Categories and Nomenclature of Soil Taxonomy, Biology tutorial

Categories and nomenclature of soil taxonomy I:

Nomenclature of Soil Taxonomy:

Nomenclature system is logical and conveys the great deal of information about nature of soils. The names of the categorization units are combinations of syllables, most of which are derived from Latin or Greek and are root words in numerous modern languages. As each part of the soil name conveys the concept of soil character or genesis, the name automatically explains the general type of soil being classified. For example, soils of order aridisols (from Latin aridus; dry, and solum, soil) are typically dry soils in arid regions. With this brief explanation of the nomenclature of soil taxonomy, the general nature of soils in each of the soil orders are explained below.

Soil Orders:

Each of the world's soils is allotted to one of 12 orders, largely on basis of soil properties which reflect the major course of development. The general knowledge of 12 soil orders is necessary for understanding nature and function of soils in different environments.

i) Alfisols:

Alfisols are formed in cool to hot humid areas, but also one found in semiarid tropics and Mediterranean climates. Most frequently, alfisols expand under native deciduous forests and grasslands.

Distribution and Use:

Alfisols inhabit approx 10% of the land area globally. Generally, alfisols are productive soils. Good hardwood forest growth and crop yield are favored.

ii) Andisols:

Andisols are generally formed on volcanic ash deposited in recent geological times. They are usually found near volcano source or in areas downward from volcano, where adequately thick layer of ash has been deposited in eruptions.

Distribution and Use:

Andisols are found in areas where important depths of volcanic ash and other ejecta have accumulated. Worldwide, they make up less than 1% of the soil area. Andisols are extensively cultivated in Japan, generating enough food to support very high population densities. Andisols also take place along the Rift Valley of Eastern Africa.

iii) Entisols:

Weakly developed mineral soils without natural horizons or with only the beginnings of such horizons belong to entisols order. Most have the ochricepipedon and a few have human-made anthropic or agricepipedons. Few have albic subsurface horizons. Soil productivity ranges from very high for certain entisols formed in recent alluvium to very low for forming in shifting sand or on steep rocky slopes.

Distribution and Use:

Worldwide, entisols occupy approx 16% of the total ice-free land area and are found under the broad variety of environmental conditions. Poorly drained and seasonally flooded entisols take place in major river valleys. Agricultural productivity of entisols differs greatly depending on their location and properties, with sufficient fertilization and the controlled water supply, some entisols are productive.

iv) Gelisols:

These are young soils with little profile development. Principal defining characteristic of these soils is presence of the permafrost layer (layer of material which remains at temperatures below 0oC for more than two consecutive years). In gelisols, permafrost layer lies within 100cm of soil surface, in some cases rocks forced to surface form rings or netlike patterns.

Distribution and Use:

Gelisols cover over 11 million km2 or 8.6% of earth's land area. Blanketed under snow and ice for much of the year, most gelisols support tundra vegetation of lichens, grasses, and low shrubs which grow during brief summers.

Categories and nomenclature of soil taxonomy II:

Nomenclature of Soil Taxonomy:

As yet there is no worldwide, unified classification scheme for soil. Since the birth of the modern discipline of soil science roughly 100 years ago, scientists in different countries have used many systems to organise the various types of soils into groups.

Soil Orders:

The suborder and great group names of the soil taxonomy provide increasing levels of detail. The suborder aqualf, for example, combines aqu from the Latin aqua, for "water," and alf from alfisol to describe wet soils. Using assorted roots and combining them in different ways, scientists describe soils in a highly specialised and specific language. Aeric fragiaqualfs, for example, are wet, well-developed soils with aerated surface layers and restrictive subsoils.

i) Inceptisols:

In inceptisols the beginning or inception of profile development is evident. Inceptisols show more significant profile development than entisols, but are defined to exclude soils with properties that characterize certain other soil orders. Thus soil with only slight profile development occurring in arid regions or containing permafrost or andic properties, are excluded from the inceptisols.

Distribution and Use:

Inceptisols are widely distributed throughout the world and constitute more than 9% of the world's land area. They are prominent in mountainous areas, especially in the tropics and low-land rice-growing areas of Asia.

ii) Histosols:

Histosols are soils that have undergone little profile development because of the anaerobic environment in which they form. The main process of soil formation in histosols is the accumulation of partially decomposed organic parent material.

