Soil Horizons, Properties, and Pedogenic Processes - Vocabulary Flashcards

A set of vocabulary flashcards covering soil horizons, soil properties (color, texture, structure), drainage indicators, soil components, and key pedogenic processes.

Pedon

A 3-dimensional body of soil.

Profile

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

Horizon

The name for a horizontal layer of soil which differs in features from layers around it.

O horizon

The organic horizon at the surface of many soils, composed of organic detritus in various stages of decomposition.

A horizon

Mineral horizon at the surface or below O.

E horizon

The Eluvial horizon, the loss of organic matter, clay, iron, and/or aluminum.

B horizon

The Illuvial horizon, subsurface horizon of clay and iron accumulation.

C horizon

The parent material, unweathered and unconsolidated.

R horizon

Consolidated bedrock.

Consolidated material

Solid and coherent (rocks).

Unconsolidated material

Material not bound into one solid mass.

Solum

Horizons that form from the parent material (A, E, and B).

Eluviation

Washing out of fine soil components (clay, iron, aluminum).

Illuviation

Deposition of fine soil components (clay, iron, aluminum).

Soil horizons

O, A, E, B, C, R — the set of distinct soil layers in a profile.

Color

The classification of Hue, Value, and chroma of soil.

Hue

The ratio of yellow to red in a soil.

Value

How light or dark the color of a soil is.

Chroma

The brightness or purity of color in a soil.

Munsell notation

Color notation using Hue, Value, and Chroma (e.g., 2.5YR 4/6).

Texture

The percentage of sand, silt, and clay that make up a soil.

Structure

The arrangement of soil particles into aggregates.

Oxidized iron (Fe3+)

Iron in the ferric state; indicates red colors and usually good drainage.

Reduced iron (Fe2+)

Iron in the ferrous state; indicates gray colors and often poor drainage.

Mottling

Mixture of different colors in a soil, indicating imperfect drainage (redoximorphic features).

Matrix

The background color of a soil horizon.

Soil

The unconsolidated mineral and organic material on the immediate surface of the earth; where lithosphere, hydrosphere, and biosphere meet.

Rock

A mineral that is greater than 2 mm in diameter.

Sand

Particles 2 to 0.05 mm in size.

Silt

Particles 0.05 to 0.002 mm in size.

Clay

Particles smaller than 0.002 mm.

Differentiation

Accumulated change in soil leading to distinct horizons.

Additions

Deposition and littering of material onto the soil.

Losses

Leaching and erosion removing material from the soil.

Translocations

Movement of soil components within the profile (eluviation, illuviation, pedoturbation, salinization, alkalization).

Transformations

Changes such as weathering, decomposition, humification, mineralization, and synthesis.

Deposition

Wind or water additions of soil material.

Littering

Accumulation of organic material on the soil.

Leaching

Removal of soluble material from the soil.

Erosion

Removal of the surface layer of soil.

Pedoturbation

Biological or physical mixing of soil materials.

Salinization

Accumulation of soluble salts in the soil.

Alkalization

Accumulation of sodium in the soil.

Weathering

Changes to rocks and minerals due to exposure to climate elements.

Decomposition

Breakdown of mineral and organic materials.

Humification

Conversion of organic matter into humus.

Mineralization

Release of mineral constituents from organic materials.

Synthesis

Formation of a new mineral or organic species.

what soil texture is more dense, clay or sand.

clay due to aggregates forming more micropores

granular soil structure

small roughly rounded aggregates

blocky soil structure

small blocky aggregates

Prism like Soil structure

aggregates are taller than they are wide. divided into round columnar or sharp edged prismatic structures.

Platy soil structure

Soil aggregates that are wider than they are tall

Structureless soil structure

Either single grained with no aggregation or Massive aggregates with no distinct weak points in structure

types of soil structure

Granular, Blocky, Prism like, Platy, and Structureless

Parent material structure is usually…

Structureless

Granular soil is most common in…

The A Horizon

Blocky Soil Structure is most common in..

the B Horizon

Prism Like Soil Structure is most common in..

Dry Arid environments

Platy Soil Structure is most common in..

E Horizons under highly compacted conditions

Parent Material

The Material that soil is originating from (Neither Rock nor Soil)

Density is measured in

g/cm³

Particle Density

Density of solid particles only, excludes pore space, water, and organic matter

Bulk Density

Density of dry soil including pore space and organic mater

Calculating porosity

1-(bulk density/particle density)

Volume calculation from a corer

Pi*r²*h (answer must be in cm³)

Which Soil Horizon is the most dense

B Horizon

Macropore diameter

>0.06mm

Micropore diameter

<0.06

What soil type is best for agriculture

Loam due to equal parts Macro and Micropores

What soil type is best for Construction

High density soils

Soil Water Potential

The work of water as it moves from present state to free pool

The kPa of water at free pool

greater then 0

The kPa of water at saturation

0

The kPa of absorbed water

less than 0

the maximum kPa value for absorbed water

-800,000

Soil Gravimetric Water Content

mass of water/ mass of dry soil

Soil Volumetric Water Content

mass of water/ 1g/cm³

What will be higher, Soil Gravimetric Water Content or Soil Volumetric Water Content?

Soil Volumetric Water Content

Free Pool

Soil that is completely saturated

Field Capacity

The greatest amount of water that can be held against gravity

Field Capacity kPa range

-10 to -33

Permanent Wilting point

the point of resistance in which roots can no longer extract water from soil

Permanent Wilting Point kPa value

-1500

Tensiometer

tool used to measure SWP

Matric Water Potential

the force of Adhesion and Cohesion on water

Adhesion

Water’s attraction to itself

Cohesion

Water’s attraction to surfaces

Osmotic Water Potential

The attraction of water to solvents

Pressure Water Potential

Gas pressure effects on water

Gravitational Water Potential

Downward movement of water in response to gravity

Soil Consistency

Degree to which soil deforms

Shear Strength

The Atterberg limits of a soil

Atterberg limits

Shrinkage limit, plastic limit, and liquid limit

Shrinkage Limit

The exact water content at which soil no longer shrinks as it dries

Plastic Limit

The exact water content at which soil transitions from a crumbly solid state to a malleable plastic state

Liquid Limit

The exact water content at which soil begins to behave as a liquid instead of a moldable plastic