Humisol (H)
Soils of this great group are at the most advanced stage of decomposition of the great groups of Organic soils. Most of the material is humified with few recognizable fibers. Humisols have a dominantly humic middle tier or middle and surface tiers if a terric, lithic, or hydric contact occurs in the middle tier. A humic layer is an organic layer having less than 10% rubbed fiber by volume and a pyrophosphate index of 3 or less. It has a higher bulk density, usually >0.195 Mg m-3, and a lower water-holding capacity than fibric or mesic layers. Humic material usually is classified on the von Post scale of decomposition as class 7 or higher and rarely in class 6.
Only minor areas of Humisols are known to occur in Canada.
Typic Humisol (TY.H)
Common horizon sequence: Om or Oh, Oh
Soils of this subgroup have the general properties specified for the Organic order and the Humisol great group. They are composed dominantly of well-decomposed organic materials. They are identified by the following properties:
- The middle and bottom tiers, if present, are dominantly humic. A lithic contact may occur.
- They do not have terric, hydric, cumulic, or limnic layers within the middle tier.
- They have neither subdominant fibric layers with a total thickness greater than 12 cm nor subdominant mesic layers with a total thickness greater than 25 cm in the middle or bottom tiers (or in the middle and surface tiers if a lithic contact occurs in the middle tier).
Fibric Humisol (FI.H)
Common horizon sequence: Om or Oh, Oh, Of, Oh
Soils of this subgroup have the general properties specified for the Organic order and Humisol great group. They differ from Typic Humisols by having a subdominant fibric layer thicker than 12 cm in the middle or bottom tiers. They may also have a subdominant mesic layer.
Mesic Humisol (ME.H)
Common horizon sequence: Om or Oh, Oh, Om, Oh
Soils of this subgroup have the general properties specified for the Organic order and the Humisol great group. They differ from Typic Humisols by having a subdominant mesic layer thicker than 25 cm in the middle or bottom tiers. They lack a subdominant fibric layer below the surface tier.
Limnic Humisol (LM.H)
Common horizon sequence: Om or Oh, Oh, Oco, Oh
Soils of this subgroup have the general properties specified for the Organic order and the Humisol great group. They differ from Typic Humisols 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. They may also have fibric, mesic and cumulic layers but do not have terric or hydric layers.
Cumulic Humisol (CU.H)
Common horizon sequence: Om or Oh, Oh, C, Oh
Soils of this subgroup have the general properties specified for the Organic order and the Humisol great group. They differ from Typic Humisols by having a cumulic layer beneath the surface tier. Also they may have fibric or mesic 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.
Terric Humisol (T.H)
Common horizon sequence: Om or Oh, Oh, C, Oh
Soils of this subgroup have the general properties specified for the Organic order and the Humisol great group. They differ from Typic Humisols 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 fibric, mesic or hydric layers within the control section.
Terric Fibric Humisol (TFI.H)
Common horizon sequence: Of or Oh, Oh, Of, C, Oh
Soils of this subgroup have the general properties specified for the Organic order and the Humisol great group. They differ from Typic Humisols by having both a terric layer (an unconsolidated mineral layer at least 30 cm thick) beneath the surface tier and a subdominant fibric layer thicker than 12 cm within the control section. They may also have mesic, cumulic or limnic layers but lack a hydric layer.
Terric Mesic Humisol (TME.H)
Common horizon sequence: Om or Oh, Oh, Om, C, Oh
Soils of this subgroup have the general properties specified for the Organic order and the Humisol great group. They differ from Typic Humisols by having both a terric layer (an unconsolidated mineral layer at least 30 cm thick) beneath the surface tier and a subdominant mesic layer thicker than 25 cm within the control section. These soils may also have cumulic or limnic layers but lack a subdominant fibric or hydric layer.
Hydric Humisol (HY.H)
Common horizon sequence: Om or Oh, Oh, W
Soils of this subgroup have the general properties specified for the Organic order and the Humisol great group. They differ from Typic Humisols by having a hydric layer. These soils may also have fibric, mesic, humic, cumulic, terric, or limnic layers. A hydric layer is a layer of water that extends from a depth of not less than 40 cm to a depth of more than 160 cm.
Note: Diagnostic horizons are underlined.