Diagnostic horizons

Two basic concepts are used in developing the naming of different soils. First is the idea that a soil s characteristics will determine which group it falls into and its name. Another idea is that soils will be related to a reference soil. In both cases, the natural soil horizons are used in the soil description. In Soil Taxonomy, horizons used for naming the soil are called diagnostic horizons. In the reference soils, the horizons are called reference horizons. The general concepts are similar in all systems, and so are many names for soil characteristics. The names are often descriptive in that they give an idea of the characteristic of the soil. 

Gonzalez-Perez, J. A., Arbelo, C. D., Gonzalez-Vila, F. J., Rodriguez, A. R., Almendros, G., Armas, C. M., and Polvillo, O. (2007). Molecular features of organic matter in diagnostic horizons from andosols as seen by analytical pyrolysis. J. Anal. Appl. Pyrolysis 80, 369-382. 

FIGURE 1. Illustrations of soil variability at different spatial scales. At the regional scale, variability is expressed by the difference of different soil mapping units within a soil map sheet (a). At the scale of the soil profile, variability is observed by the presence of different diagnostic horizons (b). Within the soil horizons, variability is presented by the heterogeneous appearance of soil aggregates (c). Within aggregates, microscopic variability is observable in the porous structure (d). 

Rendzinae — these are formed at different altitudes and climatic conditions on carbonate and ultrabasic rocks. The main diagnostic horizons ... 

Epipedon. The diagnostic horizons that occur at the soil surface. This represents the surface horizon of soil profile. 

Entisols. Mineral soils that have no distinct subsurface diagnostic horizons within 1 m of the soil surface. Entisols have little or no evidence of the development of pedogenic horizons. Most Entisols have no diagnostic horizons other than an ochric epipedon. Entisols are divided into five suborders Aquents, Arents, Psamments, Fluvents, and Orthents. 

Soil moisture regime dry to aquic. Major soil property featureless soil bodies. Diagnostic horizons typically absent, albic. Epipedon ochric. Characteristics little or no evidence of soil development. Description recently formed soils such as land surfaces that are very young (e.g., alluvium, colluvium, mudflows), extremely hard rocks, sandy parent material, disturbed material (e.g., mined land, highly compacted soils, or toxic material disposal). Exhibit A/C or A/R profiles. May have an Ap horizon. 

Ultisols Aquults Vegetation forest. Climate occur in any soil temperature regime. Soil moisture Udults regime precipitation greater than evapotranspiration, xeric to aquic. Major soil Ustults property low base saturation. Diagnostic horizons argillic, kandic, albic. 

Fluvisols (J) Other soils developed from recent alluvial deposits, having no diagnostic horizons other than (unless buried by 50 cm or more new material) an ochric or an umbric A horizon, an H horizon, or a sulfuric horizon ... 

Rankers (U) Other soils having an umbric A horizon which is not more than 25 cm thick having no other diagnostic horizons (unless buried by 50 cm or more of new material) ... 

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