Podsol
Encyclopedia
Soil science
Soil science is the study of soil as a natural resource on the surface of the earth including soil formation, classification and mapping; physical, chemical, biological, and fertility properties of soils; and these properties in relation to the use and management of soils.Sometimes terms which...
, podzols (also known as podsols or Spodosols) are the typical soils of coniferous, or boreal forests. They are also the typical soils of eucalypt
Eucalypt
Eucalypts are woody plants belonging to three closely related genera:Eucalyptus, Corymbia and Angophora.In 1995 new evidence, largely genetic, indicated that some prominent Eucalyptus species were actually more closely related to Angophora than to the other eucalypts; they were split off into the...
forests and heathlands in southern Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
. The name is Russian
Russian language
Russian is a Slavic language used primarily in Russia, Belarus, Uzbekistan, Kazakhstan, Tajikistan and Kyrgyzstan. It is an unofficial but widely spoken language in Ukraine, Moldova, Latvia, Turkmenistan and Estonia and, to a lesser extent, the other countries that were once constituent republics...
for "under ash" (под/pod=under, зола/zola=ash) and likely refers to the common experience of Russian peasants of plowing up an apparent under-layer of ash (leached or E 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...
) during first plowing of a virgin soil of this type. These soils are found in areas that are wet and cold (for example in Northern Ontario
Ontario
Ontario is a province of Canada, located in east-central Canada. It is Canada's most populous province and second largest in total area. It is home to the nation's most populous city, Toronto, and the nation's capital, Ottawa....
or Russia
Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...
) and also in warm areas such as Florida
Florida
Florida is a state in the southeastern United States, located on the nation's Atlantic and Gulf coasts. It is bordered to the west by the Gulf of Mexico, to the north by Alabama and Georgia and to the east by the Atlantic Ocean. With a population of 18,801,310 as measured by the 2010 census, it...
where sandy soils have fluctuating water tables (humic variant of the northern podzol or Humod). An example of a warm-climate podzol is the Myakka fine sand, state soil of Florida.
Most Spodosols are poor soils for agriculture
Agriculture
Agriculture is the cultivation of animals, plants, fungi and other life forms for food, fiber, and other products used to sustain life. Agriculture was the key implement in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that nurtured the...
. Some of them are sandy and excessively drained. Others have shallow rooting zones and poor drainage due to subsoil cementation. Well-drained loam
Loam
Loam is soil composed of sand, silt, and clay in relatively even concentration . Loam soils generally contain more nutrients and humus than sandy soils, have better infiltration and drainage than silty soils, and are easier to till than clay soils...
y types can be very productive for crops if lime
Agricultural lime
Agricultural lime, also called aglime, agricultural limestone, garden lime or liming, is a soil additive made from pulverized limestone or chalk. The primary active component is calcium carbonate...
and fertilizer
Fertilizer
Fertilizer is any organic or inorganic material of natural or synthetic origin that is added to a soil to supply one or more plant nutrients essential to the growth of plants. A recent assessment found that about 40 to 60% of crop yields are attributable to commercial fertilizer use...
are used.
The E horizon, which is usually 4-8 cm thick, is low in Fe and Al oxides and humus. It is formed under moist, cool and acidic conditions, especially where the parent material, such as granite
Granite
Granite is a common and widely occurring type of intrusive, felsic, igneous rock. Granite usually has a medium- to coarse-grained texture. Occasionally some individual crystals are larger than the groundmass, in which case the texture is known as porphyritic. A granitic rock with a porphyritic...
or sandstone
Sandstone
Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...
, is rich in quartz
Quartz
Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...
. It is found under a layer of organic material in the process of decomposition
Decomposition
Decomposition is the process by which organic material is broken down into simpler forms of matter. The process is essential for recycling the finite matter that occupies physical space in the biome. Bodies of living organisms begin to decompose shortly after death...
, which is usually 5-10 cm thick. In the middle, there is often a thin layer of 0.5 to 1 cm. The bleached soil goes over into a red or redbrown horizon called rusty soil. The colour is strongest in the upper part, and change at a depth of 50 to 100 cm progressively to the part of the soil that is mainly not affected by processes; that is the parent material. The soil profiles are designated the letters A (topsoil
Topsoil
Topsoil is the upper, outermost layer of soil, usually the top to . It has the highest concentration of organic matter and microorganisms and is where most of the Earth's biological soil activity occurs.-Importance:...
