Soil Development, Formation, Horizons, and Parent Materials Flashcards

Comprehensive 100-card vocabulary flashcard deck covering soil development, forming processes, horizon designations, physical/chemical weathering, mineral and rock properties, and the CLORPT soil-forming factors.

Soil Formation

The process of creating soil from "not soil" (parent material); synonymous with soil genesis.

Parent Material

The unconsolidated and chemically weathered mineral or organic matter from which the solum of soils develops.

Transformations

Soil-forming processes occurring when soil constituents are chemically or physically modified or destroyed and new minerals or compounds are synthesized.

Translocations

Soil-forming processes involving the transfer or movement of inorganic and organic materials laterally within a horizon or vertically between horizons.

Additions

Inputs of materials to the soil profile from outside sources, such as organic matter, flood sediments, or aeolian deposits.

Losses/Removals

The removal of soil materials from the profile through processes such as leaching, surface erosion, evaporation, or gaseous emissions.

Weathering

Any of the chemical or physical processes by which rocks undergo chemical decomposition and physical disintegration at or near the Earth's surface.

Physical Weathering

The breakdown of rock and mineral particles into smaller fragments purely by physical forces without chemical alteration.

Subsidence

Ground settling or sinking resulting from shrinkage and swelling cycles of clays under foundation structures.

Unloading

Physical weathering process where the removal of a heavy overlying load (such as a melting glacier) causes underlying soil or rock to uplift and expand.

Chemical Weathering

The process by which rocks are decomposed, dissolved, or loosened by chemical reactions to form residual materials.

Hydration

Chemical weathering process where minerals absorb water into their crystal structure and expand, creating internal stress that disintegrates rocks.

Hydrolysis

Chemical reaction between rock minerals and water where water molecules split into $H^+$ and $OH^-$ ions, and $H^+$ replaces a cation in the mineral structure.

Carbonation

Chemical weathering process where carbon dioxide dissolved in rainwater forms carbonic acid, which reacts with and weakens rock minerals.

Dissolution

Chemical weathering process where minerals dissolve directly in water, separating into ions in solution that are transported away.

Oxidation

Chemical weathering reaction occurring when oxygen combines with elements in rocks (such as iron) to form soft, highly alterable new minerals.

Reduction

The reverse of oxidation taking place under waterlogged, anaerobic conditions, converting ferric iron to ferrous compounds and shifting soil color to grey or blue.

Biological Weathering (Acid Reactions)

Process where natural organic acids (from vegetation/microbes) or anthropogenic acids dissolve and accelerate the breakdown of minerals.

Hardpan

A dense, clay-rich soil layer at or below the surface cemented by silica, iron oxide, calcium carbonate, or organic matter that does not soften in water.

Duripan

A root-restrictive subsoil hardpan layer that is primarily cemented by illuvial silica.

Chelation

Process where metal ions such as $Fe$ and $Al$ combine with organic molecules from humus to form soluble complexes that readily transport through the pedon.

Eluviation

The movement or washing out of soil material out of a portion of a soil profile.

Illuviation

The movement or accumulation of washed-out soil material into a lower portion of a soil profile.

Leaching (Depletion)

General term for the washing out or eluviating of soluble materials from the solum.

Enrichment

General term for the addition of material to a soil body.

Cumulization

Aeolian, hydrologic, and human-made additions of mineral particles to the surface layer of a soil solum.

Decalcification

Chemical reactions that remove calcium carbonate ($CaCO_3$) from one or more soil horizons.

Calcification

Processes involving the accumulation of calcium carbonate ($CaCO_3$) in Ck and other soil horizons.

Salinization

The accumulation of soluble salts (such as sulfates and chlorides of calcium, magnesium, sodium, and potassium) in salic horizons.

Desalinization

The removal of soluble salts from salic soil horizons.

Alkalization (Solonization)

The process involving the accumulation of sodium ions ($Na^+$) on exchange sites within a soil.

Dealkalization (Solodization)

The leaching of sodium ions ($Na^+$) and soluble salts from natric soil horizons.

