Soils Glossary Appendix


APPENDIX 1 - TABULAR INFORMATION

Table A1. Outline of the U.S. soil classification system (Soil taxonomy) revised 8/17/94:

Table A2. Prefixes and their connotations for names of great groups in the U.S. soil classification system (Soil taxonomy) - PDF

Table A3. Classification scheme for phyllosilicates related to clay minerals - PDF

APPENDIX II-DESIGNATIONS FOR SOIL HORIZONS AND LAYERS

Three kinds of symbols are used in combination to designate horizons and layers. These are capital letters, lower case letters, and arabic numbers; capital letters are used to designate master horizons and layers; lower case letters are used as suffixes to indicate specific characteristics of the master horizon and layer; arabic numerals are used both as suffixes to indicate vertical subdivisions within a horizon or layer and as prefixes to indicate discontinuities (Soil survey manual, Issued October 1993. This is a revision and enlargement of USDA Handbook No. 18, the Soil Survey Manual issued October 1962, and supersedes it. Reference is also made to Keys to soil taxonomy, 6th ed. issued, 1994). Genetic horizons are not the equivalent of the diagnostic horizons of the U.S. soil taxonomy. Designations of genetic horizons express a qualitative judgment about the vector of changes that are believed to have taken place. Diagnostic horizons are quantitatively defined features used to differentiate between taxa in U.S. system of soil taxonomy. Horizon symbols indicate the direction of presumed pedogenesis while diagnostic horizons indicate the magnitude of that expression.

Master Horizons and Layers

O horizons-Layers dominated by organic material.

A horizons-Mineral horizons that formed at the surface or below an O horizon that exhibit obliteration of all or much of the original rock structure and (i) are characterized by an accumulation of humified organic matter intimately mixed with the mineral fraction and not dominated by properties characteristic of E or B horizons; or (ii) have properties resulting from cultivation, pasturing, or similar kinds of disturbance.

E horizons-Mineral horizons in which the main feature is loss of silicate clay, iron, aluminum, or some combination of these, leaving a concentration of sand and silt particles of quartz or other resistant materials.

B horizons-Horizons that formed below an A, E, or O horizon and are dominated by obliteration of all or much of the original rock structure and show one or more of the following:

  1. illuvial concentration of silicate clay, iron, aluminum, humus, carbonates, gypsum, or silica, alone or in combination;
  2. evidence of removal of carbonates;
  3. residual concentration of sesquioxides;
  4. coatings of sesquioxides that make the horizon conspicuously lower in value, higher in chroma, or redder in hue than overlying and underlying horizons without apparent illuviation of iron;
  5. alteration that forms silicate clay or liberates oxides or both and that forms granular, blocky, or prismatic structure if volume changes accompany changes in moisture content; or
  6. brittleness.

C horizons or layers-Horizons or layers, excluding hard bedrock, that are little affected by pedogenic processes and lack properties of O, A, E, or B horizons. The material of C horizons may be either like or unlike that from which the solum presumably formed. The C horizon may have been modified even if there is no evidence of pedogenesis.

R layers-Hard bedrock including granite, basalt, quartzite and indurated limestone or sandstone that is sufficiently coherent to make hand digging impractical.

Transitional Horizons

Two kinds of transitional horizons are recognized. In one, the horizon is dominated by properties of one master horizon but has subordinate properties of another. Two capital latter symbols are used, such as AB, EB, BE, or BC. The master horizon symbol that is given first designates the kind of master horizon whose properties dominate the transitional horizon. In the other, distinct parts of the horizon have recognizable properties of the two kinds of master horizons indicated by the capital letters. The two capital letters are separated by a virgule (/), as E/B, B/E, or B/C. The first symbol is that of the horizon that makes up the greater volume.

  • AB - A horizon with characteristics of both an overlying A horizon and an underlying B horizon, but which is more like the A than the B.
  • EB - A horizon with characteristics of both an overlying E horizon and an underlying B horizon, but which is more like the E than the B.
  • BE - A horizon with characteristics of both an overlying E horizon and an underlying B horizon, but which is more like the B than the E.
  • BC - A horizon with characteristics of both an overlying B horizon and an underlying C horizon, but which is more like the B than the C.
  • CB - A horizon with characteristics of both an overlying B horizon and an underlying C horizon, but which is more like the C than the B.
  • E/B - A horizon comprised of individual parts of E and B horizon components in which the E component is dominant and surrounds the B materials.
  • B/E - A horizon comprised of individual parts of E and B horizon in which the E component surrounds the B component but the latter is dominant.
  • B/C - A horizon comprised of individual parts of B and C horizon in which the B horizon component is dominant and surrounds the C component.

 

 Subordinate Distinctions Within Master Horizons and Layers

  • a - Highly decomposed organic material where rubbed fiber content averages <1/6 of the volume.
  • b - Identifiable buried genetic horizons in a mineral soil.
  • c - Concretions or nodules with iron, aluminum, manganese or titanium cement.
  • d - Physical root restriction, either natural or manmade such as dense basal till, plow pans, and mechanically compacted zones.
  • e - Organic material of intermediate decomposition in which rubbed fiber content is 1/6 to 2/5 of the volume.
  • f - Frozen soil in which the horizon or layer contains permanent ice.
  • g - Strong gleying in which iron has been reduced and removed during soil formation or in which iron has been preserved in a reduced state because of saturation with stagnant water.
  • h - Illuvial accumulation of organic matter in the form of amorphous, dispersible organic matter-sesquioxide complexes.
  • i - Slightly decomposed organic material in which rubbed fiber content is more than about 2/5 of the volume.
  • k - Accumulation of pedogenic carbonates, commonly calcium carbonate.
  • m - Continuous or nearly continuous cementation or induration of the soil matrix by carbonates (km), silica (qm), iron (sm), gypsum (ym), carbonates and silica (kqm), or salts more soluble than gypsum (zm).
  • n - Accumulation of sodium on the exchange complex sufficient to yield a morphological appearance of a natric horizon.
  • o - Residual accumulation of sesquioxides.
  • p - Plowing or other disturbance of the surface layer by cultivation, pasturing or similar uses.
  • q - Accumulation of secondary silica.
  • r - Weathered or soft bedrock including saprolite; partly consolidated soft sandstone, siltstone or shale; or dense till that roots penetrate only along joint planes and are sufficiently incoherent to permit hand digging with a spade.
  • s - Illuvial accumulation of sesquioxides and organic matter in the form of illuvial, amorphous, dispersible organic matter-sesquioxide complexes if both organic matter and sesquioxide components are significant and the value and chroma of the horizon are >3.
  • ss - Presence of slickensides.
  • t - Accumulation of silicate clay that either has formed in the horizon and is subsequently translocated or has been moved into it by illuviation.
  • v - Plinthite which is composed of iron-rich, humus-poor, reddish material that is firm or very firm when moist and that hardens irreversibly when exposed to the atmosphere under repeated wetting and drying.
  • w - Development of color or structure in a horizon but with little or no apparent illuvial accumulation of materials.
  • x - Fragic or fragipan characteristics that result in genetically developed firmness, brittleness, or high bulk density.
  • y - Accumulation of gypsum.
  • z - Accumulation of salts more soluble than gypsum.