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A horizon

Generally the first to form in immature soil.

Colluvium

An example of parent material moved by gravity.

Erosion

An example of one of the four soil forming processes.

Subordinate designation

Indicates a soil horizon with evidence of disturbance by agricultural activities.

B horizon

The zone where maximum eluviation occurs.

Crysol

Not one of the recognized soil orders.

Loessification

Not considered one of the four general processes of soil genesis.

Organic matter accumulation

Most pronounced in the A horizon.

Chemical weathering

Greatest in hot and moist climates.

Water

Essential for the dissolution of primary minerals necessary for soil development.

E horizon

Characterized by strong eluvial properties.

Moisture regimes

Ranked from driest to wettest as aridic, udic, aquic.

Additions

Deposition of colluvial parent material as a soil forming process.

Climate

Influences the rate of weathering and type of native vegetation.

Gelisols

Soils that are permanently frozen.

Oxisols

Highly weathered soils more so than any other order.

Entisols

Soils with little or no morphological development.

Residual parent materials

Most likely found at the summit of a steep hill.

Tropical forests

Protect soil from excessive weathering.

Folistic epipedon

Layer of organic soil not saturated with water for more than 30 days.

Physical weathering

Increases surface area of soil minerals.

Colluvium

A parent material that lacks properties associated with sorting actions of water or wind.

Oxisol

Soils dominated by minerals resistant to weathering.

Histic epipedon

Layer of organic soil that is naturally saturated with water.

Soil moisture regime

Aquic has the highest moisture levels.

Soil Taxonomy

Specifies 12 soil orders, 4 of which are primarily comprised of organic soils.

Natural Resources Conservation Service

The lead agency for most soil survey work in the United States.

Epipedon

A horizon that forms at or near the surface, often darkened by organic matter.

Anthropic epipedon

Similar to mollic in color and structure but formed through human activity.

Histic epipedon

Contains organic soil material that is saturated with water.

Melanic epipedon

A dark mineral horizon characteristic of soils from volcanic ash.

Mollic epipedon

Humus-rich surface horizon with dominant bivalent cations.

Ochric epipedon

Fails to meet criteria for other epipedons and is too light, thin, or low in organic matter.

Umbric epipedon

Dark, humus-rich surface horizon with less than 50% base saturation due to leaching.

Soil Horizons

Include O (Organic), A (Surface), B (Subsoil), C (Substratum), E (Master horizon), R (Bedrock).

Colluvium, Alluvium, Loess

Types of parent materials moved by gravity, water, and wind respectively.