Description of Processes

This chapter lists the most important processes responsible for soil formation in an alphabetical order.

Adsorption: It occurs when the attractive forces between the solid soil surface (adsorbent) and the solution component (adsorbate) overcomes both the attractive forces between the solution component and the soil solution (solvent), as well as any repulsive forces between the soil surface and the adsorbing species.

Aggregation: Particles held together in units of varying size and shape by physical, chemical, and biological sub-processes. Aggregates are separated from adjoining aggregates by surfaces of weakness.

Alkalization: Accumulation of Na ions; formation of a natric horizon.

Audification: Accumulation of H+ ions.

Carbonation (calcification): Accumulation of calcium carbonate; formation of calcic or petroclacic horizons.

Chelation: Forming complexes with metals by organic agents. The metals are trapped in a ring structure, which is very stable.

Compaction: The physical reduction of the air content resulting in an increased bulk density.

Cryoturbation: Mixing of soil by low temperatures, e.g. to disrupt horizons, to incorporate organic matter into lower horizons, and to orient stones.

Dealkalization (solodization): Movement of Na ions out of a section of the profile.

Decarbonation (decalcification): Movement of calcium carbonate out of a section of the profile.

Decomposition: The biochemical breakdown of mineral and organic material.

Dehydration: Loss of water reverting the compound to the original state.

Deposition is the sedimentation of transported material:

  • Accumulation of soil particles / colluvium
  • Accumulation of nutrients / increase of CEC
  • Relative enrichment of medium-sized particles

Desalinization: Movement of soluble salts out of a section of the profile.

Desilication: Movement of silica out of a section of the profile.

Diffusion (into and out of the soil): Air exchanges between the atmosphere and the soil under the effects of partial pressures of mass movement.

Disaggregation: Breaking down of aggregates.

Dispersion: The process where soil structural elements break down in water and separate into their constituents.

Eluviation: Movement of material out of a section of the soil profile (literally washing away of material); depletion of the material washed away (e.g. sequioxides, clay minerals, organic material)

Energy influx / outflux: Radiation absorption / reflection:

  • Soil temperature
  • Microbiological activity -> humification ,decomposition, mineralization
  • Evaporation
  • Soil moisture

Erosion is the transport of soil particles (and organic matter) by water or wind.

  • Raindrop impact causes breakdown of soil aggregates
  • Soil movement / removal of the A horizon
  • Smoothing or levelling of the soil surface
  • Loss of nutrients / decrease of CEC
  • Selective particle transport results in the relative enrichment of coarse and fine particles and depletion of medium-sized particles
  • Reduced infiltration / increase in surface runoff / reduced soil moisture
  • Sealing of the soil surface

Ferrugination: Development of brown, reddish brown, and reddish soil colors.

Flocculation: It is a process where the individual particles of clay are coagulated to form floccular aggregates.

Gleization: It involves the reduction of iron and its segregation into redoximorphic features, or its removal by leaching form the gleyed horizon; process occurring in poorly drained soil.

Humification: Formation of humus from raw organic materials.

Hydration: Absorption of water to form a new compound which differs only slightly from the original state

Hydrolysis: The replacement of cations in a mineral structure .by hydrogen ions from the soil solution.

Illuviation: Movement of material into a section of the soil profile (literally washing into or towards); accumulation of material washed into (e.g. sequioxides, clay minerals, organic material)

Induration: Hardening of a section of the profile produced in association with iron pans and plinthite, and with other cementing agents (Si or Ca).

Infiltration: The entry of water into the soil surface

  • Rainwater infiltrates in the soil with soluble and suspended matter.
  • Soil moisture

Interflow (Subsurface flow, through flow, seepage): Lateral subsurface flow.

Lessivage: Physical downward movement of clay minerals.

Leucinization (decoloration): Lightening the color in a section of the profile – formation of an albic horizon.

Melanization: Darkening the color of light-colored mineral initial unconsolidated material by mixture and accumulation of organic matter; formation of a mollic horizon due to incorporation of organic matter.

Mineralization: Release of minerals in various forms during the decomposition of organic matter.

Neutralization: Counteraction of the H+ ions.

Outflow: Loss of water from the pedosphere to the groundwater. Loss of water and soluble and suspended matter from the system, i.e. loss from the soil zone (unsaturated and saturated zone) into the groundwater.

Oxidation: Formation of an oxide or the release of electrons.

Pedoturbation: The churning and disruption of horizon formation by biological, physical and to some extent chemical activity, such as wetting and drying, swelling and contraction, freezing and thawing, root pressures, animal burrowing, activity of man.

Podzolization: Process by which sequioxides are translocated in a soil profile. The soluble ferrous iron forms ate the sites of eluviation, and the insoluble ferric iron forms at the point of illuviation. Podzolization is a soil forming process resulting in the genesis of Podzols.

Precipitation: Separation and deposition of a substance in a solid form from a solution.

Reduction: Loss of oxygen ions or acceptance of electrons.

Salinization: Accumulation of soluble salts such as chlorides and sulphates of Ca, Mg, Na, or K.

Silication: Accumulation of silica.

Solifluction: Slow flow of saturated soil on a permanent frozen soil (permafrost table).

Solution: Dissolving of minerals into solution (e.g. calcium carbonate into bicarbonate).

Surface crusting (soil sealing): A process which results in the formation of soil crusts on the soil surface, ranging in thickness from a few mm to perhaps as much as 3 cm, that is much mor compact, hard and brittle, when dry, than the material immediately beneath.

Surface runoff (overland flow): Discharge of rainwater over the surface of the land. Surface runoff is composed of unconcentrated and concentrated flow.

Suspension: The floating of dispersed particles in a medium like water. It is one of the states of particle transport of eroded sediments, especially for the smaller and lighter particles such as clay.

Synthesis: The biochemical formation of a new compound by combination of elements or constituents.

Upward movement: Movement of dissolved or suspended matter by capillarity.

Weathering: All physical and chemical changes produced in rocks, at or near the earth’s surface, by atmospheric agents.


Effects of Processes

Soils are three-dimensional bodiesthat are variable in time and space. The change of soil morphological features or soil attributes is due to processes acting continuously on soils. Processes do interact with each other, resulting in feedback reactions. For example, process x results in a soil environment that influences process y which results in a soil environment that influences process x. Soils are considered as a system or network in which interconnected processes form soil features. Because of the complexity of the soil system it is not possible to examine and describe each process and their cause effect relationships. But it is possible to filter dominant processes in a landscape and observe their soil morphological outcome.