Editing Ultisol (section)

{{short description|Soil type}}
{{redirect|Red clay|other terms|Red clay (disambiguation)|and|Red dirt (disambiguation)}}
{{Infobox soil
|name=Ultisol
|alternative_name=Red Clay Soil
|image=Ultisol.jpg
|image_size=250px
|image_caption=A Ultisol profile
|classification_system=[[USDA soil taxonomy]]
|profile=
|parent_material=
|process=[[weathering]]
|climate=[[tropical climate|tropical]], [[humid subtropical climate|humid subtropical]], [[oceanic climate|oceanic]]
}}

'''Ultisol''', commonly known as '''red clay soil''', is one of twelve soil orders in the [[USDA soil taxonomy|United States Department of Agriculture soil taxonomy]]. The word "Ultisol" is derived from "ultimate", because Ultisols were seen as the ultimate product of continuous [[weathering]] of minerals in a humid, temperate climate without new [[soil formation]] via [[glaciation]]. They are defined as mineral soils which contain no [[calcareous]] ([[Limestone|calcium carbonate]] containing) material anywhere within the soil, have less than 10% weatherable minerals in the extreme top layer of soil, and have less than 35% [[base (chemistry)|base]] saturation throughout the soil. Ultisols occur in humid temperate or tropical regions. While the term is usually applied to the red clay soils of the [[Southern United States]], Ultisols are also found in regions of Africa, Asia, Australia and South America.

In the [[World Reference Base for Soil Resources]] (WRB), most Ultisols are known as [[Acrisol]]s and [[Alisol]]s. Some belong to the [[Retisol]]s or to the [[Nitisol]]s. Aquults are typically [[Stagnosol]]s or [[Planosol]]s. Humults may be [[Umbrisol]]s.<ref>{{Cite web|url = http://www.fao.org/3/i3794en/I3794en.pdf|title = World Reference Base for Soil Resources 2014, Update 2015|author=IUSS Working Group WRB|year = 2015|publisher = World Soil Resources Reports 106, FAO, Rome}}</ref>