Illuvial horizon

Argilluviation is the formation of an argillic illuviation horizon, as a result of translocation of clay from the surface soil to the depth of accumulation. It is the dominant process in the Alfisol order of soils. The process consists of three essential phases ... 

Mechanism (1) is particularly important in peat and other organic-rich sediments, where clay and metal complexes are present in very low amounts in relation to the humus component. A typical example of humic substances bound by polyvalent complexes (item 2) is the Spodosol. These soils have developed under climatic and biologic conditions that have resulted in the mobilization and transport of considerable amounts of iron, aluminum, and organic matter into the B horizon. This illuvial horizon is a rich source of fulvic acids, which are readily separated from the sesquioxides by mild extractants. 

Martin, A. E. and Reeve, R. (1958). Chemical studies of podzolic illuvial horizons. III. Titration curves of organic matter suspensions. J. Soil Sci. 9, 89-100. 

This soil pHF procedure is used to assess the presence of active aluminium. When immersed in a solution of NaF, active A1 adsorbs F ions with a consequent release of OH-, leading to higher pH values. High pH values in NaF are found in soils derived from volcanic ash and in illuvial horizons of podzolised soils (Fielders Perrott 1966). 

The natural radioactivity of soils depends particularly on the origin and composition of the parent rock, on the degree of weathering, and on the prevalent types of the soil formation process (particularly leaching). For example, the soils obtained by weathering of acid rocks contain higher amounts of radioactive elements as compared to those produced from basic rocks. Heavy soils contain higher amounts of radioactive elements than sandy soils. The distribution of radioactive isotopes in the soil profile is usually fairly uniform, and only in certain soils is it possible to observe an increased accumulation in illuvial horizons. 

Bhs, Bs — ferruginously coloured, humus-sesquioxide or sesquioxide illuvial horizon with an indistinct structure. 

The prevalent phenomenon is the podzol formation, which is due to a translocation of R2O3 in the complex fulvic acids in the downward direction without an essential migration of clay minerals. As a result of this, a depreciated elluvial horizon and an illuvial horizon enriched in humus and sesquioxides are obtained. 

MARTIN A.E. and REEVE R. 1957. Chemical studies on podzolic illuvial horizons. 1. The extraction of organic matter by organic chelating agents. Journal of Soil Science, , 268-285. 

The podzol profile samples were taken from the groundwater catchment areas from humus (A0) eluvial (A) and illuvial (B) horizons and the parent material (C). In coarse-grained sand areas the profile waspoorly developed and mainly 20 cm thick, the thickness in till areas ranged from 40 to 80 cm. 

B Subsoil horizon that shows evidence of weathering or illuviation... 

Genetic soil formed by the soil-forming processes. Horizons of illuviation, residual ... 

Fig. 1. Hypothetical soil profile chat has all principal horizons. Not all horizons shown are present in any given profile, but every profile has some of them. Terms used in diagram Eluviation is the downward movement of soluble or suspended material in a soil from the A horizon to the B horizon by groundwater percolation. The term refers especially, but not exclusively, lo the movement of colloids, whereas the term leaching refers lo the complete removal of soluble materials. Illuviation is the accumulation of soluble or suspended material in a lower soil horizon that was transported from an upper horizon by the process of eluviation. Gleying is soil mottling, caused by partial oxidation and reduction of its constituent ferric iron compounds, due to conditions of intermittent water saturation. Process is also called gleizalion (Adapted from USD A diagram)...

Heinonsalo, J., Jorgensen, K. S. Sen, R. (2001). Microcosm-based analyses of Scots pine seedling growth, ectomycorrhizal fungal community structure and bacterial carbon utilization profiles in boreal forest humus and underlying illuvial mineral horizons. ELMS Microbiology Ecology, 36, 73-84. 

Mineral horizons in which the main feature is loss of silicate clay, iron, aluminum, or some combination of these, leaving a concentration of sand and silt particles Horizons formed below A, E, or O horizons. Show one or more of the following (i) illuvial concentration of silicate clay (Bt), iron (Bs), humus (Bh), carbonates (Bk), gypsum (By), or silica (Bq) alone or in combination (ii) removal of carbonates (Bw) (iii) residual concentration of oxides (Bo) (iv) coatings of sesquioxides that make horizon higher in chroma or redder in hue (Bw) (v) brittleness (Bx) or (vi) gleying (Bg). 

B horizon - zone in which leached material is deposited (sometimes called the zone of illuviation)... 

Below the zone of leaching is a zone of illuviation, or zone of deposition, sometimes called the B horizon, in which dissolved organic matter and previously solubilized iron and aluminum are deposited. Deposition occurs when the organic acids and associated complexed metals are sorbed onto soil minerals or when the organic acid molecules themselves are mineralized by bacterial action, causing the previously complexed metals to precipitate. Beneath this depositional soil horizon is a relatively unweathered mineral material, often called the C horizon, or parent material, because it is the original material from which the soil profile developed. 

Illuvial. Pertaining to the deposition of dissolved or particulate soil material into one area or horizon of the soil from another. This material is transported by the process of eluviation. 

E - horizon of maximum eluviation of clay, iron, aluminum, and showing a concentration of resistant minerals, such as quartz. It is generally lighter in colour than the A horizon B - zones of accumulations or illuviation. Illuviation means wash into. This horizon represents the region of maximum accumulation of material such as Fe, Al, and silicate clays. In arid regions, CaC03, CaSO, or other salts may accumulate... 

B horizon. Soil layers where illuviation has taken place from above. This includes (1) illuvial concentrations of silicate clay, iron, aluminum, humus, carbonates, gypsum, or silica, alone or in combination (2) evidence of accumulation or removal of carbonates and (3) residual concentration of iron and aluminum oxides. 

B Horizons in which the dominant feature is one or more of the following an illuvial concentration... 

Argillic Formed by illuviation of clay generally a B horizon, where the accumulation of clay is denoted by a lower case t and illuviation argillans are usually observable unless there is evidence of stress cutans. Requirements to meet an argillic horizon are 1/10 as thick as all overlying horizons >1.2 times more clay than horizon above, or if eluvial layer <15% clay, then >3% more clay, or if eluvial layer >40% clay, then >8% more clay. 

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