Brown podzolic
Encyclopedia
Brown podzolic soil
s are a subdivision of the Podzol
ic 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 earth
s. They are common on hilly land in western Europe, in climates where precipitation
of more than about 900mm exceeds evapotranspiration
for a large part of the year, and summers are relatively cool. The result is that leaching
of the soil profile occurs; in which mobile chemicals are washed out of the topsoil, or A horizon
, and accumulate lower down, in the B horizon
.
These soils have large amounts (more than 5%) of organic carbon in the surface horizon, which is therefore dark in colour. In unploughed situations there may be a "mor" humus layer in which the surface organic matter is only weakly mixed with the mineral component. Unlike podzols proper, these soils have no continuous leached E horizon. This is because they are formed on slopes where, over long periods, the topsoil weathered from higher up the slope is continually being carried down the slope by the action of rain, gravity and faunal activity. This means that fresh supplies of iron and aluminium oxides (sesquioxide
s) are constantly being provided, and leaching ensures a net accumulation of these compounds in the B horizon, giving an orange-brown "rusty" colour which is very distinctive. The aluminum and ferric
iron compounds in the subsoil also tend to bind the soil particles together, giving a "pellety" fine structure to the soil, and improving permeability, so that despite being in relatively high rainfall areas, the soils do not have the grey colours or mottles of gley soil
s.
In the World Reference Base for Soil Resources
, these soils are called Umbrisols, and the Soil Atlas of Europe shows a preponderance of this kind of soil in north-west Spain. There is a tendency for the soils to occur in oceanic
areas, where there is abundant rainfall throughout the year, winters are mild and summers relatively cool. Thus they are common in Ireland
, Scotland
, Wales
(where they occupy about 20% of the country) and western England, especially Devon
, Cornwall
and the Lake District
. They also occur in the Appalachian Mountains
and on the west coast of North America
.
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...
s are a subdivision of the Podzol
Podsol
In soil science, podzols are the typical soils of coniferous, or boreal forests. They are also the typical soils of eucalypt forests and heathlands in southern Australia...
ic soils in the British soil 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 :...
. Although classed with podzols because they have an iron-rich, or spodic horizon, they are, in fact intermediate between podzols and Brown earth
Brown earth
Brown earth is a type of soil. Brown earths are mostly located between 35° and 55° north of the Equator. The largest expanses cover western and central Europe, large areas of western and trans-Uralian Russia, the east coast of America and eastern Asia. Here, areas of brown earth soil types are...
s. They are common on hilly land in western Europe, in climates where precipitation
Precipitation (meteorology)
In meteorology, precipitation In meteorology, precipitation In meteorology, precipitation (also known as one of the classes of hydrometeors, which are atmospheric water phenomena is any product of the condensation of atmospheric water vapor that falls under gravity. The main forms of precipitation...
of more than about 900mm exceeds evapotranspiration
Evapotranspiration
Evapotranspiration is a term used to describe the sum of evaporation and plant transpiration from the Earth's land surface to atmosphere. Evaporation accounts for the movement of water to the air from sources such as the soil, canopy interception, and waterbodies...
for a large part of the year, and summers are relatively cool. The result is that 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...
of the soil profile occurs; in which mobile chemicals are washed out of the topsoil, or 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...
, and accumulate lower down, in the B 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...
.
These soils have large amounts (more than 5%) of organic carbon in the surface horizon, which is therefore dark in colour. In unploughed situations there may be a "mor" humus layer in which the surface organic matter is only weakly mixed with the mineral component. Unlike podzols proper, these soils have no continuous leached E horizon. This is because they are formed on slopes where, over long periods, the topsoil weathered from higher up the slope is continually being carried down the slope by the action of rain, gravity and faunal activity. This means that fresh supplies of iron and aluminium oxides (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) are constantly being provided, and leaching ensures a net accumulation of these compounds in the B horizon, giving an orange-brown "rusty" colour which is very distinctive. The aluminum and ferric
Ferric
Ferric refers to iron-containing materials or compounds. In chemistry the term is reserved for iron with an oxidation number of +3, also denoted iron or Fe3+. On the other hand, ferrous refers to iron with oxidation number of +2, denoted iron or Fe2+...
iron compounds in the subsoil also tend to bind the soil particles together, giving a "pellety" fine structure to the soil, and improving permeability, so that despite being in relatively high rainfall areas, the soils do not have the grey colours or mottles of gley soil
Gley soil
Gley soil in soil science is a type of hydric soil which exhibits a greenish-blue-grey soil color due to wetland conditions. On exposure to the air, gley colors are transformed to a mottled pattern of reddish, yellow or orange patches. During gley soil formation , the oxygen supply in the soil...
s.
In the World Reference Base for Soil Resources
World Reference Base for Soil Resources
The World Reference Base for Soil Resources is the international standard taxonomic soil classification system endorsed by the International Union of Soil Sciences . It was developed by an international collaboration coordinated by the International Soil Reference and Information Centre and...
, these soils are called Umbrisols, and the Soil Atlas of Europe shows a preponderance of this kind of soil in north-west Spain. There is a tendency for the soils to occur in oceanic
Ocean
An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...
areas, where there is abundant rainfall throughout the year, winters are mild and summers relatively cool. Thus they are common in Ireland
Ireland
Ireland is an island to the northwest of continental Europe. It is the third-largest island in Europe and the twentieth-largest island on Earth...
, Scotland
Scotland
Scotland is a country that is part of the United Kingdom. Occupying the northern third of the island of Great Britain, it shares a border with England to the south and is bounded by the North Sea to the east, the Atlantic Ocean to the north and west, and the North Channel and Irish Sea to the...
, Wales
Wales
Wales is a country that is part of the United Kingdom and the island of Great Britain, bordered by England to its east and the Atlantic Ocean and Irish Sea to its west. It has a population of three million, and a total area of 20,779 km²...
(where they occupy about 20% of the country) and western England, especially Devon
Devon
Devon is a large county in southwestern England. The county is sometimes referred to as Devonshire, although the term is rarely used inside the county itself as the county has never been officially "shired", it often indicates a traditional or historical context.The county shares borders with...
, Cornwall
Cornwall
Cornwall is a unitary authority and ceremonial county of England, within the United Kingdom. It is bordered to the north and west by the Celtic Sea, to the south by the English Channel, and to the east by the county of Devon, over the River Tamar. Cornwall has a population of , and covers an area of...
and the Lake District
Lake District
The Lake District, also commonly known as The Lakes or Lakeland, is a mountainous region in North West England. A popular holiday destination, it is famous not only for its lakes and its mountains but also for its associations with the early 19th century poetry and writings of William Wordsworth...
. They also occur in the Appalachian Mountains
Appalachian Mountains
The Appalachian Mountains #Whether the stressed vowel is or ,#Whether the "ch" is pronounced as a fricative or an affricate , and#Whether the final vowel is the monophthong or the diphthong .), often called the Appalachians, are a system of mountains in eastern North America. The Appalachians...
and on the west coast of North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
.