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Red soil is a type of
soil Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former ...
that typically develops in warm, temperate, and humid climates and comprise approximately 13% of Earth's soils. It contains thin organic and organic-mineral layers of highly leached soil resting on a red layer of
alluvium Alluvium (from Latin ''alluvius'', from ''alluere'' 'to wash against') is loose clay, silt, sand, or gravel that has been deposited by running water in a stream bed, on a floodplain, in an alluvial fan or beach, or in similar settings. ...
. Red soils contain large amounts of
clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4). Clays develop plasticity when wet, due to a molecular film of water surrounding the clay pa ...
and are generally derived from the
weathering Weathering is the deterioration of rocks, soils and minerals as well as wood and artificial materials through contact with water, atmospheric gases, and biological organisms. Weathering occurs '' in situ'' (on site, with little or no movement ...
of ancient
crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macro ...
line and metamorphic rock. They are named after their rich red color, which can vary from reddish brown to reddish yellow as a result of their high
iron Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in ...
content. Red soil can be good or poor growing soil depending on how it is managed. It is usually low in nutrients and humus and can be difficult to cultivate due to its low
water holding capacity Field capacity is the amount of soil moisture or water content held in the soil after excess water has drained away and the rate of downward movement has decreased. This usually takes place 2–3 days after rain or irrigation in pervious soils of u ...
; however, the fertility of these soils can be optimized with liming and other farming techniques. Red soils are an important resource because they make up such a large portion of farmland on the earth. In countries such as China, India, and Greece where there are large amounts of red soil, understanding the soil's properties are crucial to successful
agriculture Agriculture or farming is the practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that enabled people ...
. Red soil properties can vary across regions and may require different management practices to achieve the best results.


Characteristics

Red soils include multiple soil types (e.g
ultisol Ultisols, commonly known as red clay soils, are one of twelve soil orders in the United States Department of Agriculture soil taxonomy. The word "Ultisol" is derived from "ultimate", because Ultisols were seen as the ultimate product of continu ...
s,
alfisol Alfisols are a soil order in USDA soil taxonomy. Alfisols form in semi-arid to humid areas, typically under a hardwood forest cover. They have a clay-enriched subsoil and relatively high native fertility. "Alf" refers to aluminium (Al) and iron ( ...
s,
oxisol Oxisols are a soil order in USDA soil taxonomy, best known for their occurrence in tropical rain forest within 25 degrees north and south of the Equator. In the World Reference Base for Soil Resources (WRB), they belong mainly to the ferralsols, ...
s) that are classified as red soil when they develop a distinct reddish color, which can vary from reddish brown to reddish yellow due to their high
iron Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in ...
content. In general, red soils possess some characteristics of a good growing soil . They are generally acidic soils, which can be positive for agriculture, but in this case often causes a lack of sufficient nutrients. These soils are also prone to frequent drought in drier regions.


Composition

Red soils are generally derived from the
weathering Weathering is the deterioration of rocks, soils and minerals as well as wood and artificial materials through contact with water, atmospheric gases, and biological organisms. Weathering occurs '' in situ'' (on site, with little or no movement ...
of
crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macro ...
line and metamorphic rock in areas of high rainfall. Red soil contains large amounts of
clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4). Clays develop plasticity when wet, due to a molecular film of water surrounding the clay pa ...
and thin organic and organic-mineral layers of highly leached soil resting on an
alluvium Alluvium (from Latin ''alluvius'', from ''alluere'' 'to wash against') is loose clay, silt, sand, or gravel that has been deposited by running water in a stream bed, on a floodplain, in an alluvial fan or beach, or in similar settings. ...
red layer. The composition and agricultural properties of red soil varies across regions. One type of red soil may be considered infertile in one region but nutrient-rich in another. There is not a singular composition that classifies all red soils.


Soil Fertility and Management Practices

Red soils are typically difficult for crop cultivation because high leaching leads to low
water holding capacity Field capacity is the amount of soil moisture or water content held in the soil after excess water has drained away and the rate of downward movement has decreased. This usually takes place 2–3 days after rain or irrigation in pervious soils of u ...
, low nutrients, low organic matter ( humus), and acidification. Fluctuations in the concentration of
iron Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in ...
within red soil are found to have significant implications on its fertility and growth properties. The fertility of red soils can be improved with various farming techniques.


Liming

The process of soil liming helps to raise the pH of acidic soils. Because red soils are generally acidic in nature, liming is a useful farming technique to allow crops that don't tolerate acidic environments to thrive in red soil. However, modern research suggests that liming may have long-term environmental consequences on the soil. The systematic overflow of water through the soil gets into the organic matter of relevant sophgate of the soil.


Nutrient Application

Red soils are often deficient in
nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
, which limits the growth properties of the large majority of red soil.
Phosphorus Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ea ...
and
potassium Potassium is the chemical element with the symbol K (from Neo-Latin '' kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmos ...
can also become limited after the land has been harvested repeatedly. Nutrient application techniques introduce more of these lacking nutrients to the soil and allow them to restore chemicals that had diminished over time.


Organic Matter

Another management practice that can be used to improve the fertility of red soil is incorporating greater organic matter into the soil. Some strategies employed to practice this include the use of organic manure, and establishing proper tillage systems for the land.