Lessivage

The mechanical migration of small mineral particles from A to B horizons, producing relative clay enrichment in B horizons (argillic horizons).

Pedoturbation

Biological or physical (freeze-thaw and wet-dry) churning and cycling of soil materials that homogenizes the solum.

Podzolization

Chemical migration of aluminum, iron, and/or organic matter, leading to the concentration of silica ($SiO_2$) in the eluviated horizon.

Desilication

Chemical migration of silica ($SiO_2$) out of the solum, resulting in a residual concentration of sesquioxides such as goethite and gibbsite.

Resilication

Formation of kaolinite from gibbsite in the presence of excess dissolved $Si(OH)_4$, or smectite from kaolinite at higher pH values.

Melanization

The darkening of light-colored initial unconsolidated mineral materials by the admixture of organic matter.

Leucinization

The paling of soil horizons due to the disappearance or removal of dark organic materials.

Littering

The accumulation of organic litter and associated humus on the mineral soil surface to a depth of less than $30\,cm$.

Humification

The advanced biological transformation of raw organic material into stable, dark humus.

Paludization

The accumulation of deep ($>30\,cm$) deposits of organic material, producing muck and peat soils (Histosols).

Ripening

Chemical, biological, and physical changes occurring in organic soil after air penetrates previously waterlogged material.

Mineralization

The release of inorganic nutrients and oxide solids through the breakdown of organic matter.

Gleization

The reduction of iron under anaerobic, waterlogged conditions, yielding bluish to greenish-gray matrix colors in soil.

Soil Profile

A vertical section or cross-section of the soil that exposes all of its distinct horizons.

Soil Horizon

A layer of soil parallel to the land surface that differs in physical, chemical, and biological properties from adjacent layers.

Solum

The upper, pedogenically active layers of a soil profile above the C horizon (comprising A, E, and B horizons).

O Horizon

A surface layer composed almost entirely of organic matter, common in forests and wetland bogs.

Oi Horizon

A subordinate O horizon characterized by predominantly undecomposed plant litter.

Oe Horizon

A subordinate O horizon consisting of moderately decomposed organic materials.

Oa Horizon

A subordinate O horizon consisting of highly or almost completely decomposed organic matter.

A Horizon

A mineral surface horizon darkened by the incorporation and coating of colloidal decomposed organic matter.

Ap Horizon

A surface mineral horizon that has been disturbed or modified by agricultural plowing.

E Horizon

A light-colored subsurface zone of eluviation stripped of organic matter, clay, and iron.

Bt Horizon

A subsurface B horizon characterized by the illuvial accumulation of silicate clay.

Bhs Horizon

A dark red illuvial subsurface horizon showing accumulation of organic humus ($h$) and sesquioxides ($s$).

Bw Horizon

A subsurface horizon that has undergone physical/chemical alteration in color or structure without significant illuvial clay accumulation.

Bk Horizon

A subsurface B horizon containing significant illuvial accumulations of calcium carbonate ($CaCO_3$).

C Horizon

Unconsolidated, weathered parent material located outside the zone of major pedogenic development.

R Horizon

A layer of hard, unweathered, consolidated bedrock beneath the soil profile.

Cleavage

The physical property describing a mineral's tendency to split cleanly along definite structural planes.

Streak

The color of fine powder left behind when a mineral is scraped against an unglazed porcelain plate.

Mohs Hardness Scale

A qualitative ranking scale of relative mineral scratch resistance, ranging from 1 (talc) to 10 (diamond).

Calcite

A calcium carbonate mineral ($CaCO_3$) with a Mohs hardness of 3 that effervesces readily in cold dilute $HCl$.

Dolomite

A calcium magnesium carbonate mineral ($CaMg(CO_3)_2$) whose powdered form effervesces slowly in cold dilute $HCl$.

Gypsum

A hydrous calcium sulfate mineral ($CaSO_4 \cdot 2H_2O$) with a hardness of 2 and a vitreous to pearly luster.

