Landuse The Southern High Plains area includes portions of Colorado, Kansas, Oklahoma, New Mexico, and Texas for a total of 29.8 million acres (NRCS, 1996). This document will be restricted to those soils found in the southern region states of Oklahoma, which has 3.1 million acres, and Texas, which has 23.8 million acres. There are approximately 1 million acres of this major land resource area (MLRA) in Kansas and New Mexico with a very small amount of acreage in Colorado. The soils of MLRA 77 are some of the driest within the southern region and the land is used primarily for farming and ranching. Irrigation began in earnest in the 1950s and increased until the early 1970s. Since that time, irrigated acres have declined due to the cost of pumping water from the aquifer. The Southern High Plains grows corn, wheat, cotton, grain sorghum, and has some rangeland. The southern portion of the area is the largest single cotton-production region in the United States.
Elevation and Topography The Southern High Plains are found on the flat, steppe land east of the Rocky Mountain foothills. Because of the broad expanse of this flat plateau, this area was one of the first highly mechanized agricultural regions in the world. The plains gently slope from the northwest to the southeast and range in elevation from 800 to 2000 m above sea level. Deep sands are located in the western portions of the MLRA with occasional dunes running eastward. Slopes are gentle and often less than 3%. Steeper slopes are found along the Brazos, Canadian, and Cimarron rivers. A shaded relief map for this MLRA may be accessed through the internet at (http://fermi.jhuapl.edu/states/states.html).
Climate The area has a semiarid to subhumid climate. Precipitation ranges from 16 to 20 inches annually and occurs mainly from late May through early September. October through April are dry months with occasional snow events. As with any semiarid climatic region, precipitation events are extremely variable and annual amounts differ widely from year to year. Precipitation places most of these soils within the ustic moisture regime. The MLRA is separated into the thermic temperature regime south of the Canadian river and mesic temperature regime north of the Canadian River. Average temperature ranges from 55°F in the north to 63°F in the south. The areas north of the Canadian River have minimum January temperatures in the 18 to 22°F range while the areas below the Canadian River are 18 to 28°F. Maximum July temperatures north of the Canadian range from 92 to 95°F while those south of the Canadian River range from 92 to 96°F. As with the original description of the climatic regimes, this river generally separates the cotton (Gossypium hirsutum L.) growing areas in the south from the non-cotton growing areas north. Average freeze-free periods range from 130 days in the north to 220 days in the south.
Soils MLRA 77 is part of the Great Plains Province and consists of High Plains and Plains Border areas (Buol, 1973). STATSGO soils of this MLRA are provided in Fig. 1. It is bordered on the southeast by the Coastal Plains Providence and the west by the Pecos valley. It is formed from eolian sediments which become finer and darker towards the northeast (Seitlheko, 1975). Most of the soils are deep, fine and medium textured Ustolls and Ustalfs (USDA, 1981).
Soils north of the Canadian River are mesic while those south are thermic. Paleustolls, Argiustolls, Paleustalfs, and Hapustolls are found on the uplands. Calciustolls and Paleustolls dominate the ridges with shallow Calciorthhids, Paleorthids and Torriorthents on the steep slopes of the breaks. Haplustolls are on young valley floors with Pellusterts in the clayey playa lake basins. Paleustalfs, Haplargids, Ustipsamments, and Torripsamments comprise the deep sandy soils in the southwest (USDA, 1981).
Of the approximately 27 million acres of this MLRA in Oklahoma and Texas, those soils that have areal extent of more than 10,000 acres fall into six orders�Alfisols, Aridisols, Entisols, Inceptisols, Mollisols, and Vertisols. These soils (>10,000 acres) are listed by soil subgroup in Table 1.
Most of the predominant soils are in the order Alfisols or Mollisols. The other orders are represented by fewer than three soils per subgroup. Specific soil series descriptions may be found on the Iowa State World Wide Web at (http://www.statlab.iastate.edu/cgi-bin/osd/osdname.cgi). After that site is accessed, the series name may be entered for a complete soil description. Selected physical properties for these soils are presented in Table 2.
