The Southern Plains

J. R. Johnston.

Complex interrelationships among climate, geology, soils, vegetation, and man have produced the geography of the region that includes the Southern High Plains, the Rolling Red Plains, the West Cross-timbers, the Blackland Prairies, and the Edwards Plateau.

The climate is semiarid to humid. Winters are extremely cold in places and mild elsewhere. The summers usually are hot and dry. The growing season is 180 days in the northern part to 300 days in the southern part. The topography varies from nearly level to strongly rolling. Surface drainage is well developed, except in the part of the region that is on the Southern High Plains in Texas. The soils range from slightly acid to calcareous and from deep sands and clays to thin soils.

The cultivated crops are cotton, grain sorghums, peanuts, wheat, corn, oats, barley, grass, and legume forages.

Cotton is the main cash crop, and growing it is a highly developed, mechanized enterprise in the Southern High Plains and Blackland Prairie of Texas.

Grain sorghum became a sizable cash and feed grain crop after combine and hybrid sorghums were developed. Wheat has been the leader in the Rolling Red Plains of Texas and Oklahoma.

Corn, oats, and barley are important in the Blackland Prairies. Forage sorghums are grown extensively for hay, silage, and bundle feed. Some alfalfa is grown in alluvial valleys and in places where water is plentiful for irrigation.

Much of the area is rangeland. The Edwards Plateau, the Rolling Red Plains, Crosstimbers, and Grand Prairie are predominantly rangeland. Buffalo, mesquite, gramas, bluestems, Indian, and tobosa grasses grow on them. Brush, mesquite, scrub oak, live oak, and post oak infest some rangeland.

THE SOILS in the High Plains are mainly the Amarillo, Brownfield, and Portales soils, which usually are red or reddish-brown and sandy in the surface. Some areas are loam and clay loam. The subsoils are red clay or sandy clay, blending at 2 to 5 feet into brown, buff, or yellow marl, which contains lime. These productive soils absorb moisture quickly, have good water-holding ability, and are easily worked. The sandier sections are subject to severe wind erosion if they are poorly managed.

Three large groups of soils occur in the Rolling Red Plains. The Miles-Vernon group ranges from sands to clays and are red, reddish-brown, or grayish-brown in the surface; red or reddish-brown subsoils have layers of lime accumulation. The St. Paul-Abilene group occurs only on relatively flat land and is generally of moderately fine texture in the surface and dark brown and fine textured in the subsoils. They are highly productive in seasons of good rainfall. The Zaneis-Renfrow group includes Reddish Prairie soils. In level areas they are deep; red or brown silt loam or very fine sandy loam surface mantles overlie red or brown clay or sandy clay subsoils. Large areas of these soils occupy sloping lands, where they are usually shallow.

The Crosstimbers area has predominantly Windthorst-Nimrod and associated soils. The Windthorst series is light colored in the surface and has red clay subsoils. The Nimrod series has sandy, light-colored surface soils over yellow, soft, pervious subsoils and is subject to severe wind erosion in the absence of plant cover.

The Valera-Ector association in the Edwards Plateau consists of shallow calcareous soils over limestone. They are light brown or dark, grayish brown in the surface and are associated with large areas of rough, stony land. This region, principally rangeland, is devoted to ranching with sheep, goats, and cattle.

The Grand Prairie has the San Saba-Denton group of soils, developed from limestone. Large areas lack definite profile development. The black San Saba series occurs mostly on flat land. The Denton soils are brown and shallow. The Crawford series is red.

The Blackland Prairie soils are not true Prairie soils but rather are like Rendzina, with calcareous profiles.

The Houston-Austin group is dominant in the area. The Houston series is dark, deep, calcareous, and highly productive. The Austin series is thinner, sometimes lighter colored, and less productive. These soils are subject to severe sheet and gully erosion. Wilson and Crockett soils occupy a strip on the east side of the Blackland Prairie. They are dark and noncalcareous over substrata of calcareous clay.

The Victoria-Goliad soils occur in the southern part of the region in the Rio Grande Plain. The Victoria series is dark brown or black and granular in the surface over grayish-brown clay subsoils. Goliad soils are black in the surface, with red or reddish-brown, crumbly, clay subsoils. Both are highly productive when moisture is adequate.

The Katy-Hockley soils have light-colored, more or less sandy surfaces over gray-mottled, rather dense, fine-textured subsoils. They are poorly drained, acid, low in organic matter, and low in natural productivity.