A Planosol in the World Reference Base for Soil Resources[ Major Soils of the World. ISRIC Wageningen, The Netherlands, 2001] is a soil with a light-coloured, Soil texture, surface Soil horizon that shows signs of periodic water stagnation and abruptly overlies a dense, slowly permeable subsoil with significantly more clay than the surface horizon. In the US Soil Classification of 1938 used the name Planosols, whereas its successor, the USDA soil taxonomy, includes most Planosols in the Great Groups Albaqualfs, Albaquults and Argialbolls.
Occurrence
These soils are typically in seasonally waterlogged flat lands. They occur mainly in
Subtropics and temperate, semi-arid and subhumid regions. Planosols are formed mostly in clayey
Alluvium and
Colluvium deposits. Geological stratification and/or a pedogenetic process of destruction and removal of clay has resulted in the relatively coarse-textured, light-coloured surface soil abruptly overlying finer textured subsoil; impeded downward percolation of water causes temporarily reducing conditions with a stagnic colour pattern, at least close to the abrupt textural change.
Geography
Planosols cover an estimated 130 million hectares of the world. Major areas with Planosols occur in subtropical and temperate regions with clear alternation of wet and dry seasons, as in
South America (
Uruguay, northeastern
Argentina,
Paraguay, eastern
Bolivia, the Brazilian
pampa, the
Pantanal mato-grossense and northeastern Brazil),
Africa (
zone,
East Africa and
Southern Africa), the east of the United States of America,
Southeast Asia (
Bangladesh and
Thailand), and
Australia.
Ecology
Planosols in their natural state support a sparse grass vegetation, often with scattered
and
that have shallow
root systems that can cope with temporary waterlogging.
agriculture land use on is normally less intensive than that on most other soils under the same climate conditions. Vast areas of Planosols are used for extensive grazing. Wood production on Planosols is much lower than on other soils under the same conditions.
Agriculture
In the temperate zone these soils are mainly in grass or planted to
such as
wheat and
sugar beet. Yields are modest even on drained and deeply loosened soils. Root development on natural unmodified Planosols is hindered severely by oxygen deficiency in wet periods, dense subsoil and, in places, by
toxic levels of
Aluminium in the rootzone. Planosols in
Southeast Asia are widely planted with
paddy field rice. Other crops met with little success.
are needed for good yields. In climates with long dry periods and short infrequent wet spells the best land use are
. Strongly developed Planosols with a very
or
surface soil are best left untouched.
See also
-
IUSS Working Group WRB: World Reference Base for Soil Resources, fourth edition. International Union of Soil Sciences, Vienna 2022. ([2]).
Further reading
-
W. Zech, P. Schad, G. Hintermaier-Erhard: Soils of the World. Springer, Berlin 2022, Chapter 9.3.4.
External links