Magnetite

A black iron oxide mineral ($Fe_3O_4$) with a Mohs hardness of 5.5 to 6.5 that is strongly attracted by a magnet.

Hematite

A ferric iron oxide mineral ($Fe_2O_3$) yielding a characteristic brownish-red streak.

Quartz

A highly resistant silica mineral ($SiO_2$) with a hardness of 7, serving as the dominant constituent of sand.

Orthoclase Feldspar

A potassium aluminum silicate mineral ($KAlSi_3O_8$) that makes up 60% of igneous rocks and supplies potassium ($K$) to soil.

Albite

A sodium plagioclase feldspar mineral ($NaAlSi_3O_8$) displaying fine parallel striations on cleavage surfaces.

Biotite

A black mica complex silicate containing potassium, iron, aluminum, and magnesium with perfect single-direction cleavage.

Kaolinite

A secondary hydrous aluminum silicate clay mineral ($Al_4Si_4O_{10}(OH)_8$) that becomes plastic when moistened and adheres to the tongue.

Aphanitic Rocks

Igneous rocks with microscopic crystals formed from rapid cooling on the surface, yielding finely-textured clayey soils.

Phaneritic Rocks

Igneous rocks with coarse, visible crystals formed from slow cooling underground (e.g., granite).

Primary Minerals

Minerals present in rocks that have not been chemically altered since crystallizing from molten lava or deposition.

Secondary Minerals

Minerals resulting from the chemical decomposition or re-precipitation of primary mineral breakdown products.

Residual (Sedentary) Parent Material

Unconsolidated material that developed in place (in situ) directly from the underlying bedrock.

Intrusive Igneous Rocks

Plutonic rocks characterized by large crystals formed from slow cooling within the Earth's crust (e.g., granite).

Extrusive Igneous Rocks

Volcanic rocks comprised of small crystals formed from lava that cooled rapidly on the Earth's surface (e.g., basalt).

Alluvium

Parent material transported and deposited by moving water in rivers or along river banks.

Lacustrine Deposits

Parent materials carried by water and deposited in lakes, with fine silts and clays setting in deep water.

Marine Deposits

Parent materials carried by water and wave action that accumulate in oceans and coastal environments.

Aeolian Deposits

Wind-transported parent materials composed primarily of sand-sized particles carried over relatively short distances.

Loess

Wind-blown parent material consisting mainly of silt-sized particles carried over long distances.

Colluvial Deposits (Colluvium)

Coarse, unsorted rock and soil fragments that move downslope under gravity and collect at mountain bases.

Glacial Till (Drift)

Unsorted and unstratified sediment mixture of boulders, gravel, sand, and clay deposited directly by glacial ice.

Cumulose (Organic) Deposits

Organic parent materials formed in place from plant residues preserved under waterlogged, saturated conditions.

Peat

Undecomposed or slightly decomposed organic parent material preserved under high water table conditions.

Muck

Highly decomposed organic parent material accumulated under saturated conditions.

Climate (Soil Factor)

The primary factor influencing physical and chemical weathering, driven mainly by precipitation and temperature.

10°C Biochemical Rule

The principle stating that for every $10^\circ\text{C}$ rise in soil temperature, the rate of biochemical reactions doubles.

Biota (Living Organisms Factor)

The soil-forming factor consisting of vegetation, microbes, and animals that fix carbon, cycle nutrients, and mix soil.

Crown Drip

Vegetation process where foliage intercepts rainfall, adding absorbed cations and anions to the water falling to the soil.

Bioturbation

The biological mixing of organic material and upper mineral soil particles by living organisms.

Topography (Relief Factor)

The soil-forming factor related to landscape position, slope steepness, aspect, and water table depth.

Slope Aspect

The compass direction a slope faces, influencing local temperature, moisture, and soil development depth.

Time (Soil Factor)

The duration of pedogenesis reckoned from when parent material is deposited and plant life begins.

Humans (6th Soil Factor)

Human activity acting as a soil-forming factor by intentionally creating or extensively modifying soils.