Developed by
Department of Soil Science
University of Saskatchewan
51 Campus Drive, Saskatoon SK S7N 5A8

Orders: Organic

Soils of the Organic order are the dominant wetland soils found in forested regions of Canada (ORGANIC CANADA MAP). Their greatest extent is in the low-lying landscapes of the Hudson Plains ecozone but they occur in wetlands throughout the boreal forest. In the Prairie provinces they are commonly found immediately south of the contact between the sedimentary rocks of the southern Prairies and the Canadian Shield, whereas in Ontario and parts of Northern Quebec and Newfoundland and Labrador they occur on the Canadian Shield itself. Organic soils in these regions are commonly referred to as peats, bog or fen soils, or mucks. (Patterned Fen)

A second group of organic soils occurs in non-wetland positions in upland sites where leaf litter accumulates. In coastal B.C. they are found in the coastal rain forests where precipitation levels can reach 3000 mm per year, and great thicknesses of leaf litter and woody forest material accumulates. In other forested regions they are found where a layer of leaf litter directly overlies the bedrock surface.

The wetland variants of the Organic soils are associated with landscape positions where water accumulates and saturates the soil. In some sites the lack of an integrated river network causes runoff water accumulation in topographic low points. In other sites the groundwater table may be located at or near the mineral soil surface, and the soil profile is saturated with water for all or most of the year. The loss of dissolved oxygen in this stagnant water causes the soil to become anaerobic or anoxic. Ultimately the decomposition of any organic material added to the soil (both through roots and above-ground plant materials) becomes very slow or ceases altogether due to the inability of microorganisms to function in the anoxic conditions, and build-up of unaltered or partially decomposed organic matter begins at the soil surface. (Fibric Material) The thickness of the organic layer increases with time, and this process of organic matter accumulation (or paludification) is responsible for formation of Organic soils.

The degree of decomposition of the organic material in wetlands differs between sites and depends on the botanical origin of the wetland plant species, temperature, and the duration of water saturation and chemical composition of the water. Fibric material has undergone relatively little decomposition and most of the plant material can be readily identified as to its botanical origin. (Fibric Material) The other extreme is humic material, which is greatly decomposed and unrecognizable in origin. Mesic organic materials are intermediate between these two extremes. In the field these three stages are classified using the von Post scale of decomposition.

The master horizon for the wetland Organic soils is the O horizon. The three decomposition stages are assigned Of, Om, or Oh designations depending on the degree of decomposition of the organic material. The organic horizons must achieve a minimum thickness to be classified into the Organic order. (Depth Relationships) If the Organic horizons are less than these critical thicknesses, they are considered peaty phases of the Gleysolic order. If permafrost occurs at a depth less than 1 m from the organic soil surface, the soils are classified into the Cryosolic Order.

The upland versions of the Organic order are composed of leaf litter and other woody debris, which are termed folic materials. These organic horizons are assigned an L, F, or H designation, depending again on the degree of decomposition.

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