- 1938 USDA soil taxonomy
The 1938 USDA soil taxonomy was a
soil classificationsystem adopted by the United States Department of Agriculture, now obsolete. The classification system used previously was developed and published in 1936by C.F. Marbut, who was chief of the U.S. Soil Survey at that time. A drastic modification, the 1938system was extensively revised in 1949and remained in use until 1965. See USDA soil taxonomyfor the current system.
The 1938 soil taxonomy divided soils between three orders dependent on dominant soil forming factors.
Zonal soils have well-defined
soil profilecharacteristics due to the influence of climate, organisms, and particularly, vegetation. Pedalfers and pedocals are subdivisions within the zonal soil order.
Intrazonal soils have more or less well-defined
soil profilecharacteristics that reflect the dominant influence of some resident factor of relief or parent materialover the classic zonal effects of climate and vegetation. There are 3 major sub-types, 2 of which have 2 further sub-types each.
calcareoussoils develop from a limestone. It has two sub-types::: Rendzinasoils are thin soils with limited available water capacity.::Terra Rossa soilss are deep red soils associated with higher rainfall than Rendzina.:Hydromorphic soils form in wetlandconditions. There are two sub-types::: Gley soils - 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.:: Peatsoils form under circumstances that prevent the break down of vegetation completely.:Halomorphic soils form due to soil salination.
Azonal soils are without well-developed characteristics due either to their youth or to some condition of relief or parent material which prevent soil development. Soils forming in recent
eolian, alluvialand colluvial deposits are azonal.
Red Mediterranean soil
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