Fibrisol (F)

Soils of this great group are composed largely of relatively undecomposed fibric organic material. Fibric material is usually classified on the von Post scale of decomposition as classes 1-4. Fibrisols occur extensively in Canada, particularly in peat deposits dominated by sphagnum mosses.

Fibrisols have a dominantly fibric middle tier, or middle and surface tiers if a terric, lithic, or hydric contact occurs in the middle tier. Fibric material is the least decomposed type of organic material. It contains large amounts of well-preserved fiber that is retained on a 100-mesh sieve (0.15 mm) and can be identified as to botanical origin. A fibric horizon has 40% or more of rubbed fiber by volume and a pyrophosphate index of 5 or more (see Chapter 2, Organic horizons, Of). If the rubbed fiber volume is 75% or more, the pyrophosphate criterion does not apply. Dominantly fibric means that fibric material is the most abundant type of organic material. If both fibric and mesic layers occur in the middle tier, the tier is dominantly fibric if more than half of its thickness is composed of fibric material. If fibric, mesic, and humic layers are present in the middle tier, it is dominantly fibric if the thickness of fibric layers is greater than that of either mesic or humic layers. Subdominant in the following definitions means next in abundance to the dominant material but the layer must not be less than 12 cm in thickness if sharply contrasting (Of vs. Oh), or 25 cm in thickness if not sharply contrasting (Om vs. Of or Oh).

Typic Fibrisol (TY.F)

Common horizon sequence: Of or Om, Of

Soils of this subgroup have the general properties specified for the Organic order and the Fibrisol great group. They are composed mainly of fibric material that is commonly derived mainly from mosses.

These soils are identified by the following properties:

  1. If present, the middle and bottom tiers are dominantly fibric. A lithic contact may occur.
  2. They have neither subdominant humic layers with a total thickness of greater than 12 cm or subdominant mesic layers with a total thickness greater than 25 cm in the middle and bottom tier, or in the middle and surface tiers if a lithic contact occurs in the middle tier.
  3. The middle tier lacks terric, hydric, cumulic, and limnic layers.

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Mesic Fibrisol (ME.F)

Common horizon sequence: Of or Om, Of, Om, Of

Soils of this subgroup have the general properties specified for the Organic order and the Fibrisol great group. They differ from Typic Fibrisols by having a subdominant mesic layer (thicker than 25 cm) in the middle or bottom tier. The control section lacks terric, hydric, cumulic, or limnic layers.

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Humic Fibrisol (HU.F)

Common horizon sequence: Of, Om or Oh, Of, Oh, Of or Om

Soils of this subgroup have the general properties specified for the Organic order and the Fibrisol great group. They differ from Typic Fibrisols by having a subdominant humic layer thicker than 12 cm in the middle or bottom tier. They may also have a subdominant mesic layer. The control section lacks terric, hydric, cumulic, and limnic layers.

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Limnic Fibrisol (LM.F)

Common horizon sequence: Of or Om, Of, Oco

Soils of this subgroup have the general properties specified for the Organic order and the Fibrisol great group. They differ from Typic Fibrisols by having a limnic layer beneath the surface tier. A limnic layer is a layer or layers at least 5 cm thick of coprogenous earth (sedimentary peat), diatomaceous earth, or marl. Limnic materials include both organic and inorganic materials either deposited in water by precipitation or by the action of aquatic organisms such as algae and including diatoms, or derived from underwater and floating aquatic plants subsequently modified by aquatic animals. Except for some of the coprogenous earths, most of these limnic materials are inorganic. Diatomaceous earth is highly siliceous and marl is mainly CaCO3. Limnic Fibrisols may have mesic, humic, or cumulic layers but do not have terric or hydric layers.

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Cumulic Fibrisol (CU.F)

Common horizon sequence: Of or Om, Of, C, Of

Soils of this subgroup have the general properties specified for the Organic order and the Fibrisol great group. They differ from Typic Fibrisols by having a cumulic layer beneath the surface tier. They may have mesic or humic layers but lack terric, hydric, and limnic layers. A cumulic layer consists either of multiple layers of mineral material (alluvium) that together are more than 5 cm thick, or of one layer 5-30 cm thick.

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Terric Fibrisol (T.F)

Common horizon sequence: Of or Om, Of, C

Soils of this subgroup have the general properties specified for the Organic order and the Fibrisol great group. They differ from Typic Fibrisols by having a terric layer (an unconsolidated mineral layer at least 30 cm thick) beneath the surface tier. They may also have cumulic or limnic layers but do not have mesic, humic, or hydric layers within the control section.

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Terric Mesic Fibrisol (TME.F)

Common horizon sequence: Of or Om, Of, Om, C

Soils of this subgroup have the general properties specified for the Organic order and the Fibrisol great group. They differ from Typic Fibrisols by having both a terric layer beneath the surface tier and a subdominant mesic layer thicker than 25 cm in the control section. They may also have cumulic or limnic layers but lack humic and hydric layers.

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Terric Humic Fibrisol (THU.F)

Common horizon sequence: Of or Om, Of, Oh, C

Soils of this subgroup have the general properties specified for the Organic order and the Fibrisol great group. They differ from Typic Fibrisols by having both a terric layer beneath the surface tier and a subdominant humic layer thicker than 12 cm in the control section. They may also have mesic, cumulic, or limnic layers but lack a hydric layer.

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Hydric Fibrisol (HY.F)

Common horizon sequence: Of or Om, Of, W

Soils of this subgroup have the general properties specified for the Organic order and the Fibrisol great group. They differ from Typic Fibrisols by having a hydric layer (a layer of water that extends from a depth of not less than 40 cm to a depth of more than 1.6 m). They may also have mesic, humic, cumulic, terric, or limnic layers.

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Note: Diagnostic horizons are underlined.