Soil Horizons and Their Characteristics

O Horizon

Organic horizon.

A Horizon

Mineral horizon that is dark in color due to accumulation of organic matter.

E Horizon

Light in color and low in clay due to leaching.

B Horizon

Subsoil horizon altered by pedogenic processes.

C Horizon

Unaltered parent material that is soft enough to dig through.

R Horizon

Hard, unweathered bedrock.

Transitional Horizon

Combine two master horizons to indicate properties intermediate between them (e.g., AB, BA, AE, EA, BC, CB).

Horizon Prefix

Indicates if there is more than one parent material for the profile.

Subordinate Distinction 'b'

Indicates buried horizons from a soil previously exposed at the surface. Use with buried A and horizons below a buried A.

Subordinate Distinction 'g'

Indicates gray color resulting from reduction of iron oxide coatings on minerals. Use when matrix color has a value ≥4 and chroma ≤2 and redox concentrations are observed.

Subordinate Distinction 'k'

Indicates visible accumulation of secondary carbonates. Occur as bright white masses that effervesce with HCl.

Subordinate Distinction 't'

Indicates accumulation of illuvial clays. Indicated by a higher clay content than the horizon(s) above and the presence of clay films.

Subordinate Distinction 'w'

Indicates weak development of structure or color without any specific illuvial accumulation. Used only with B horizons.

Horizon Number

Used when there are two or more horizons in a row with the same master and subordinate distinction, numbered starting from the top. Otherwise, dashed.

Abrupt Boundary

Boundary distinctness is less than 2 cm.

Clear Boundary

Boundary distinctness is 2.1 to 5 cm.

Gradual Boundary

Boundary distinctness is 5.1 to 15 cm.

Diffuse Boundary

Boundary distinctness is greater than 15 cm.

Rock Fragment Modifier

Used with the soil texture class based on the percent rock by volume. Examples: 'gravelly', 'stony', 'extremely stony'.

Gravel (GR)

Rounded rock fragment with a size (diameter) of 0.2 cm - 7.5 cm.

Cobble (CB)

Rounded rock fragment with a size (diameter) of 7.6 cm - 25.0 cm.

Stony (ST) (Rounded)

Rounded rock fragment with a size (diameter) of 25.1 cm - 60.0 cm.

Bouldery (BD) (Rounded)

Rounded rock fragment with a size (diameter) of > 60.0 cm.

Channery (CH)

Flat rock fragment with a size of 0.2 cm - 15 cm.

Flaggy (FL)

Flat rock fragment with a size of 15.1 cm - 38.0 cm.

Soil Texture

Particle-size distribution. Determines how readily air and water will pass through, be held, or be blocked by the soil. Common textures include sand, silt, clay, loam, sandy loam, silt loam, clay loam.

Sand

A soil particle between 0.05 and 2.0 mm in diameter. Makes large pore spaces and allows soil to drain rapidly.

Silt

A soil particle between 0.002 and 0.05 mm diameter.

Clay

A soil particle that is less than 0.002 mm in diameter. Has more surface area for reaction and holds a lot of nutrients and water.

Soil Structure Grade: Structureless

No observable aggregation (single grain) or no orderly arrangement of natural lines of weakness (massive).

Soil Structure Grade: Weak

Breaks into very few poorly formed, indistinct peds; most peds destroyed in the process of removal.

Soil Structure Grade: Moderate

Well-formed, distinct peds when removed by hand; moderately durable.

Soil Structure Grade: Strong

Durable peds that are very evident in undisturbed soil of the pit face.

Redox Concentration

Enter "Y" if iron or manganese concentrations observed. Often appear orange or black.

Redox Depletion

Enter "Y" if redox depletions observed or if there is a reduced matrix (chroma 2 or less and value 4 or more). Often appear gray.

Moist Consistence

Evaluated in the moist state. Describes how well soil resists deformation (e.g., Loose, Very Friable, Friable, Firm).

Effervescence

Enter "Y" if matrix bubbles when dilute HCl applied. Indicates the presence of carbonates.

Hydraulic Conductivity

The ease to which gases, liquids or plant roots penetrate or pass through a layer of soil. Assessed for the surface layer and the most limiting layer.

Effective Soil Depth

Determine the upper boundary of the Cr or R horizon. If no Cr or R horizon, select "Very Deep" (> 150 cm).

Soil Wetness Class

Determine the upper boundary of the shallowest horizon with a "Y" for Redox Depl. Select the class corresponding to this depth.

Hydric Soil

A wetland soil. This pit shows clear evidence of a high water table near the soil surface. Iron depletion is a redoximorphic feature of a hydric soil.

Landform

Select one of the following choices: Upland, Floodplain, Terrace, Sandhill, Tableland.

