Page 37 - Soil Degradation, Conservation and Remediation

22 1 Soil Resources and Soil Degradation

Cryods: Cryods are Spodosols that have a cryic soil temperature regime. They are
found in high latitude or high elevations. They are abundant in Alaska, in the
mountains of Washington and Oregon of the USA, and Canada. Natural vegeta-
tion is mostly coniferous forest or alpine tundra.
Humods: Humods are the relatively freely drained Spodosols that have a large accu-

mulation of organic carbon in the spodic horizon. These soils have developed
under coniferous forests, and in western Europe, commonly found in sandy
materials where heather (a shrubland characterized by open, low growing woody
vegetation) is dominant. In the tropics, most Humods have supported a rain
forest.
Orthods: Orthods are the relatively freely drained Spodosols that have a moderate

accumulation of organic carbon in the spodic horizon. They are most extensive
in the Northeastern USA and the Great Lakes States. Most Orthods are used as
forest or have been cleared and are used as cropland or pasture. Orthods are natu-
rally infertile, but they can be highly responsive to good management.

1.6.11 Ultisols

Ultisols are red to yellow soils that are quite acidic, often having a pH of less than
5, and that develop in humid tropical (some in temperate) areas under forest vegeta-
tion. They are highly weathered soils and have an argillic or a kandic horizon with
low base saturation, less than 35 % BSP (by summation of exchangeable bases).
The low base saturation status is mainly due to formation in parent material high in
silica but low in bases. In some soils, the low base status results from intense leach-
ing of parent material, while in others, a low base status and small quantities of
weatherable minerals were initial parent material characteristics. They may have
any soil temperature regime and any soil moisture regime except aridic. Leaching is
high and bases released by weathering usually are removed by leaching. The red
and yellow colors result from the accumulation of iron oxide which is highly insol-
uble in water. Kaolinite, gibbsite, and aluminum interlayered clays are common in
the clay fraction. Major nutrients, such as calcium and potassium, are typically

deficient in Ultisols. They are poorly fertile soils which may not be productive for
most crops without addition of lime and fertilizers. Ultisols occupy 8.5 % of the
global ice-free land surface. (The WRB equivalents of Ultisols are Acrisols, Alisols,
and Plinthosols.) Ultisols have five suborders. They are:

Aquults: Aquults are the Ultisols that have a water table at or near the surface for
much of the year. Aquults are found extensively on the coastal plains of the
USA, particularly on the Atlantic and Gulf of Mexico. Most of the soils are
forested.

Humults: Humults are freely drained Ultisols rich in organic matter (> 0.9 % or

more organic carbon in the upper 15 cm of the argillic or kandic horizon) of mid
or low latitudes. Rainforests are the usual natural vegetation.