Soils with Plinthite - Soil Geography of the USA: A Diagnostic-Horizon Approach - page 298

Fig. 25.3 Counties containing soils with plinthite
25.5 Factors Influencing the Formation of Plinthite
In the USA plinthite occurs under narrow environmental conditions. All of the soil
series containing plinthite occur on loamy Coastal Plain sediments. In TX these
sediments are part of the Pliocene-aged Willis Formation. These materials are deep
to very deep and yield soils that are commonly moderately well-drained to well-
drained. The slopes range narrowly between 0 % and 8 %. The mean annual air
temperature for soils with plinthite is 19.4 C, and the mean annual precipitation is
1,300 mm. The vegetation includes southern pines, mixed pines, and broad-leaved
species, and in eastern TX grassland vegetation (Table 25.3 ).
25.6 Genesis of Plinthitic Soils
Gleization and ferrallitization are the dominant processes leading to the formation
of plinthite. Plinthite is a redoximorphic feature of many highly weathered soils and
is considered to be an iron-rich and humus-poor pedogenic product that hardens
irreversibly on exposure to sunlight (Aide et al. 2004 ). Distinct wet and dry seasons
may be important to the formation of plinthite (Anjos et al. 1995 ).