Parent Material

The unconsolidated material from which soil develops. Select the appropriate parent material based on landform and profile characteristics (e.g., Alluvium, Till, Loess, Eolian sand, Residuum).

Slope

Measured between the stakes using the percent scale.

Hillslope Profile Position

Select one of the following: Summit, Shoulder, Backslope, Footslope, Toeslope.

Surface Runoff

Assessed based on surface hydraulic conductivity and percent slope.

Epipedon

Surface diagnostic horizon. Typically corresponds to the A horizon(s). In Nebraska, most are mollic or ochric.

Mollic Epipedon

A type of epipedon typically characterized by its dark color.

Ochric Epipedon

A type of epipedon typically lighter in color than a mollic epipedon.

Diagnostic Subsurface Horizon

A soil horizon below the epipedon with specific characteristics used in soil classification (e.g., Albic, Argillic, Cambic, Natric, Fragipan).

Albic Horizon

A subsurface horizon that is light in color and low in clay due to leaching.

Argillic Horizon

A diagnostic subsurface horizon indicating accumulation of illuvial clays. Identified by higher clay content and clay films.

Cambic Horizon

A diagnostic subsurface horizon that is altered by pedogenic processes. May show development of structure or color without specific illuvial accumulation.

Fragipan

A dense, brittle layer often found in the B horizon. Characterized by bleached vertical streaks and can restrict root and water movement. Indicated by 'Bx' notation in a pit description.

Lithic Contact

Corresponds to the R horizon.

Paralithic Contact

Corresponds to the Cr horizon.

Slickensides

Polished/grooved surfaces produced when soil aggregates slide past one another due to shrinking and swelling of soil rich in smectite clays.

Aquic Conditions

Presence of redox features within the upper 50 cm.

Soil Map Unit

A delineation on a soil map representing an area dominated by one or more major kinds of soil or miscellaneous areas.

Web Soil Survey (WSS)

Provides interactive access to the most current official information about the soils in a given area. Can generate soil maps and reports.

Area of Interest (AOI)

A user-defined area in Web Soil Survey for which soil data is accessed.

Nutrient Management

Management of the amount, source, placement, and form of plant nutrients and soil amendments applied to soils to obtain optimum yields and minimize the risk of surface- and ground-water pollution.

Comprehensive Nutrient Management Plan (CNMP)

A conservation plan unique to an animal-feeding operation (AFO) that incorporates practices to help ensure production and natural resource protection goals are met.

Contour Stripcropping

Alternating strips of cultivated crops and perennial vegetation that are farmed on the contour. Can reduce soil erosion by as much as 50 percent.

Buffer Strips

Areas or strips of land where a permanent cover of vegetation is maintained to help control pollutants and manage other environmental problems.

Grassed Waterway

A natural or constructed vegetated channel that is shaped and graded to carry surface water at a nonerosive velocity to a stable outlet.

Windbreak or Shelterbelts

Consist of a single row or multiple rows of trees or shrubs that protect the soil from wind erosion.

Terraces

Structures that break long slopes into shorter ones and generally follow the contour, serving as small dams to intercept and guide water.

Cover Crop

Growing a crop of grass, small grain, or legumes primarily for seasonal protection and soil improvement.

Similarity Index

Expresses the percentage of a desired plant community present on the site. Calculated by comparing the actual weight of species present to the expected production in the desired community.

Active Fraction

Component of the soil having an ion exchange capacity, specifically clay and organic matter.

Alluvium

Unconsolidated, clastic material subaerially deposited by running water (channel flow).

Colluvium

Unconsolidated, unsorted earth material being transported or deposited on side slopes and/or at the base of slopes by mass movement.

Eolian Deposit

Material transported and deposited by the wind. Includes dune sands, sand sheets, loess deposits, and clay.

Loess

Material transported and deposited by wind and consisting predominantly of silt-size particles.

Residuum

(residual soil material) Unconsolidated, weathered, or partly weathered mineral material that accumulates by disintegration of bedrock in place.

Till (Glacial)

Dominantly unsorted and unstratified drift, generally unconsolidated and deposited directly by a glacier. Consists of a mixture of clay, silt, sand, gravel, stones, and boulders.

Soil Management

The sum total of how we prepare and nurture soil, select suitable crops, tend the crop and soil together, and add fertilizer/materials to maintain productivity and preserve soil.

Soil Profile

The sequence of natural layers, or horizons, in a soil. It extends from the surface downward to unconsolidated material.

Soil Forming Factors

The surrounding environment that leads to differences in soil properties. The factors include Parent Material, Climate, Relief (Topography), Biological Activity, Time, and in some cases, Human Activity.

Soil Scientist

A scientist who studies the upper few meters of the Earth's crust, including its physical and chemical properties, distribution, genesis, morphology, and biological components.