Crop Rotation

The rotation of crops grown in red soil can significantly help to limit some of the compositional issues mentioned previously. Crop rotation helps to increase the content of organic matter, minimize the nitrogen deficiency, and help avoid
pests PESTS was an anonymous American activist group formed in 1986 to critique racism, tokenism, and exclusion in the art world. PESTS produced newsletters, posters, and other print material highlighting examples of discrimination in gallery represent ...
that damage the crops.


Geography


Red Soil in China

Red soil resources are estimated to cover 102 million
hectare The hectare (; SI symbol: ha) is a non-SI metric unit of area equal to a square with 100- metre sides (1 hm2), or 10,000 m2, and is primarily used in the measurement of land. There are 100 hectares in one square kilometre. An acre i ...
(1,020,000 square kilometeres) of land in tropical and
subtropical The subtropical zones or subtropics are geographical and climate zones to the north and south of the tropics. Geographically part of the temperate zones of both hemispheres, they cover the middle latitudes from to approximately 35° north a ...
regions of China. The primary areas of distribution are
Hainan Hainan (, ; ) is the smallest and southernmost province of the People's Republic of China (PRC), consisting of various islands in the South China Sea. , the largest and most populous island in China,The island of Taiwan, which is slightly l ...
,
Guangdong Guangdong (, ), alternatively romanized as Canton or Kwangtung, is a coastal province in South China on the north shore of the South China Sea. The capital of the province is Guangzhou. With a population of 126.01 million (as of 2020 ...
, and
Yunnan Yunnan , () is a landlocked province in the southwest of the People's Republic of China. The province spans approximately and has a population of 48.3 million (as of 2018). The capital of the province is Kunming. The province borders the ...
among other agricultural regions.


Red Soil in Greece

Red soils in have a significant role in the agriculture in Greece as well. They fall into two groups: residual soil forming in place from parent rock, and soil forming in deep sedimentary deposits. The residual red soils in Greece tend to be less than a meter in depth and form on sloping hillsides. Like other red soils in the Mediterranean, they tend to form in limestone. The red soils that form in deep sediments are widespread in the lowlands of Greece, occurring on gently sloping terrain.
Taxonomically In biology, taxonomy () is the scientific study of naming, defining ( circumscribing) and classifying groups of biological organisms based on shared characteristics. Organisms are grouped into taxa (singular: taxon) and these groups are given ...
, the Greek red soils belong to Rhodoxeralfs (red
alfisol Alfisols are a soil order in USDA soil taxonomy. Alfisols form in semi-arid to humid areas, typically under a hardwood forest cover. They have a clay-enriched subsoil and relatively high native fertility. "Alf" refers to aluminium (Al) and iron ( ...
), Palexeralfs (well aged alfisols), Xerochrepts (xeric inceptisol), and Orthents.


Red Soil in India

Red soils denote the largest soil group of
India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area, the List of countries and dependencies by population, second-most populous ...
, covering an area of about 350,000 sq.km (10.6% of India's area) across the Peninsula. India is rich with red soils in their southern, eastern, and northern regions. There, the soil appears yellow in its hydrated form. This soil, also known as the omnibus group, have been developed over Archaean granite,
gneiss Gneiss ( ) is a common and widely distributed type of metamorphic rock. It is formed by high-temperature and high-pressure metamorphic processes acting on formations composed of igneous or sedimentary rocks. Gneiss forms at higher temperatures a ...
and other crystalline rocks, the sedimentaries of the Cuddapah and Vindhayan basins and mixed Dharwarian group of rocks. In the uplands of India, the red soils are thin, poor and gravelly, sandy, or stony and porous, light-colored soils on which food crops like bajra can be grown. In contrast, on the lower plains and valleys they are rich, deep, dark colored fertile loam which, under irrigation, can produce excellent crops like
cotton Cotton is a soft, fluffy staple fiber that grows in a boll, or protective case, around the seeds of the cotton plants of the genus '' Gossypium'' in the mallow family Malvaceae. The fiber is almost pure cellulose, and can contain minor pe ...
,
wheat Wheat is a grass widely cultivated for its seed, a cereal grain that is a worldwide staple food. The many species of wheat together make up the genus ''Triticum'' ; the most widely grown is common wheat (''T. aestivum''). The archaeologi ...
, pulses,
tobacco Tobacco is the common name of several plants in the genus '' Nicotiana'' of the family Solanaceae, and the general term for any product prepared from the cured leaves of these plants. More than 70 species of tobacco are known, but the ...
,
jowar ''Sorghum bicolor'', commonly called sorghum () and also known as great millet, broomcorn, guinea corn, durra, imphee, jowar, or milo, is a grass species cultivated for its grain, which is used for food for humans, animal feed, and ethanol produ ...
, linseed, millet, potatoes and fruits.


Red Soil in Canada

Prince Edward Island Prince Edward Island (PEI; ) is one of the thirteen provinces and territories of Canada. It is the smallest province in terms of land area and population, but the most densely populated. The island has several nicknames: "Garden of the Gulf", ...
is famous for its iron-rich red soil.


See also

*
Ultisol Ultisols, commonly known as red clay soils, are one of twelve soil orders in the United States Department of Agriculture soil taxonomy. The word "Ultisol" is derived from "ultimate", because Ultisols were seen as the ultimate product of continu ...
, or red clay soil * Latosol, or tropical red earth * Inceptisol, or a soil order


References

{{Authority control Types of soil Geology of India