Page 36 - Soil Degradation, Conservation and Remediation

1.6 Classification of World Soils 21

Torrox: Torrox are the Oxisols of the arid region. They have an aridic (torric) soil

moisture regime. Torrox may become productive soils for a variety of crops if
water and fertilizers are applied. They occur mainly in Southern Africa, Hawaii,
and some areas of Australia.

Udox: Udox are well-drained Oxisols with a udic soil moisture regime. These soils

develop in humid areas. There is usually adequate rainfall in normal years to
allow for continuous crop growing. Udox occur mostly in South America and in
parts of Africa and Asia.
Ustox: Ustox are the Oxisols that have an ustic soil moisture regime. These soils
are found in semiarid and subhumid climates. There is at least 90 consecutive
dry days in normal years. Available soil moisture is then very low, and cropping
is not done in that time. One crop may be grown in the season when rainfall
occurs. Two crops may be grown with irrigation in some areas. Ustox occur
over a large portion of the interior of South America and in extensive areas of
Africa.

1.6.10 Spodosols

Spodosols typically form in coarse-textured parent materials and have a reddish-
brown spodic horizon beneath a light-colored E horizon. Sometimes there is a fra-

gipan or another sequum (a sequum is a couplet of an eluvial horizon above an
illuvial horizon, usually an E and an underlying B horizon) (Schaetzl and Anderson
2005 ); many soil profiles in humid regions have an E–B sequum. Those soils that

have two sequa are termed bisequal soils (Schaetzl 1996 ) that has an argillic
horizon below the spodic horizon. Some Spodosols have a placic horizon either on
or within a spodic horizon or on a fragipan. Some Spodosols have thicker layers
than a placic horizon that are cemented by spodic materials (humus–aluminum–clay
complex) and organic matter. The particle-size class is mostly sandy, sandy- skeletal,
coarse loamy, loamy skeletal, or coarse silty. Spodosols are most extensive in areas
of cool, humid, or perhumid climates. They may also form, however, to a limited
extent, in warm, humid tropical regions, where they occur mostly in areas of quartz-

rich sands with fluctuating groundwater table. Most Spodosols in cool temperate
regions are covered with coniferous or, less commonly, hardwood forests. Plenty of
Spodosols are found in boreal forest regions. Some have been cleared for agricul-
ture. Spodosols are naturally infertile, but some Spodosols may be made productive
by good management. Spodosols occupy 2.6 % of the global ice-free land surface.
(Spodosols are called Podzols in WRB system.) Spodosols have four suborders.
They are:
Aquods: Aquods are Spodosols that have an aquic soil moisture regime. They are

poorly drained soils with a water table at or near the surface for much of the year.
A wide variety of hydrophytic (water loving) plants, ranging from sphagnum in
cold areas to palms in the tropics, grow on these soils.