Pedogenesis
Encyclopedia
Pedogenesis is the science and study of the processes that lead to the formation of soil
(soil evolution) and first explored by the Russian geologist Vasily Dokuchaev (1846 – 1903), the so called grandfather of soil science, who determined that soil formed over time as a consequence of climatic, mineral and biological processes which he demonstrated using the soil forming equation:
In 1941 the Swiss scientist Hans Jenny (pedologist)
expanded Vasily Dokuchaev equation by adding relief/topology
as a factor and separating the biological processes into the fauna
and flora
coming up with the equation:
Pedogenesis is though more a parent than a branch of pedology
, whose other aspects include the soil morphology
, classification
(taxonomy
) of soils, and their distribution in nature, present and past (soil geography and paleopedology
).
The rate of chemical weathering
increases by 2-3 times when the temperature increases by 10 degrees Celsius.
Climate also affects which organisms are present, affecting the soil chemically and physically (movement of roots).
. Mixed or deciduous forests leave a larger layer of humus, changing the elements leeched and accumulated in the soil, forming alfisols
. Prairies have very high humus accumulation, creating a dark, thick A horizon
characteristic of mollisols
.
For example three species of land snails in the genus Euchondrus in the Negev desert are noted for eating lichens growing under the surface limestone
rocks and slabs (endolithic lichens). They disrupt and eat the limestone. Their grazing resulting in the weathering
of the stones, and the subsequent formation of soil. They have a significant effect on the region: the total population of snails is estimated to process between 0.7 and 1.1 metric ton per hectare per year of limestone in the Negev desert.
, lacustrine parent material and residual parent material, or bedrock.
Pedologists use the following generic functional relationship for understanding soil formation:
s = f (cl, o, r, p, t, ...)
where s - soil properties; cl - regional climate; o - potential biota; r - topography; p - parent material; t - time; ... - additional variables.
s.
Soil
Soil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics...
(soil evolution) and first explored by the Russian geologist Vasily Dokuchaev (1846 – 1903), the so called grandfather of soil science, who determined that soil formed over time as a consequence of climatic, mineral and biological processes which he demonstrated using the soil forming equation:
- Soil = f(C, PM, O) x time (where C = climate, PM = parent material, O = biological processes)
In 1941 the Swiss scientist Hans Jenny (pedologist)
Hans Jenny (pedologist)
Hans Jenny was a soil scientist and expert on pedology , particularly the processes of soil formation.- Overview :...
expanded Vasily Dokuchaev equation by adding relief/topology
Topology
Topology is a major area of mathematics concerned with properties that are preserved under continuous deformations of objects, such as deformations that involve stretching, but no tearing or gluing...
as a factor and separating the biological processes into the fauna
Fauna
Fauna or faunæ is all of the animal life of any particular region or time. The corresponding term for plants is flora.Zoologists and paleontologists use fauna to refer to a typical collection of animals found in a specific time or place, e.g. the "Sonoran Desert fauna" or the "Burgess shale fauna"...
and flora
Flora
Flora is the plant life occurring in a particular region or time, generally the naturally occurring or indigenous—native plant life. The corresponding term for animals is fauna.-Etymology:...
coming up with the equation:
- Soil = f(C, PM, R, O, V,) x time (where C = climate, PM = parent material, R = relief/topology, O = fauna, V = flora)
Pedogenesis is though more a parent than a branch of pedology
Pedology (soil study)
Pedology is the study of soils in their natural environment. It is one of two main branches of soil science, the other being edaphology...
, whose other aspects include the soil morphology
Soil morphology
Soil morphology is the field observable attributes of the soil within the various soil horizons and the description of the kind and arrangement of the horizons. C.F...
, classification
Soil classification
Soil classification deals with the systematic categorization of soils based on distinguishing characteristics as well as criteria that dictate choices in use.- Overview :...
(taxonomy
Taxonomy
Taxonomy is the science of identifying and naming species, and arranging them into a classification. The field of taxonomy, sometimes referred to as "biological taxonomy", revolves around the description and use of taxonomic units, known as taxa...
) of soils, and their distribution in nature, present and past (soil geography and paleopedology
Paleopedology
Paleopedology is the discipline that studies soils of past geological eras, from quite recent to the earliest periods of the Earth's history...
).
