Oklahoma State Soil

Port Silt Loam

Port Silt Loam

(Fine-silty, mixed, superactive, thermic Cumulic Haplustolls)

Adopted on April 1, 1987.

The Oklahoma State Soil, Port Silt Loam, Cumulic haplustolls, was adopted on April 1, 1987.

The citizens of Oklahoma should have a keen awareness that soil is one of our most valuable natural resources. We could not survive and enjoy life as we know it, without soil. We get our food and much of our clothing and shelter from plants growing in the soil. Yet our actions since statehood show that we do not take very good care of this resource that is so important to the livelihood and well-being of our people - we let over 100 million tons of topsoil wash and blow away each year.

Oklahoma State Soil: Port Silt Loam

Port Silt Loam

Oklahoma has a variable climate and many different kinds of geologic materials across the state. Both of these factors and others greatly influence the formation of different kinds of soil. There are over 2,500 different kinds of soil in Oklahoma. Some soils are naturally fertile, yet others are very limited in productivity. No one individual soil occurs throughout every region of the state.

Facts About Port Silt Loam

  • Port Silt Loam occurs in more counties than any other soil
    (about one million acres in 33 counties).
  • Port Silt Loam is deep, welldrained, and highly productive, suited for a wide range of cropsincluding alfalfa, small grains, sorghums, cotton and other sown crops, as well as range, pasture and woodland.
  • Port soil is usually reddish in color, from dark brown to dark reddish brown. The color is derived from upland soil materials weathered from reddish sandstones, siltstones, and shales of the Permian Geologic Era.
  • When Port soils are undisturbed, they produce native vegetation including tall grasses with an overstory of pecan, walnut, bur oak, and
    cottonwood trees. This native condition offers very desirable wildlife habitat for most of Oklahoma's wildlife species.

How Port Silt Loam Was Named

Soils are often named after an early pioneer, town, county, community or stream in the vicinity where they are first found. The name "Port" comes from the small community of Port located in Washita County, Oklahoma. The name "silt loam" is the texture of the topsoil. This texture consists mostly of silt size particles (.05 to .002 mm), and when the moist soil is rubbed between the thumb and forefinger, it is loamy to the feel, thus the term silt loam


The Port series consist of very deep, well drained, moderately permeable flood plain soils that formed in calcareous loamy alluvium of Recent age. These nearly level to very gently sloping soils are on narrow flood plains in the Central Rolling Red Prairies (MLRA-80A) and the Central Rolling Red Prairies (MLRA 78C). Slopes range from 0 to 3 percent. Mean annual precipitation is 32 inches. Mean annual temperature is 63 degrees F.

TAXONOMIC CLASS: Fine-silty, mixed, superactive, thermic Cumulic Haplustolls

SERIES ESTABLISHED: Jackson County, Oklahoma; 1942.

Oklahoma House Joint Resolution No. 1014

A Joint Resolution designating Port Silt Loam
as the official soil of the State of Oklahoma.

WHEREAS, Oklahoma is a state with bountiful resources, a state of great aesthetic and economic diversity, and a state with highly productive land and people; and

WHEREAS, Oklahoma's social and economic development is closely tied to our natural resources; and

WHEREAS, the common thread which runs through the origins of our petroleum industry to our modern day agriculture is our soil; and

WHEREAS, the diversity and productivity which has made our state great is rooted in the soil resource; and

WHEREAS, Port Silt Loam soil is a highly productive soil which can support a wide variety of crops as well as range, pasture, woodlands and native wildlife; and

WHEREAS, Port Silt Loam occurs in more counties in Oklahoma than any other soil type.

Now, Therefore, be it resolved by the House of Representatives and the Senate of the 1st Session of the 41st Oklahoma Legislature:

Section 1. Port Silt Loam is hereby designated the official soil of the State of Oklahoma.

Approved April 1, 1987.

State Soils
State Soils
A state soil is a soil that has special significance to a particular state. Each state in the United States has selected a state soil, twenty of which have been legislatively established. These Official State Soils share the same level of distinction as official state flowers and birds.