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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 found particularly in Japan, Korea, China, eastern Australia and New Zealand. Brown earths cover 45% of the land in England and Wales. They are common in lowland areas (below 1,000 feet) on permeable parent material. The most common vegetation types are deciduous 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.
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 . 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 Great Britain reddish brown earths occur on the Old Red Sandstone (Devonian) and the New Red Sandstone (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 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.
Further east in Europe, in more continental climates, 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 of the UK, and the differences between brown earths proper (cambic brown earths) and argillic yellow earths are not apparent to the general observer.
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