Within this document, we shall only discuss five of the major soils (>10,000 acres) within this MLRA�Acuff, Amarillo, Pullman, Randall, and Sherm. The Acuff (fine-loamy, mixed, superactive, thermic Aridic Paleustolls) and Amarillo (fine-loamy, mixed, thermic Aridic Paleustalfs) soils are typical of the sandy loam soils of the Southern High Plains. The Pullman (fine, mixed, superactive, thermic, Torrertic Paleustolls) and Sherm (fine, mixed mesic Torrertic Paleustolls) are typical of the clay loam soils of the Southern High Plains. Pullman is thermic clay loam soil, which occurs south of the Canadian River, while the Sherm is the mesic temperature regime soil found north of the Canadian River. An additional predominant soil in this MLRA that is comparable to the Pullman and Sherm is the Olton (fine, mixed superactive, thermic Aridic Paleustolls). This soil has recently been discussed by Unger and Pringle (1998), and will not be discussed in detail in this document. The Randall (fine, smectitic thermic Ustic Epiaquerts), the final soil to be discussed, forms the drainage basin for the upland soils mentioned above. This clay-textured soil serves as the run off catchment for the entire Southern High Plains and forms the playa basin which is the most unique geomorphic feature of the area. Currently, the Randall soil series is being modified with additional soil series being described. Understanding the soil-water relations of these five soils will define the water relations of the entire MLRA.
The distribution, importance, variability, and management of the Acuff soil has been discussed by Unger et al. (1993). This soil series has been mapped as a loam, clay loam, and sandy clay loam (Table 3) and is extensively used for row crops. The Acuff series occupies parts of 22 Southern High Plains counties in Texas and is used for both irrigated and dryland production. This soil occupies over 950,000 acres in Texas and ranges from 0.1 to 37% within these counties. Variability in average infiltration rate ranges from >0.75 in. hr-1 for loose, bulked soil with heavy residues to <0.04 in. hr-1 for severely compacted tillage pans (see Table 4). Volumetric water contents at -0.033MPa ranged from 15.2% to 27.4% within 11 Texas pedons. The volumetric water contents for the same pedons at -1.5MPa ranged from 8.2 to 18.8%. Detailed profile descriptions from Unger et al. (1993) are available here.
The Amarillo series is the alfisol companion to the Acuff Mollisol. Although the Amarillo soil is named after Amarillo, Texas which lies in the central part of this MLRA, the soil is generally found in the southern, sandier portion of the region. Four soil profiles for the Amarillo series are given here. Water retention data for these soils are given in Table 5.
The Pullman is probably one of most extensive row cropped soils in the United States. Unger and Pringle (1981) have described the distribution, importance, variability, and management of this soil which covers more than 3.8 million acres in Texas. The remainder of the area is associated with playa lake soils of which the Randall occupies the playa floor. Pullman soils are typically thought of as clay loam textured but have some inclusions of silty clay loam textures. The water infiltration rates (Table 6) were generally higher in the southwest portion of the region than in the northern part. The cumulative infiltration for 10 minutes ranged from 0.80 to 1.64 inches with a mean of 1.27 inches and a standard deviation of 0.28 inches. Twenty hour cumulative infiltration ranged from 3.18 to 4.9 inches with a mean value of 4.33 inches with a standard deviation of 0.58 inches (see Table 7). Calculated volumetric water contents (Unger and Pringle, 1981) ranged from 21.1% to 28.5% for -0.033MPa in the A horizons. Similar calculated values for the -1.5MPa potentials ranged from 13.3 to 18.7%. Detailed profile descriptions for the Pullman soil are presented here.
