soil color patterns indicating alternating reducing and nonreducing conditions (saturated/nonsaturated), such as mottles.

Soil porosity

Percentage of soil volume not occupied by solid material.

Soil separate

Classes of mineral particles less than 2.0 millimeters in diameter; includes clay, silt, and several sizes of sand.

Subsoiling

breaking up compact subsoils or pans by the use of a chisel or other tool

Tillage pan

A soil pan induced by tillage operations.

Tilth

Physical condition of the soil in terms of how easily it can be tilled, how good a seedbed can be made, and how easily seedling shoots and roots can penetrate.

Actinomycete

Order of microbes common to soil; bacteria but resemble fungi

Antagonism

The suppression of the growth of one organism by another organism by the production of toxins or grown inhibiting substances

Arthropod

Animals with no backbone, jointed body and legs, usually a hard shell

Autotroph

An organism that makes its own food

Bioremediation

Use of biological processes and agents such as plants or microbes to help degrade and clean up the environment

Detritus

Dissolved or particulate dead, but not decomposed organic material

Heterotroph

An organism that cannot make its own food.

Humus

Decay-resistant residue of organic matter decomposition, dark in color

Hyphae

Individual strands of the vegetative body of fungi, can grow in organic matter to cause decay

Immobilization

absorption of an available nutrient by a soil organism or plant, changing it to an unavailable organic form

Inoculation

Adding microbes to soil, seed, or a culture medium

Macrofauna

Larger, easily visible soil animals.

Mesofauna

Small soil animals slightly larger than microscopic, about 0.2-2 mm in size, including large nematodes and small but visible arthropods.