Brown earth
Encyclopedia
Brown earth is a type of soil
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...

. Brown earths are mostly located between 35° and 55° north of the Equator
Equator
An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....

. The largest expanses cover western and central Europe, large areas of western and trans-Uralian 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...

, the east coast of America
East Coast of the United States
The East Coast of the United States, also known as the Eastern Seaboard, refers to the easternmost coastal states in the United States, which touch the Atlantic Ocean and stretch up to Canada. The term includes the U.S...

 and eastern Asia. Here, areas of brown earth soil types are found particularly in Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...

, the Koreas, China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...

, eastern 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...

 and New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...

. Brown earths cover 45% of the land in England
England
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...

 and 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...

. They are common in lowland areas (below 1,000 feet) on permeable parent material. The most common vegetation types are deciduous
Deciduous
Deciduous means "falling off at maturity" or "tending to fall off", and is typically used in reference to trees or shrubs that lose their leaves seasonally, and to the shedding of other plant structures such as petals after flowering or fruit when ripe...

 woodland and grassland. Due to the reasonable natural fertility of brown earths, large tracts of deciduous woodland have been cut down and the land is now used for farming. They are normally located in regions with a humid temperate climate. Rainfall totals are moderate, usually below 76 cm per year, and temperatures range from 4°C in the winter to 18°C in the summer. They are well-drained fertile soils with a pH of between 5.0 and 6.5.

Horizontal structure


They generally have three horizon
Horizon
The horizon is the apparent line that separates earth from sky, the line that divides all visible directions into two categories: those that intersect the Earth's surface, and those that do not. At many locations, the true horizon is obscured by trees, buildings, mountains, etc., and the resulting...

s: the A, B and C horizon. Horizon A is usually a brownish colour, and over 20 cm in depth. It is composed of mull humus (well decomposed alkaline organic matter) and mineral matter. It is biologically active with many soil organisms and plant roots mixing the mull humus with mineral particles. As a result, the boundary between the A and B horizons can be ill defined in unploughed examples. Horizon B is mostly composed of mineral matter which has been weathered from the parent material, but it often contains inclusions of more organic material carried in by organisms, especially earthworms. It is lighter in colour than the A horizon, and is often weakly illuviated (leached). Due to limited leaching only the more soluble bases are moved down through the profile. Horizon C is made up of the parent material, which is generally permeable and non- or slightly acidic, for example clay 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...

.

General relations in western Europe

Brown Earths are important, because they are permeable and usually easy to work throughout the year, so they are valued for agriculture. They also support a much wider range of forest trees than can be found on wetter land. They are freely drained soils with well-developed A and B horizons. They often develop over relatively permeable bedrock of some kind, but are also found over unconsolidated parent material
Parent material
In soil science, parent material is the underlying geological material in which soil horizons form...

s like river gravels. Some 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 :...

s include well-drained alluvial soils in the brown earths too.

Typically the Brown Earths have dark brown topsoils with loamy particle size-classes and good structure – especially under grassland. The B horizon lacks the grey colours and mottles characteristic 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. The rich colour is the result of iron compounds, mainly complex oxides which, like rust, have a reddish-brown colour. Some of these soils are, in fact, red. For example, in the UK reddish brown earths occur on the Old Red Sandstone
Old Red Sandstone
The Old Red Sandstone is a British rock formation of considerable importance to early paleontology. For convenience the short version of the term, 'ORS' is often used in literature on the subject.-Sedimentology:...

 (Devonian
Devonian
The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...

) and the New Red Sandstone
New Red Sandstone
The New Red Sandstone is a chiefly British geological term for the beds of red sandstone and associated rocks laid down throughout the Permian to the beginning of the Triassic that underlie the Jurassic Lias; the term distinguishes it from the Old Red Sandstone which is largely Devonian in...

 (Permian
Permian
The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...

), and are red because the rocks from which they formed are derived from strongly oxidised deposits that were laid down under desert conditions millions of years ago.

In long-cultivated soils the pH
PH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...

 in the topsoil tends to be higher (more alkaline) than in the subsoil as a result of the addition of lime over the years. In general, the wetter the climate, the more acidic the soils. This is because rain tends to wash the “alkaline” bases out of the soil. Of course, the parent material also has an effect, and hard acidic rocks give rise to more acidic soils than do the softer sandstones. The landscapes where these lowland soils occur are typically undulating, and interesting variations in the profiles relate to the slopes where they are found. We think, perhaps of soils as static and unchanging, but in fact they are never stationary. The processes of weathering and plant growth that were responsible for the formation of soils from bare parent materials in the first place are still going on. This is most easily seen on a hill slope. The top of the hill is usually convex, and it is here that most erosion is taking place – upper slopes and summits are more exposed to wind, and rain, and gravity is slowly but surely moving the topsoil down the hill. Thus soils on the brow of the hill tend to be shallower than those in mid-slope positions, where soil is moving down, but being replaced by material from above. At the base of the slope we usually find a concave area where the eroded soil has accumulated. Here the topsoils will be significantly thicker than elsewhere.

Classification

Brown earths have a long history of being a major grouping in most 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 :...

s. In France they have been included with "sol brun acide", although these soils may tend to have more iron and aluminium in the B horizon, and tend to what, in the British classification, is called a 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...

 soil. Brown earths are also classified in the German and Austrian soil taxonomy as "Braunerde." Braunerden are widespread and frequently occur on unconsolidated parent sand or loess parent materials. "Parabraunerde" is the classification for a brown earth with an elluvial horison above a slightly argillic, clayey illuvial horizon.
This gives rise to a universal division of these, generally brown and well drained soils into the weakly leached brown earths - called cambisols
Cambisols
A Cambisol in the FAO World Reference Base for Soil Resources is a soil with a beginning of soil formation. The horizon differentiation is weak...

 in the international 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...

 (WRB); and more leached 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 which there is an orange-brown B horizon, but no pale leached horizon between the A and the B horizons. These are called Umbrisols in the WRB, and are particularly common in western Europe, covering large areas in NW Spain.

Further east in Europe, in more continental climate
Continental climate
Continental climate is a climate characterized by important annual variation in temperature due to the lack of significant bodies of water nearby...

s, the soils show greater leaching of clay and other minerals, and are mapped as luvisols in the WRB. These are rather similar to brown earths, and some other classifications, including the British and French, call these soils argillic brown earths (sol brun lessive), because they have an argillic, i.e. clay-enriched horizon at some depth well below the A horizon. The argillic character is rather weakly expressed in the oceanic climate
Oceanic climate
An oceanic climate, also called marine west coast climate, maritime climate, Cascadian climate and British climate for Köppen climate classification Cfb and subtropical highland for Köppen Cfb or Cwb, is a type of climate typically found along the west coasts at the middle latitudes of some of the...

of the UK, and the differences between brown earths proper (cambic brown earths) and argillic yellow earths are not apparent to the general observer.
The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
x
OK