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Soil Orders of Texas
The system for classifying soils, Soil Taxonomy, is used worldwide. The
highest level of Soil Taxonomy is the Soil Order. There are 12 recognized soil
orders in the world. Of these, the state of Texas has nine. There are more than
1,300 soil series in Texas, and each series is classified in one of these nine
soil orders.
The Dominant Soil Orders map represents the general distribution of seven of the
nine soil orders in Texas. Seven soil orders, Alfisols, Aridisols, Entisols,
Inceptisols, Mollisols, Ultisols, and Vertisols, are mapped extensively in the
state. The other two soil orders, Histosols and Spodosols, which are mapped in
the southeastern part of the state, are not shown on the map because they cover
relatively small areas. The soil orders not found in Texas are Andisols
(volcanic soils), Gelisols (frozen soils), and Oxisols (highly weathered
tropical soils).
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Alfisols The Duval series is an example of an Alfisol. Alfisols have a subsurface
accumulation of clay and have greater than or equal to 35 percent base
saturation. Duval soils occur in the Northern and Western Rio Grande Plain on
nearly level to gently sloping uplands. |
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Aridisols
The Upton series is an example of an Aridisol. Aridisols are the dry soils of
the deserts. They have horizons with accumulations of carbonates, gypsum, or
sodium chloride. Upton soils occur in the Trans-Pecos region on nearly level to
moderately sloping uplands. |
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Entisols
The Galveston series is an example of an Entisol. Entisols are soils with little
evidence of soil formation. Galveston soils occur on nearly level to strongly
sloping coastal terraces, dunes, and offshore barrier islands along the Texas
Gulf Coast. |
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Histosols
The Allemands series is an example of a Histosol. Histosols are composed almost
entirely of organic matter in all stages of decomposition. Allemands soils occur
in southeast Texas in the coastal freshwater marshes. Histosols are not mapped
extensively in Texas. |
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Inceptisols
The Weswood series is an example of an Inceptisol. Inceptisols are soils with
weakly developed subsurface horizons. These soils may be shallow to bedrock,
occur on steeply sloping land, or they may be very deep soils in areas subject
to intermittent flooding. Weswood soils occur along the flood plains of the
Brazos and Colorado Rivers in central Texas. |
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Mollisols
The Pullman series is an example of a Mollisol. Mollisols have a distinctive
dark colored surface horizon that is enriched with organic matter. They formed
under grassland and are naturally fertile. Pullman soils occur in the High
Plains on nearly level and very gently sloping uplands. |
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Spodosols
The Babco series is an example of a Spodosol. Spodosols are acid soils with a
subsurface accumulation of iron and organic matter. These soils generally form
under forests. Babco soils occur in the Flatwoods of southeast Texas. Spodosols
are not mapped extensively in Texas.
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UltisolsThe Bowie series is an example of an Ultisol. Ultisols are highly weathered
soils that have a subsurface horizon enriched with clay. They have less than 35
percent base saturation. Bowie soils occur in the East Texas Timberlands on
broad, very gently sloping to moderately sloping uplands. |
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VertisolsThe Houston Black series is an example of a Vertisol. Vertisols are
characterized by the presence of a mineral in the clay fraction called
smectite. This mineral swells markedly when moist and shrinks when dry.
Houston Black soils occur in the Blackland Prairie in the central part of the
state from Bonham south to San Antonio.
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MLRA Region 9 Office USDA-NRCS Temple, TX
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The
Soil Orders of Texas Poster (PDF; 153 KB)
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