Climate
Climate regulates soil formation. Soils are more developed in areas with higher rainfall and more warmth.The rate of chemical weathering
Weathering
Weathering is the breaking down of rocks, soils and minerals as well as artificial materials through contact with the Earth's atmosphere, biota and waters...
increases by 2-3 times when the temperature increases by 10 degrees Celsius.
Climate also affects which organisms are present, affecting the soil chemically and physically (movement of roots).
Organisms
The organisms living in and on the soil form distinct soil types. Coniferous forests have acidic leaf litter and form what are known as inceptisolsInceptisols
Inceptisols are a soil order in USDA soil taxonomy. They form quickly through alteration of parent material. They are older than entisols. They have no accumulation of clays, Iron, Aluminum or organic matter. They have an Ochric or Umbric horizon and a cambic subsurface horizon....
. Mixed or deciduous forests leave a larger layer of humus, changing the elements leeched and accumulated in the soil, forming alfisols
Alfisols
Alfisols are a soil order in USDA soil taxonomy. Alfisols form in semiarid to humid areas, typically under a hardwood forest cover. They have a clay-enriched subsoil and relatively high native fertility. "Alf" refers to aluminium and iron . Because of their productivity and abundance, the...
. Prairies have very high humus accumulation, creating a dark, thick A horizon
Soil horizon
A soil horizon is a specific layer in the land area that is parallel to the soil surface and possesses physical characteristics which differ from the layers above and beneath. Horizon formation is a function of a range of geological, chemical, and biological processes and occurs over long time...
characteristic of mollisols
Mollisols
Mollisols are a soil order in USDA soil taxonomy. Mollisols form in semi-arid to semi-humid areas, typically under a grassland cover. They are most commonly found in the mid-latitudes, namely in North America, mostly east of the Rocky Mountains, in South America in Argentina and Brazil, and in...
.
For example three species of land snails in the genus Euchondrus in the Negev desert are noted for eating lichens growing under the surface limestone
Limestone
Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....
rocks and slabs (endolithic lichens). They disrupt and eat the limestone. Their grazing resulting in the weathering
Weathering
Weathering is the breaking down of rocks, soils and minerals as well as artificial materials through contact with the Earth's atmosphere, biota and waters...
of the stones, and the subsequent formation of soil. They have a significant effect on the region: the total population of snails is estimated to process between 0.7 and 1.1 metric ton per hectare per year of limestone in the Negev desert.
Parent Material
The rock from which soil is formed is called parent material. The main types are: aeolian, glacial till, glacial outwash, alluviumAlluvium
Alluvium is loose, unconsolidated soil or sediments, eroded, deposited, and reshaped by water in some form in a non-marine setting. Alluvium is typically made up of a variety of materials, including fine particles of silt and clay and larger particles of sand and gravel...
, lacustrine parent material and residual parent material, or bedrock.
Pedologists use the following generic functional relationship for understanding soil formation:
s = f (cl, o, r, p, t, ...)
where s - soil properties; cl - regional climate; o - potential biota; r - topography; p - parent material; t - time; ... - additional variables.
Examples
A variety of mechanisms contribute to soil formation, including siltation, erosion, overpressure and lakebed succession. A specific example of the evolution of soils in prehistoric lake beds is in the Makgadikgadi Pans of the Kalahari Desert, where change in an ancient river course led to millennia of salinity buildup and formation of calcretes and silcreteSilcrete
Silcrete is an indurated soil duricrust formed when silica is dissolved and resolidifies as a cement. It is a hard and resistant material, and though different in origin and nature, appears similar to quartzite...
s.
See also
- CLORPTClorptClorpt or Corpt is a mnemonic for Hans Jenny's famous state equation for soil formation:S = f* S is for soil,* cl represents climate,* o organisms including humans,* r relief,* p parent material, or lithology, and...
- Parent materialParent materialIn soil science, parent material is the underlying geological material in which soil horizons form...
- Soil horizonSoil horizonA soil horizon is a specific layer in the land area that is parallel to the soil surface and possesses physical characteristics which differ from the layers above and beneath. Horizon formation is a function of a range of geological, chemical, and biological processes and occurs over long time...
- Soil production functionSoil production functionSoil production function refers to the rate of bedrock weathering into soil as a function of soil thickness.A general model suggested that the rate of physical weathering of bedrock can be represented as an exponential decline with soil thickness:...
- TopographyTopographyTopography is the study of Earth's surface shape and features or those ofplanets, moons, and asteroids...