Introduction to Soil Descriptions Part 3 of 3

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Acknowledgement This work was supported [in part] by the National Decentralized Water Resources Capacity Development Project with funding provided by the U.S. Environmental Protection Agency through a Cooperative Agreement (EPA No. CR827881-01-0) with Washington University in St. Louis. The results have not been reviewed by EPA or Washington University in St. Louis. The views expressed in this presentation are solely those of NCSU, and University of Arkansas and EPA and Washington University in St. Louis do not endorse any products or commercial services mentioned in the presentation.

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Soil Profile Description and Horizons Rules .1939, .1941 (a4), .1943, .1944

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Soil Profile Descriptions ¾ Soil

Horizon - A layer of soil,

approximately parallel to the surface, having distinct characteristics produced by soil forming processes. ¾ Soil

Profile - A vertical section of the soil

extending through all its horizons and into the parent material.

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Soil Profile Descriptions ¾

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Soil Profile - A vertical section of the soil extending through all its horizons and into the parent material. Soil Horizon - A layer of soil, approximately parallel to the surface, having distinct characteristics produced by soil forming processes. Soil Layer - A layer in the soil deposited by a geologic force (wind, water, glaciers, oceans, etc.) and not relating to soil forming process.

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Soil Horizon Nomenclature ¾ ¾ ¾

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Soil horizons designated by a combination of: CAPITAL LETTERS-lower case letters-ARABIC NUMERALS Master Horizons and Layer: Major breaks in the soil: O, A, E, B, C, and R. Subordinate Distinctions: Lower case letters used as suffixes to designate specific master horizons. i.e. Ap, Bw, Cg Vertical Subdivisions: A horizon designated by a single combination of letters which needs to be subdivided. i.e. Bw1, Bw2, Cg1, Cg2.

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Organic (O) Horizons ¾ ¾

O horizons or layers: Layers dominated by organic material. Field Criteria z z z z

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>20% organic matter Dark color (never used by itself) Low strength, light dry weight, high fiber content Typically a surface horizon-if buried may indicate disturbance

Subordinate Distinctions of O Horizon z z z

Oa-Highly decomposed organic material (Muck) Oe-Moderately decomposed organic material (Mucky Peat) Oi-Slightly decomposed organic material (Peat)

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Pungo series, organic from top to bottom.

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A Horizons ¾

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Referred to as topsoil and typically ranging from 6-30 centimeters thick. Mineral horizon formed at the surface or below an O horizon. Characterized by an accumulation of humified organic matter intimately mixed with the mineral fraction. Field Criteria z z z z

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Mineral soil material Mix of well decomposed organic matter and mineral material Surface mineral horizon Typically dark in color-darker than underlying horizons

Typical Subordinate Distinctions of A Horizon z

Ap-Plowing or other disturbance

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A Horizon

Cecil series with poorly defined A horizon typical of the piedmont in that it is only slightly darker than the horizons below.

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Ap Horizon

Ap horizon or plow layer. Note how abrupt the transition is from the Ap to the lower horizon.

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E Horizons ¾

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Mineral horizon in the upper part of the soil typically underlying an O or A horizon. Light colored, leached horizons ranging from not being present to several centimeters thick Field Criteria z z z

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Zone of eluviation - removal of clays, Fe, Al, and humus Lighter in color than over or underlying horizon Near surface, below O or A horizons and above a B horizon

Formed by weak organic acids that strip coatings from sand grains. Light color due to the natural color of the mineral grains.

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E Horizon

Thick E horizon in a Conetoe Series. The fine reddish brown streaks are lamella composed of Fe and clay. The B horizon shows a slight increase in clay.

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E Horizon

E horizon in a Aquod (wet Spodosol). Fe and OM have been removed and translocated lower in the profile.

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A vs. E horizon ¾A

horizons have a high OM content ¾ E horizons have low OM content ¾ E horizons often feel sandier (coarser) than the A horizon ¾ E horizons have a higher value

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E vs. B horizon ¾E

horizons are sandier (coarser) than B horizons ¾ E horizons are higher in value ¾ B horizons have more clay ¾ B horizons have more Fe

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B Horizons ¾ Referred

to as subsoil. the zone of accumulation with in the soil. In well drained soils it has the brightest colors. May extend over a meter below the surface.

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B Horizons - Field Criteria ¾ ¾ ¾ ¾

Subsurface horizon formed below an O, A, E horizon and above the C horizon Formed as a result of soil forming processes Weakest expression is color development Illuvial concentration-zone of accumulation

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B Horizons - Subordinate Distinctions ¾ ¾ ¾ ¾

Bg-Strong gleying, indicates prolonged periods of saturation Bs-Illuvial accumulation of sesquioxides (spodic) Bh-Illuvial accumulation of humus (spodic) Bt-Accumulation of clay

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Bt Horizon

Bt under a lighter E horizon.

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Btg Horizon

Btg horizon at 40 cm and continuing to 100 cm. It is a g as it formed under saturated conditions and ha a matrix chroma of 2 or less. It is a t because it has a higher clay content than the Eg horizon above.

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Bh Horizon Bs Horizon

Bhs over a Bs horizon in an Aquod. Often a Bhs will overlie a Bs

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C Horizon ¾

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Referred to as substratum. These horizons and layers are little affected by soil forming processes (unweathered geologic material). Field Criteria z z z

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Little affected by soil-forming processes Geologic layering Lack of color development, color of unweathered geologic material

Subordinate Distinctions of C Horizons z

Cg-Strong gleying, indicates prolonged periods of saturation

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C horizon that looks more like rock but it offers no resistance to excavations. Note the foliation pattern is still obvious.

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Total below trench adjusted for wetness

Usable depth

Total below trench

Total depth

Ap Trench bottom depth Bw1

Soil Profile ¾

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z z

Bw3

z

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determine if restrictive by rule

Depth z

Soil wetness Bw2

2BCd Parent material Restrictive Most limiting2Cd

Horizons

to parent material to soil wetness to most limiting layer for trench bottom

Usable depths z z z

Usable depth Below trench bottom Adjustment for slope and/or wetness condition

Bt under a lighter E horizon.

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