Distribution and Use:

Histosols cover only about 1% of the world's land areas in cold, wet regions of Alaska, Canada, Finland and Russia. Some histosols make very productive farmlands.

iii) Vertisols:

Vertisols develop from limestone, basalt or other calcium and magnesium rich parent materials, and are found mostly in subhumid to semiarid environments in warm region, where the climate features dry periods of several months.

Distribution and Use:

Globally, vertisols comprise about 2.5% of the total land area. Large areas of vertisols are found in India, Ethiopia, the Sudan, and Northern and eastern Australia. Smaller areas occur in sub-Saharan Africa and in Mexico, Venezuela, Bolivia and Paraguay. Large areas of vertisols in the tropics can produce greatly increased yields of food crops with improved soil management practices.

iv) Mollisols:

Mollisols are formed by the accumulation of calcium-rich organic matter, largely from dense root/systems of grasses. This humus-rich surface horizon is often 60 to 80 cm in depth and high in calcium and magnesium. Mollisols in humid regions generally have higher organic matter and darker, thicker mollicepipedons than their lower-moistureregime counterparts.

Distribution and Use

The largest area of Mollisols in the world stretches from east to west across the heartlands of Kazakhstan, Ukraine and Russia. Mollisols are among the most productive soils, though some fertilisation is generally required.

v) Ultisols:

The processes involved in farming Ultisols are clay mineral weathering, translocation of clays to accumulate in an argillic or kandic horizon, and teaching of base-farming cautions from t he profile. Most ultisols have developed under moist conditions in warm to tropical climates.

Distribution and Use:

About 9% of the soil area in the world is classified in the ultisols order. Ultisols are not naturally as fertile as alfisols or mollisols, they respond well to good management, where adequate levels of fertilisers and lime are applied, ultisols are quite productive.

vi) Oxisols:

The oxisols are the moist highly weathered soils in the classification system. They form in hot climates with nearly year-round moist conditions; hence the native vegetation is generally thought to be tropical rain forest. However, some oxisols are found in areas which are today much drier than was the case when the soils were forming their oxic characteristics. The clay content of oxisols is generally high, but the clays are of the low-activity, nonsticky type.

Distribution and Use:

Oxisols are found on about 8% of the world's land, most occur in the tropics such as South America and Africa. They equally occur in large geographic areas, often associated with ultisols. The best use of oxisols, other than supporting rain forests, is the culture of mixed-canopy perennial crops, especially tree crops, which can restore the nutrient cycling system that characterised the soil.

Categories and nomenclature of soil taxonomy III:


Several suborders are indicative of the moisture regime or temperature regime under which soils are found. Therefore, soils formed under wet conditions usually are recognized under separate suborders (like Aquents, Aquerts and Aquepts), as being wet soils. To find out relationship between suborder names and soil characteristics, the formative elements for suborder names are recognized and their connotation given. Therefore, the ustolls are dry mollisols. Similarly soils in Udolls suborder (from the Latin udus, humid) are moist ultisols.

Great Groups:

The great groups are subdivisions of suborders. More than 300 great groups are recognized. They are stated largely by the presence or absence of diagnostic horizons and arrangements of those horizons.


Subgroups are subdivisions of the great groups. Over 2,000 subgroups are recognized. The central concept of the great group makes up one subgroup, termed Typic.

Therefore, typichapludolls subgroup typifies the hapludolls great group. A hapludoll with limited drainage would be categorized as the aquichapludoll. One with proof of intense earthworm activity would fall in vermichapludolls subgroup. Few intergrades may have properties in coming with other orders or with other great groups.


Within the subgroup, soils fall in the particular family, if at the specified depth, they have similar physical and chemical properties affecting growth of plant roots. Approx 8,000 families have been recognized. Criteria utilized comprise broad classes of particle size, mineralogy, cation exchange activity of clay, temperature, and depth of soil penetrable by roots. Terms like loamy, sandy and clayey are utilized to recognize broad particle size classes. Terms utilized to explain mineralogical classes comprise siliceous, smectitic, kaolibnitic, carbonatic and mixed.


The series category is the most detailed unit of the categorization system. It is the subdivision of the family, and each series is stated by the specific range of soil properties comprising mainly the kind, thickness, and arrangement of horizons. Features like a hardpan within the certain distance below the surface, the distinct zone of calcium carbonate accumulation at the certain depth, or striking color characteristics really help in series recognition.

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