Soils profile development

Due to the spatial irregularity of the rains and the occurrence of lateral runoff concentrating additional water in (micro) depressions, soil profile development may vary quite considerably from one location to another in arid zones. This phenomenon might, to some extent, explain the occurrence of A-Bt-C profiles, e g., with clear clay illuviation features, at some isolated locations in desert zones. 

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. 

How the soil profile develops continuous or sporadic migration of ions, molecules, particles and aerosols. Water is the vehicle for transportational processes... 

Analysis of soil-profile development also is a potential tool for dating landslides. New soil profiles will begin to develop on disrupted landslide surfaces. If such surfaces can be identified, dating the newly developed soil profile will indicate the age of movement. 

A typical soil profile developed under moorland vegetation (for scale the knife is about 25 em long). 

There was a discrepancy between water salinity limits for the three locations, which may be attributed to factors related to difference in soil texture and stmcture. This affects soil infiltration capacity and water retention. These soil hydrologic characteristics influence salt development in the soil profile, which affects plant... 

The variations in SOC concentration and SOM 513C value with depth show both consistent tendencies for soil profiles with different elevations at the DHSBR. This was mainly attributed to the regular decomposition of SOM compartments with different turnover rates during soil development. 

PROFILE is a biogeochemical model developed specially to calculate the influence of acid depositions on soil as a part of an ecosystem. The sets of chemical and biogeochemical reactions implemented in this model are (1) soil solution equilibrium, (2) mineral weathering, (3) nitrification and (4) nutrient uptake. Other biogeochemical processes affect soil chemistry via boundary conditions. However, there are many important physical soil processes and site conditions such as convective transport of solutes through the soil profile, the almost total absence of radial water flux (down through the soil profile) in mountain soils, the absence of radial runoff from the profile in soils with permafrost, etc., which are not implemented in the model and have to be taken into account in other ways. 

Based on predicted weathering and erosion rates of the region, we estimate the profile to be several million years old. Because the soil has developed in situ, the topmost grains have reacted with water for the greatest extent of time. With depth, the total "lifetime" of the particles as soil decreases. This implies that the topmost quartz surfaces should be "reactively mature" (all fines removed, deep grown-together etch pits) and the bottom-most quartz surfaces should be "reactively young" (plentiful fines, fresh surfaces). ... 

Wetlands occur on the valley floors and the lower slopes. The soils vary widely with parent materials and other factors, bnt there are some general patterns. On the valley floors, slopes decrease from the top to the bottom and the age and texture of the deposits vary accordingly. Where deposition is most active, the soils are yonng and have little profile development. These are Entisols. But most soils in the valley bottoms show at least some profile development and are Inceptisols or Alfisols where there is a prononnced dry season. 

Entisols show no evidence of soil-forming processes leading to profile development Aquents (Gleysols, pt Fluvisols, pt) are formed in continuously or near-continuously wet environments Fluvents (Fluvisols, pt) in recent alluvium in areas that are frequently flooded by rivers depositing new sediment... 

A large variety of zeolite species crystallize from volcanic glasses under weathering conditions and several can be associated in the same sample. The process seems most pronounced for acid eruptive rocks (Hay, 1963 Iijima and Harada, 1969 Harada, t al., 1967) but does occur in basalts also (Hay and Iijima, 1970). In some African soil profiles, zeolites (analcite) are found to develop at the expense of montmorillonite and sodium carbonate their appearance is apparently a function of local drainage. They grow in more stagnant situations at the expense of montmorillonite (Frankart and Herbillon, 1970). 

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