), E (eluviated soil), B (subsoil
Subsoil
Subsoil, or substrata, is the layer of soil under the topsoil on the surface of the ground. The subsoil may include substances such as clay and/or sand that has only been partially broken down by air, sunlight, water, wind etc., to produce true soil...
) and C (parent material
Parent material
In soil science, parent material is the underlying geological material in which soil horizons form...
).
The main process in the formation of Spodosols is podzolisation. Podzolisation is a complex process (or number of sub-processes) in which organic material and soluble minerals (commonly iron and aluminium) are leached from the A and E horizons to the B horizon.
In podzols, translocation
Translocation
Translocation may refer to:* Chromosomal translocation, in genetics* Translocation in plants, transport of food or pesticides through phloem or xylem* Protein translocation or protein targeting, a process in protein biosynthesis...
has meant the eluviation of clay
Clay
Clay is a general term including many combinations of one or more clay minerals with traces of metal oxides and organic matter. Geologic clay deposits are mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure.- Formation :Clay minerals...
s, humic acids, iron, and other soluble constituents from the A and E horizons. These constituents may then accumulate to form a spodic illuvial horizon and in some cases a placic horizon or iron band. Podzolization
Podzolization
Podzolization is the comprehensive name for the process of mobilization and precipitation of dissolved organic matter, together with aluminum Al and iron Fe as they are leaching down from the A and E horizons to the B horizon . Through this process the overlying eluvial horizons are getting bleached...
occurs when severe leaching
Leaching (pedology)
In pedology, leaching is the loss of mineral and organic solutes due to percolation. It is a mechanism of soil formation. It is distinct from the soil forming process of eluviation, which is the loss of mineral and organic colloids. Leached and elluviated materials tend to be lost from topsoil and...
leaves the upper horizon virtually depleted of all soil constituents except quartz grains. Clay minerals in the A horizon decompose by reaction with humic acids and form soluble salts. The leached material from the A horizon is deposited in the B horizon as a humus-rich horizon band, a hard layer of sesquioxide
Sesquioxide
A sesquioxide is an oxide containing three atoms of oxygen with two atoms of another element. For example, aluminium oxide is a sesquioxide.Many sesquioxides contain the metal in the +3 oxidation state and the oxide ion, e.g., Al2O3, La2O3...
s or a combination of the two.
However, as conifers allelopathically
Allelopathy
Allelopathy is a biological phenomenon by which an organism produces one or more biochemicals that influence the growth, survival, and reproduction of other organisms. These biochemicals are known as allelochemicals and can have beneficial or detrimental effects on the target organisms...
reduce competition by producing a thick O horizon of mor (acidic and poisonous leaf litter that is slow to decompose), the primary form of plant-soil interactions is that of the conifers themselves. The acidic O horizon, along with rainfall patterns that are similar to that of the moister grassland
Grassland
Grasslands are areas where the vegetation is dominated by grasses and other herbaceous plants . However, sedge and rush families can also be found. Grasslands occur naturally on all continents except Antarctica...
s, also promotes the illuviation of oxides of aluminium and iron.
In some podzols, the E horizon is absent -- either masked by biological activity or obliterated by disturbance. Podzols with little or no E horizon development are often classified as Brown podzolic
Brown podzolic
Brown podzolic soils are a subdivision of the Podzolic soils in the British soil classification. Although classed with podzols because they have an iron-rich, or spodic horizon, they are, in fact intermediate between podzols and Brown earths...
soils.
In Western Europe podzols are developed on heathland, which is a construct of human interference, whereby the vegetation is maintained through grazing and burning. The soils may well have developed over the past 3000 years in response to vegetation and climatic changes. In some British moorland
Moorland
Moorland or moor is a type of habitat, in the temperate grasslands, savannas, and shrublands biome, found in upland areas, characterised by low-growing vegetation on acidic soils and heavy fog...
s with podzolic soils there are brown earths preserved under Bronze Age
Bronze Age
The Bronze Age is a period characterized by the use of copper and its alloy bronze as the chief hard materials in the manufacture of some implements and weapons. Chronologically, it stands between the Stone Age and Iron Age...
barrows.
Spodosols are rare as paleosols. Though they are known from as far back as the Carboniferous
Carboniferous
The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...
, there are few examples surviving from before the first Pleistocene
Pleistocene
The Pleistocene is the epoch from 2,588,000 to 11,700 years BP that spans the world's recent period of repeated glaciations. The name pleistocene is derived from the Greek and ....
glaciation, and some of these may not be true Spodosols.