Soil Formation Exam 1

Abrupt Textural Change

A considerable increase in clay content over a short vertical distance

Agric Horizon

Subsoil horizon with an accumulation of silt, clay, and humus

Albic Materials

Soil materials whose color is determined by uncoated primary sand and silt particles

Andic Soil Properties

Unique soil properties associated with materials that are rich in volcanic glass or poorly crystalline minerals

Anhydritic Horizon

Horizon with an accumulation of anhydrite

Anhydrous Conditions

Very cold and very dry soil conditions

Aquic Conditions

Saturation in the soil to the extent that it results in the depletion of oxygen

Aquic Moisture Regime

Regime characteristic of poorly and very poorly drained soils

Argillic Horizon

Subsoil horizon with an illuvial accumulation of clay

Aridic (Torric) Moisture Regime

Regime characteristic of arid and semiarid climates that are unsuitable for cultivation without irrigation

Calcic Horizon

Subsoil horizon with an illuvial accumulation of calcium carbonate

Cambic Horizon

Subsoil horizon with minimal development

Coefficient of Linear Extensibility (COLE)

A measure describing the proportional change in linear dimension of a soil clod due to shrinking and swelling

Cryoturbation

Intense frost churning

Densic Contact

The contact between unconsolidated soil material and the underlying root-restrictive, dense, compact materials

Densic Materials

Root-restrictive, noncemented, dense, compact material

Duripan

Subsoil layer that is cemented by silica

Fragipan

A root-restrictive subsoil layer that is firm and brittle, but not cemented

Fibric Soil Materials

Organic soil materials that are only slightly decomposed

Gelic Materials

Soil materials (mineral or organic) above permafrost that show evidence of frost churning

Glacic Layer

Layer of ice in the soil

Glossic Horizon

A degrading argillic, kandic, or natric horizon in which loss of clay and iron oxide is occurring

Pedology

a natural science that concerns itself to a great extent with the biogeochemical processes that form and distribute soils across the globe

Soil Profiles

two dimensional vertical exposures of the layering of soils
features result from unique combination of the factors of soil formation: climate, biota, topography, parent material, and time

Soil Horizons

soil layers

Silicate

Most soils are dominated by ____ minerals.

by comparing a soil sample(either in a crushed state or intact soil fragment or ped) with a color chip in a Munsell color chart in both a wet and dry state

How is soil color determined?

darkens soil, decreases Munsell color value

What does soil organic matter content do to a soil’s color?

dependent on amount, but will redden as they age due to increased amounts of chemical weathering and increased concentration of iron oxide

What does iron oxide content do to a soil’s color?

turns more white, increases value of Munsell color

What does calcium carbonate content do to a soil’s color?

Soil Texture

estimate of relative proportions of sand, silt, and clay in a sample

usually determined by texture feel test

Aggregates

individual mineral particles combined by binding with organic matter, oxides, and/or clay

-the chemical evolution of the universe and the solar system

-chemical differentiation of the planet

-the effects of soil formation

What 3 principal processes led to the chemical composition of average soil?

O, Si, Al, Fe, Ca, Na, Mg, K

8 most abundant elements in soil crust:

elemental

Few, if any, of the important elements in Earth’s crust are found in an _____ state.

O and Si

2 most abundant elements in the crust and soils(in terms of mass)

silica tetrahedron

one Si atom surrounded by four O atoms

O, Si, and Al

It is ___, ____, and to a lesser degree ___-dominated chemistry of the Earth’s crust that dictates that the basic mineralogy group of the Earth’s crust will be the silicates.

Neosilicates

silica tetrahedrons present as independent entities (Si:O = 1:4)

Sorosilicates

two silica tetrahedrons linked together by sharing 1 oxygen (Si:O = 1:3)

Cyclosilicates

silica tetrahedrons share two oxygens with adjoining tetrehedrons, forming a closed ring structure (Si:O = 1:3)

Inosilicates

tetrahedorns are joined to form either single chains (Si:O = 1:3) or double chains (Si:O = 4:11)

Phyllosilicates

3 oxygens of each tetrahedron are shared with adjacent tetrahedrons to form sheets (Si:O = 2:5)

Tectosilicates

every tetrahedron shares its corner with other tetrahedrons, forming 3D network (Si:O = 1:2)

increases

as the temperature of the mineral formation decreases, the complexity of silica tetrahedral linkages ______.

increase

Decreasing Si/O ratios (including tetrahedral linkages) ______ weathering resistance.

increase

Decreasing Si/Al ratios ______ weathering resistance.

decreases

Presence of Fe+2 in minerals ____ stability.

chemical composition and chemical behavior

What are the primary differences between primary and secondary silicates?

number of sheets of tetrahedrally and octahedrally coordinated O that the mineral has

First major means of classifying secondary phyllosilicates

chemical composition of elements around which O atoms are coordinated

Second most important characteristic of each type of mineral

Oxides

Relatively moist and warm environments favor the development of significant quantities of _____

Carbonates

_____ are favored in environments with low desilication potential

Chemical Weathering

chemical altering of parent material through water and sometimes acid acting as a solvent of silicate mineral

-total chemical analysis

-extractive chemical and associated physical analyses

2 categories for soil chemical property measurements:

-particle size determination

-bulk density and moisture

-water content

-carbon and cations

-cation exchange capacity (CEC) and bases

-salt

-pH and carbonates

-phosphorous

-clay minerology

-sand and silt minerology

NCRS data report tiers:

particle size analysis (PSA)

quantification of size distribution of minerals and rock fragments in a soil

-sum of absorbed cations

-displacement of an absorbed cation

2 methods that determine CEC