Haplic Planosol profile near Abiy Addi in EthiopiaDistribution of PlanosolsSoil profile of a Eutric Planosol
A Planosol in the World Reference Base for Soil Resources[1] is a soil with a light-coloured, coarse-textured, surface horizon that shows signs of periodic water stagnation and abruptly overlies a dense, slowly permeablesubsoil 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 subtropical and temperate, semi-arid and subhumid regions. Planosols are formed mostly in clayey alluvial and colluvial 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.
Planosols in their natural state support a sparse grass vegetation, often with scattered shrubs and trees that have shallow root systems that can cope with temporary waterlogging. Agricultural 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 crops 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 Al in the rootzone. Planosols in Southeast Asia are widely planted with paddyrice. Other crops met with little success. Fertilizers are needed for good yields. In climates with long dry periods and short infrequent wet spells the best land use are grasslands. Strongly developed Planosols with a very silty or sandy surface soil are best left untouched.
IUSS Working Group WRB: World Reference Base for Soil Resources, fourth edition. International Union of Soil Sciences, Vienna 2022. ISBN979-8-9862451-1-9 ([1]).
Ana C. R. Lima; Willem. B. Hoogmoed; Eloy A. Pauletto; Luiz F. S. Pinto (2009). "Management Systems in Irrigated Rice Affect Physical and Chemical Soil Properties". Soil and Tillage Research. 103 (1): 92–97. doi:10.1016/j.still.2008.09.011.
Jia, Huibin (30 December 2002). "Improvement of an Extremely Hard Soil, Planosol". Journal of Environmental Science Laboratory (Hokkaido College, Senshu University). 9: 55–144. NAID110000971288.
Jia, Huibin (August 1995). "潜育白浆土硅酸盐粘土矿物组成" [Mineral composition of gleyed planosol and silicate clay soils]. Chinese Journal of Soil Science (in Chinese). 26 (4): 162–164.
