Subdivisions of Master Horizons

The subdivision of a horizon is indicated by lower-case letters that are used to designate specific features. They are listed in alphabetical order in Table 14.4. 

V Plinthite This symbol is used in B and C horizons that are humus poor and iron rich. The material usually has reticulate mottling of reds, yellows, and gray colors. 

X Fragipan character. This symbol is used to designate genetically developed firmness, brittleness, or high bulk density in B or C horizons. No cementing agent is evident. 

Note Arabic numerals can be added as suffixes to the horizon designations to identify subdivisions within horizons. For example, Btl-Bt2-Bt3 indicated three subsamples of the Bt horizon. 

The accumulation of substances such as silica, iron, aluminum, carbonate, and other salts can result in cemented layers, which change the physical, chemical, and biological behavior of the soil. For example, a cemented layer retards percolation and restricts root activity. Furthermore, the availability of nutrients for plant growth is reduced, i.e., the cation exchange capacity is reduced. There are accumulations in the soil which show the enrichment of one substance and/or the depletion of another substance. This can be expressed by diagnostic subsurface horizons, which are listed in alphabetically order in Table 14.5. It should be stressed that some characteristics can be measured only in the laboratory and not in the field. 

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