Prior to the adoption of Soil Taxonomy (USDA, 1975), the Pullman soil discussed above incorporated the Sherm soil which will now be discussed. The taxonomic distinction between these soils is found at the family level in which the Sherm is a "mesic" soil while the Pullman is "thermic." Unger and Pringle (1986) evaluated seven Sherm pedons under various tillage conditions (Tables 8 and 9). They reported 10 minute cumulative infiltration values to range from 0.38 to 2.04 inches . The mean for these infiltrations was 1.13 inches with a standard deviation of 0.42 inches. The least value (0.38) occurred in a wheel track furrow which had a thick crust. The greatest value (2.04 in.) occurred in loose surface following sweep tillage. Twenty hour cumulative infiltrations ranged from 1.41 to 15.66 inches with a mean of 6.64 and a standard deviation of 4.35 inches. The least infiltration (1.41 in.) occurred under a loose surface which had a tillage pan at 2 inches below the surface. The greatest infiltration occurred preplant with a loose surface and no crusting conditions. Calculated -0.033MPa water contents ranged from 29.5 to 40.7%. The median value was 36.1% with a mean value of 35.2% with a standard deviation of 4.26. Calculated -1.5MPa values ranged from 19.2 to 28.2%. Median value was 23.1% with a mean value of 23.5% and a standard deviation of 3.3. Detailed profile descriptions for the Sherm soil are presented here.
The final soil of this MLRA to be discussed in detail will be the playa lake soils comprised of the Randall clay. Playas, as depressional areas that create ephemeral lakes, are the most interesting topographic feature of this MLRA. There are approximately 27,000 playas on the Southern High Plains which serve as catchment basins for runoff from the upland soils previously discussed. Most of MLRA 77 has no rivers or streams to remove runoff waters which flow to the internally drained playas. Playa lakes range in surface area from 0.5 to 25 ha and drain an area of approximately 300 ha. Prior to 1985, all playas were classified as Randall except those playas in the mesic temperature regime, which were classified as Ness (Fine, smectitic, mesic Udic Pellusterts). Playas that were found under more arid conditions were classified as Lipan (Fine, smectitic thermic Chromic Haplusterts). Four typical Randall soil profiles are presented here (Evans, 1990; Paetzold, 1972). Water retention data from two Randall soil profiles at several depths are presented in Table 10.
Historically, the playas have been thought to lose most of their accumulated water back to the atmosphere by evaporation (Reddell, 1965). Recent investigations (Zartman et al., 1994) have revealed large quantities of recharge occurring from playa lakes. They evaluated three playa lakes at different elevations with in each lake. Each of the three polypedons was divided further into one of three classes of elevations from which 14 pedons were evaluated for infiltration. One minute and greater than 72 hour infiltration rates for the high, intermediate, and low elevations within the playas are given in Table 11.
While the variation of infiltration rates of the data set are quite large, it must be remembered what the data are portraying. This Vertisol is beset with abundant, deep cracks when it�s dry. The thesis from which the data were obtained (Evans, 1990), evaluated the bimodal cracking pattern of the Randall soil. The variability of the data were similar to that presented by Talsma and van der Lelij (1976) in an Australian vertisol. Infiltration variability is not only within playas, but also among playas. Unpublished data (Zartman, 1997) shows greater infiltration rates for the Randall soil in the Southern portions of this MLRA (Lubbock County) than in the Northern portion (Carson County). Figures 2 and 3 present Stage I and Stage III infiltration using double ring infiltrometers. Both Figs. 2 and 3 show greater infiltration rates in the southern playas as compared to the northern playas.
The Randall soil and its presence in MLRA 77 are being reevaluated. At one time all depressions in the Southern High Plains portion of MLRA 77 were classified as playas. The data presented in Figs. 1 and 2 above indicate that there are differences within the Randall series. As this document is written the Randall soil is being divided into 11 different soil series (Mr. T. Craig Byrd, NRCS, 1998). There are five depressional soils originally mapped as Randall, but lie outside of the current concept of playa lakes. Some of those soils that occupied the depressional areas of the landscape, while mapped as Randall, were not clay textured soils. Current soil survey reports have some sandy loam and clay loam soils mapped as the Randall. The Lamesa soil (fine-loamy, mixed, superactive, thermic Aeric Endoaqualfs) has aquic conditions at some times in most years, but has a sandy clay surface texture. The Lenorah fine sandy loam(fine-loamy, mixed, active calcareous thermic, Aeric Halaquepts) has a calcic horizon within 40 inches of the surface. The Cedarlake sandy clay loam (fine- loamy, mixed, superactive calcareous, thermic Typic Halaquepts) are found on the basins above the salt lakes of the region. The Segraves fine sandy loam fine-loamy, mixed, superactive, Typic Plaeustalfs) are playa-like depressions without the aquic conditions of a Randall. Lofton clay loam (fine, smectitic, thermic Vertic Argiustolls) is found on a slightly higher landscape position than the Randall.
