USA SOIL TAXONOMY.
There are some hierarchies of categories in the soil taxonomy, which are in form of levels. They have been arranged according to U.S. Soil taxonomy from highest category to the lowest category. The following are the hierarchy of categories in the U.S Soil taxonomy:-
Orders (12) soil development condition. There are ten orders differentiated on gross morphological features by the presence or absence of diagnostic horizons or feature which shows the dominant set of soil forming processes that have taken place. The ten orders are alfisols, andisols, aridisols, entisols, gelisols, histosols, inceptisols, mollisols, oxisols, spodosols, ultisols, vertisols.
Suborders (64) similarities in soil formation. It is the next level of generalization; it permits more statements to be made about a given soil. The suborder focuses on genetic homogeneity like wetness or other climatic factors. There are 47 suborders within the 10 orders. The name of suborders consists of two syllables. The first connotes the diagnostics properties; the second is the formative element from the soil order name.
Great groups (325) different between soil horizon. Then great group permits more specific statements about a given soil as it notes the arrangement of the soil horizons. A total of 230 great groups (140 of which occur in the tropics) have been defined for the 47 suborders. The name of the great group consists of the name of the suborder and a prefix suggesting diagnostic properties.
Subgroups (2400+) profile characteristics. These are subdivision of the great groups. The central concept of a great group makes up one group (Typic). Other subgroups may have characteristics that are intergrades between those of the central concept and those of the orders, suborders, or great groups. Extra gradation is used to identify critical properties common in soils in several orders, suborders, and great groups.
Family (7500+), families are found in soils with a subgroup having similar physical and chemical properties affecting their response to management and especially to the penetration of plant roots. Differences in texture, mineralogy, temperature, and soil depth are bases for family differentiation.
Series (19000) town and landscape feature where soil first recognized. Its differentiating characteristics are based primarily on the kind an arrangement of horizons, color, texture, structure, consistence, reaction of horizons, chemical, and mineralogical properties of the horizons.
The following are the simplified key to soil orders of the U.S.A Soil taxonomy:-
Alfisols, these develop in humid and sub humid climates, have average annual precipitation of 500-1300mm. They are frequently under forest vegetation. Their characteristic features are, clay accumulation in a B horizon, thick E horizon, available water much of the growing season, slightly too moderately acid.
Andisols, are soils with over 60% volcanic ejector (ash, cinder, pumice, basalt) with bulk densities below 900 kg/m3. Their characteristic features are; Dark A horizon, early-stage secondary minerals (allophane, imogolite, ferrihydrite clays), high adsorption and immobilization of phosphorus, very high cation exchange capacity.
Aridisols exist in dry climates. Characteristic features: horizons of lime or gypsum accumulation, salty layers, and B horizons.
Entisols have no profile development except a shallow marginal A horizon. Many recent river floodplains, volcanic ash deposits, unconsolidated deposits with horizons eroded away, and sands are Entisols.
Gelisols are soils that contain within 200cm of the ground surface the condition known as permafrost.
Histosols are organic soils (peat and mucks) consisting of variable depths of accumulated plant remains in bogs, marshes, and swamps.
Inceptisols, these occur especially in humid regions, have weak to moderated horizon development. Horizon development has been retarded because of cold climate, waterlogged soils, or lack of time for stronger development. Its characteristic feature; Texture has to be finer than loamy very fine sand.
Mollisols, these are frequently under grassland, but with some broadleaf forest-covered soils. Its characteristic features; Deep, dark A horizons, they may have B horizons and lime accumulation.
Oxisols, these are excessively weathered, whereas few original minerals are left unweathered. They develop only in tropical and subtropical climates. Their characteristic features; Often Oxisols are over 3m deep, have low fertility, have dominantly iron and aluminum clays, and are acid.
Spodosols are typically the sandy, leached soils of cold coniferous forests. Its characteristic features; O horizons, strongly acid profiles, well-leached E horizons, Bh or Bs horizons of accumulated organic material plus iron and aluminum oxides.
Ultisols are extensively weathered soils of tropical and subtropical climates. Its characteristic features; Thick A horizon, clay accumulation in a Bt, strongly acid.
Vertisols, these normally exist in temperate to tropical climate with distinct wet and dry seasons. They have a high content of clays that swell when wetted and show cracks when dry. Its characteristic features; deep self-mixed A horizon, top soil falls into cracks seasonally, gradually mixing the soil to the depth of the cracking.
