The 1938 soil taxonomy divided soils into three orders dependent on dominant soil forming factors.

Intrazonal soils

Intrazonal soils have more or less well-defined

soil profile A soil horizon is a layer parallel to the soil surface whose physical, chemical and biological characteristics differ from the layers above and beneath. Horizons are defined in many cases by obvious physical features, mainly colour and texture. ...

characteristics that reflect the dominant influence of some resident factor of relief or

parent material Parent material is the underlying geological material (generally bedrock or a superficial or drift deposit) in which soil horizons form. Soils typically inherit a great deal of structure and minerals from their parent material, and, as such, are ...

over the classic zonal effects of climate and vegetation. There are three major sub-types, two of which have two further sub-types each. :Calcimorphic or

calcareous Calcareous () is an adjective meaning "mostly or partly composed of calcium carbonate", in other words, containing lime or being chalky. The term is used in a wide variety of scientific disciplines. In zoology ''Calcareous'' is used as an ad ...

soils develop from a

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms w ...

. It has two sub-types: ::

Rendzina Rendzina (or ''rendsina'') is a soil type recognized in various soil classification systems, including those of Britain and Germany as well as some obsolete systems. They are humus-rich shallow soils that are usually formed from carbonate- or occ ...

soils are thin soils with limited

available water capacity Available water capacity is the amount of water that can be stored in a soil profile and be available for growing crops. It is also known as available water content (AWC), profile available water (PAW) or total available water (TAW). The concept, p ...

. ::Terra rossa soils are deep red soils associated with higher rainfall than rendzina. :Hydromorphic soils form in

wetland A wetland is a distinct ecosystem that is flooded or saturated by water, either permanently (for years or decades) or seasonally (for weeks or months). Flooding results in oxygen-free (Anoxic waters, anoxic) processes prevailing, especially in t ...

conditions. There are two sub-types: ::

Gley soil A gleysol is a wetland soil ( hydric soil) that, unless drained, is saturated with groundwater for long enough to develop a characteristic colour pattern. The pattern is essentially made up of reddish, brownish, or yellowish colours at surfaces ...

s - These occur when the pore spaces between the grains become saturated with water and contain no air. This lack of oxygen leads to anaerobic conditions which reduce the iron in the parent rock. This gives the soil a characteristic grey/blue colour with flecks of red. ::

Peat Peat (), also known as turf (), is an accumulation of partially Decomposition, decayed vegetation or organic matter. It is unique to natural areas called peatlands, bogs, mires, Moorland, moors, or muskegs. The peatland ecosystem covers and ...

soils form under circumstances that prevent the breakdown of vegetation completely. :Halomorphic soils form due to

soil salination Soil salinity is the salt content in the soil; the process of increasing the salt content is known as salinization. Salts occur naturally within soils and water. Salination can be caused by natural processes such as mineral weathering or by the ...

Azonal soil

These soils are formed in mountainous regions out of fine grains produced by weathering. However, due to various reasons, this fine grained material constantly slides down the slope. As a result, the time necessary for the formation of soils does not become available. Therefore, these soils remain immature. An example is soil along the slopes of the Himalayan mountains. In river plains, particularly in flood-plain areas, new alluvium is deposited every year. The time for soil formation remains inadequate. Hence, flood plain soils also remain immature. In river plains, due to alluvium and availability of water, the farmlands are fertile but the soils remain immature.

References

* * {{soil type Soil in the United States

Taxonomy Taxonomy is the practice and science of categorization or classification. A taxonomy (or taxonomical classification) is a scheme of classification, especially a hierarchical classification, in which things are organized into groups or types. ...

Usda Soil Taxonomy, 1938 Soil science

Intrazonal soils

Azonal soil

See also

References