Pedogenesis

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Pedogenesis (from the Greek: 'pedo- or pedon' meaning 'soil, earth' and genesis meaning 'origin, birth') is the science and study of the processes that lead to the formation of soil (soil evolution) [1] 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 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:

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, whose other aspects include the soil morphology, classification (taxonomy) of soils, and their distribution in nature, present and past (soil geography and paleopedology).

Contents

Climate

Climate regulates soil formation. Soils are more developed in areas with higher rainfall and more warmth. 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).

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 inceptisols. 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).[2] They disrupt and eat the limestone.[2] Their grazing resulting in the weathering of the stones, and the subsequent formation of soil.[2] 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.[2]

Parent material

The rock from which soil is formed is called parent material. The main types are: aeolian, glacial till, glacial outwash, alluvium, lacustrine parent material and residual parent material, or bedrock.

Pedologists use the following generic functional relationship for understanding soil formation:[3]

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 silcretes.[4]

See also

Notes

  1. ^ Stanley W. Buol, F.D. Hole and R.W. McCracken. 1997
  2. ^ a b c d Odling-Smee F. J., Laland K. N. & Feldman M. W. (2003). "Niche Construction: The Neglected Process in Evolution (MPB-37)". Princeton University Press. 468 pp. HTM, PDF. Chapter 1. page 7-8.
  3. ^ Hans Jenny. 1994
  4. ^ C. Michael Hogan. 2008

References