There are some hierarchies of categories in the soil taxonomy, which are in form of levels. They have been arranged according to U.S. Soil taxonomy from highest category to the lowest category. The following are the hierarchy of categories in the U.S Soil taxonomy:-
Orders (12) soil development condition. There are ten orders differentiated on gross morphological features by the presence or absence of diagnostic horizons or feature which shows the dominant set of soil forming processes that have taken place. The ten orders are alfisols, andisols, aridisols, entisols, gelisols, histosols, inceptisols, mollisols, oxisols, spodosols, ultisols, vertisols.
Suborders (64) similarities in soil formation. It is the next level of generalization; it permits more statements to be made about a given soil. The suborder focuses on genetic homogeneity like wetness or other climatic factors. There are 47 suborders within the 10 orders. The name of suborders consists of two syllables. The first connotes the diagnostics properties; the second is the formative element from the soil order name.
Great groups (325) different between soil horizon. Then great group permits more specific statements about a given soil as it notes the arrangement of the soil horizons. A total of 230 great groups (140 of which occur in the tropics) have been defined for the 47 suborders. The name of the great group consists of the name of the suborder and a prefix suggesting diagnostic properties.
Subgroups (2400+) profile characteristics. These are subdivision of the great groups. The central concept of a great group makes up one group (Typic). Other subgroups may have characteristics that are intergrades between those of the central concept and those of the orders, suborders, or great groups. Extra gradation is used to identify critical properties common in soils in several orders, suborders, and great groups.
Family (7500+), families are found in soils with a subgroup having similar physical and chemical properties affecting their response to management and especially to the penetration of plant roots. Differences in texture, mineralogy, temperature, and soil depth are bases for family differentiation.
Series (19000) town and landscape feature where soil first recognized. Its differentiating characteristics are based primarily on the kind an arrangement of horizons, color, texture, structure, consistence, reaction of horizons, chemical, and mineralogical properties of the horizons.
The following are the simplified key to soil orders of the U.S.A Soil taxonomy:-
Alfisols, these develop in humid and sub humid climates, have average annual precipitation of 500-1300mm. They are frequently under forest vegetation. Their characteristic features are, clay accumulation in a B horizon, thick E horizon, available water much of the growing season, slightly too moderately acid.
Andisols, are soils with over 60% volcanic ejector (ash, cinder, pumice, basalt) with bulk densities below 900 kg/m3. Their characteristic features are; Dark A horizon, early-stage secondary minerals (allophane, imogolite, ferrihydrite clays), high adsorption and immobilization of phosphorus, very high cation exchange capacity.
Aridisols exist in dry climates. Characteristic features: horizons of lime or gypsum accumulation, salty layers, and B horizons.
Entisols have no profile development except a shallow marginal A horizon. Many recent river floodplains, volcanic ash deposits, unconsolidated deposits with horizons eroded away, and sands are Entisols.
Gelisols are soils that contain within 200cm of the ground surface the condition known as permafrost.
Histosols are organic soils (peat and mucks) consisting of variable depths of accumulated plant remains in bogs, marshes, and swamps.
Inceptisols, these occur especially in humid regions, have weak to moderated horizon development. Horizon development has been retarded because of cold climate, waterlogged soils, or lack of time for stronger development. Its characteristic feature; Texture has to be finer than loamy very fine sand.
Mollisols, these are frequently under grassland, but with some broadleaf forest-covered soils. Its characteristic features; Deep, dark A horizons, they may have B horizons and lime accumulation.
Oxisols, these are excessively weathered, whereas few original minerals are left unweathered. They develop only in tropical and subtropical climates. Their characteristic features; Often Oxisols are over 3m deep, have low fertility, have dominantly iron and aluminum clays, and are acid.
Spodosols are typically the sandy, leached soils of cold coniferous forests. Its characteristic features; O horizons, strongly acid profiles, well-leached E horizons, Bh or Bs horizons of accumulated organic material plus iron and aluminum oxides.
Ultisols are extensively weathered soils of tropical and subtropical climates. Its characteristic features; Thick A horizon, clay accumulation in a Bt, strongly acid.
Vertisols, these normally exist in temperate to tropical climate with distinct wet and dry seasons. They have a high content of clays that swell when wetted and show cracks when dry. Its characteristic features; deep self-mixed A horizon, top soil falls into cracks seasonally, gradually mixing the soil to the depth of the cracking.
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