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= Plinthosols = Plinthosol soil group includes soils that contain 'Plinthite', a soft, iron-rich (some cases also Mn-rich ) and humus-poor, mixture of kaolinitic red-mottled clay with quartz and other constituents. When plinthosols is exposed to repeated wetting and drying, it changes irreversibly to a hardpan or irregular aggregates. Plinthosol is one of the 30 soil groups in the classification systems of the Food and Agriculture Organization (FAO).

The World Reference Base for Plinthosols
The World Reference Base for Soil Resources (WRB) classified Plinthosols in the SET #6, and SET #6 holds the 'typical' red and yellow soils found mostly in the wet tropical and subtropical regions. The high temperature and high moisture in the soil facilitate the weathering of the rock and the rapid decay of soil organic matter. The soils in this group are often deep and genetically mature, with a long history of dissolution and transport of weathering products.

The World Reference Base for Soil Resources (WRB) listed the different names of Plinthosol soils in different countries, owing to their highly variable diagnostic features and taxonomic structure in different regions.

Brazil

 * Groundwater Laterite Soils, or
 * Perched Water Laterite Soils

France

 * Sols gris latéritiques

United States of America

 * Plinthaquox
 * Plinthaqualfs
 * Plinthoxeralfs
 * Plinthustalfs
 * Plinthaquults
 * Plinthohumults
 * Plinthudults, and
 * Plinthustults

Plinthite
The formation process of Plinthite normally takes place in moist (sub)soil layers, and involved two common processes :


 * 1) The discharge of dissolved weathering products, along with the advanced hydrolysis would result in the removal of silica and bases from the soil, and then lead to relative accumulation of the weathering resistant sesquioxides, quartz and kaolinite or the absolute accumulation of sesquioxide from outside enrichment.
 * 2) Alternating reduction and oxidation would result in the segregation of iron (shown as the red-mottles).

Petroplinthite
Petroplinthite is formed under the condition when the land becomes drier, the plinthite would hardens irreversibly to petroplinthite, and the formation involved two processes :

The hardening of the plinthites to petroplinthite is often triggered by the removal of the vegetation, as it initiates the erosion of the surface soil which expose the plinthite to the open air.
 * 1) Amorphous iron compounds is crystallized to continuous aggregates of iron oxide minerals, especially goethite
 * 2) Goethite (FeOOH) is dehydrated to hematite (Fe2O3) and, if present, of gibbsite (Al2O3.3H2O) to boemite (Al2O3.H2O).

Parent Material
Plinthite is more common in weathering material from basic rocks than from the acidic rocks. There are sufficient irons present inn the plinthite, either from the parent material itself or via seepage water from elsewhere.

Environment
Plinthosols with soft plinthite generally form under hot and humid climate with a short dry season and high annual precipitation.

Plinthite is commonly found in locations with fluctuating groundwater levels, ranging from flat to gradually sloping.

Petroplinthite-riched soils are abundant in the transition zone between rain forest and savannah, particularly in arid places that were originally much wetter, example locations include the Sahel, and southern Sudan.

Distribution
There are about 60 million ha of Plinthosols globally. The soft plinthite can be found in the eastern part of the Amazon basin, parts of the Southeast Asia, and the central Congo basin, and it mostly occurs under hot and wet climates. The hardened plinthite (petroplinthite) can be found in Sahel, India, and in drier parts of Southeast Asia and north Australia.

Plinthite
According to Blake et al., (2008), the plinthite can be identified by using the following criteria:
 * 1) When red mottles are moist, they are firm or very firm, and when the red mottles are dry, they are hard or very hard.
 * 2) They can be cut with a knife, but only with some effort.
 * 3) They barely stain the fingers when rubbed
 * 4) They do not slake when submerged in water.

Petroplinthite
Petroplinthite normally occurs as massive, continuous, iron enriched hardpans, or as discontinuous segregations, and it is formed where plinthite becomes exposed to the surface (The erosion surfaces that above the present drainage base).

Mineralogical characteristics
Both Plinthite and Petroplinthite have high contents of sesquioxides (hydrated Fe and Al oxide).

Physical characteristics
Soft plinthite is dense and impede the deep percolation of water and the penetration of the plant roots. In addition, the specific density of the petroplinthite increases with the increased iron content in the soil. Due to its low water storage capacity, and its dense characteristics, Plinthosols are not suitable for arable uses.

Chemical characteristics
Most Plinthosols have poor cation exchange capacity and low base saturation. All of the Plinthosols have high contents of iron and aluminium, and the composition may vary from more than 80% of iron oxides to about 40% iron oxides and 40% of aluminum oxide.

Management Practices
The Plinthosols in the bottomlands has low soil fertility caused by strong weathering, and might encounter water logging problems, which limits the arable farming and causes soil management problems.

Shallow, continuous petroplinthite could limit the rootable soil volume for water storage capacity and root penetration, which is unsuitable for arable uses, and can best be used for low volume grazing. In West Africa, soils with high contents of plinthite are still planted to food crops and tree crops, and these crops suffer from drought during the dry season. A variety of soil and water conservation strategies are therefore employed to improve soils for urban and peri-urban agriculture in the region.

Civil engineers have different perspectives on the Plinthosols than agronomists. Due to Plinthosols' high percentage of the iron oxide content, the hardened plinthite can be used as the subgrade material for roads or even iron ore. Massive petroplinthite can be used as a stable surface for building, and broken petroplinthites can be used in foundations or used to building blocks.