Soil Horizon - Sub-horizon Suffixes and Labels

Sub-horizon Suffixes and Labels

In addition to the main descriptors above, several modifiers exist to add necessary detail to each horizon. Firstly, each major horizon may be divided into sub-horizons by the addition of a numerical subscript, based on minor shifts in colour or texture with increasing depth (e.g., B21, B22, B23 etc.). While this can add necessary depth to a field description, workers should bear in mind that excessive division of a soil profile into narrow sub-horizons should be avoided. Walking as little as ten metres in any direction and digging another hole can often reveal a very different profile in regards to the depth and thickness of each horizon. Over-precise description can be a waste of time, and as a rule of thumb, layers thinner than 5 cm (2 inches) or so are best described as pans or segregations within a horizon rather than as a distinct layer.

Suffixes describing particular physical features of a horizon may also be added. These vary considerably between countries, but a limited selection of common ones are listed here:

• b : buried horizon.
• c : presence of mineral concretions or nodules, perhaps of iron, aluminium, or manganese.
• d : root restricting layer.
• f : frozen soil (permafrost).
• g : a gleyed horizon.
• h : accumulation of organic matter.
• p : disturbed by ploughing or other tillage practices (A horizon only).
• r : weathered, digable bedrock.
• s : sesquioxide accumulation.
• w : weak development.
• x : fragipan.

The US system employs largely similar suffixes, with a few important differences. For instance, 'e' under the US system denotes a horizon containing "organic material of intermediate decomposition" rather than a bleached horizon. A full list of suffixes is available online as part of the USDA Soil Survey Manual.