Folic Horizon of Island Soils in the Northern Part of the Sea of Okhotsk: Diagnostics, Genesis, Classification Position

Abstract The properties of folic, or dry-peat horizons (TJ in the Russian soil classification) in soils on mountainous islands in the northern part of the Sea of Okhotsk are considered, as well as their position in the system of organic horizons, and the dependence of their properties on soil-forming factors. The soils are formed on granodiorites under Pinus pumila low shrubs, grass-forb meadows, and dwarf-shrub tundra, primarily qualified for the dry-peat soils and dry-peat lithozem types (Folic Histosols, Folic Leptosols). The dry-peat horizon has the following average properties: a thickness of 30 cm, pHwater 4.9 and a high loss on ignition. Its main feature is a pronounced vertical stratification into subhorizons indicated as OJL, OJF, OLH, differing in the degree of plant residues decomposition and in the proportion of mineral material and collomorphic organic matter. The OJF subhorizon is the thickest (16.8 cm), whereas the OJL subhorizon is the thinnest (8.9 cm). The thickness of the subhorizons depends on the amount of incoming plant falloff and on moisture conditions. The thickness of the OJL subhorizon is mainly controlled by the environmental factors, whereas that of the OJH largely depends on pedogenic processes; the OJF subhorizon occupies an intermediate position. Some properties of the TJ horizon are similar to those of the litter-falloff O horizon. However, the TJ horizon is thicker and occupies a specific ecological niche: Subarctic meadows and mountains of Northeastern Russia. It is proposed to include soils with a TJ (folic) horizon into the orders of organo-accumulative and volcanic soils in the Russian soil classification system.