1938 USDA soil taxonomy

Overview

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

Intrazonal soils

Intrazonal soils have more or less well-defined soil profile characteristics that reflect the dominant influence of some resident factor of relief or parent material over the classic zonal effects of climate and vegetation. There are 3 major sub-types, 2 of which have 2 further sub-types each.

Calcimorphic or calcareous soils develop from a limestone. It has two sub-types:
Rendzina soils are thin soils with limited available water capacity.
Terra Rossa soils are deep red soils associated with higher rainfall than Rendzina.
Hydromorphic soils form in wetland conditions. 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.
Peat soils form under circumstances that prevent the breakdown of vegetation completely.
Halomorphic soils form due to soil salination.

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

See also

References