Other soils are being separated from the Randall series due to the clay content or moisture conditions. One competing series is the Ranco (fine, smectitic, thermic, Ustic Epiaquerts). This soil is differentiated from the Randall by having 50% or less clay in the control section. Similar soils to be separated from the Randall are the Chapel (fine, smectitic, thermic Udic Calciusterts), Sparenberg (fine, smectitic thermic Udic Haplusterts), and McLean (fine, smectitic, thermic Udic Haplusterts). These three soils do not have aquic moisture conditions and have cracks that remain open for less than 150 cumulative days during most years. Other similar series are the Lazbuddie (fine, smectitic, thermic Typic Haplusterts) and Lockney (fine, smetitic, thermic Typic Haplusterts) that do not have aquic conditions and have cracks that remain open for 150 to 210 cumulative days during most years.
Summary The soils of MLRA 77 are some of the most extensively farmed soils in the world. The steppe features of this area were those that allowed for some of the first large scale mechanization, which are very common in agriculture today. This MLRA differs from many of the rest of the MLRAs of the southern region due to the vast expanse of arable lands. While the precipitation received is less than most southern MLRAs, the economies of scale make this region a very agriculturally productive one.
Literature Cited Bryant, R.B. 1977. A comparison of physical and chemical properties of selected irrigated, dryland and native range Texas High Plains soils. M.S. Thesis. Texas Tech Univ., Lubbock.
Buol, S.W. 1973. Soils of the Southern States and Puerto Rico. Southern Cooperative Series Bull. 174.
Evans, P.W. 1990. Determining the bimodal infiltration patterns in three playa lakes. M.S. Thesis. Texas Tech Univ., Lub-bock.
NRCS. 1996. Personal contact with Mr. W. Mike Risinger, Temple, Texas.
NRCS. 1998. Personal contact with Mr. T. Craig Byrd, Lubbock, Texas.
Layla, S.T. 1982. Influence of soil separates and mineralogy on soil-water content as affected by Super Slurper. M.S. Thesis. Texas Tech Univ., Lubbock.
Olson, C.G. (ed.) 1996. Bibliography of MLRA 77: A reference guide to publications of the Southern High Plains. p. 132. Ver 3.0. National Soil Survey Center, USDA-Natural Resources Conservation Service, Lincoln, Nebraska.
Paetzold, R.F. 1972. Water movement in selected Texas High Plains soils. M.S. Thesis. Texas Tech Univ., Lubbock.
Reddell, D.L. 1965. Water resources of playa lakes. Cross Section 12(3):1.
Seitlheko, E.M. 1975. Studies of mean particle size and mineralogy of sands along selected transects on the Llano Estacado. M.S. Thesis. Texas Tech Univ., Lubbock.
Talsma, T. and A.van der Lelij. 1976. Infiltration and water movement in an in situ swelling soil during prolonged ponding. Aust. J. Soil Res. 14:337-349.
Unger, P.W. 1975. Relationship between water retention, texture, density, and organic matter content of west and south central Texas soils. MP-11920. Texas Ag. Expt. Sta., College Station.
Unger, P.W. and F.B. Pringle. 1981. Pullman soils: Distribution, Importance, variability, and management. Texas Agric. Exp. Stn. Bull. No. 1372.
Unger, P.W. and F.B. Pringle. 1986. Sherm soils: Distribution, Importance, variability, and management. Texas Agric. Exp. Stn. Bull. No. 1513.
Unger, P.W. and F.B. Pringle. 1998. Olton soils: Distribution, Importance, variability, and management. Texas Agric. Exp. Stn. Bull. No. 1727.
Unger, P.W., F.B. Pringle, and D.A. Blackstock. 1993. Acuff soils: Distribution, Importance, variability, and management. Texas Agric. Exp. Stn. Bull. No. 1714.
USDA. 1981. Land resource regions and major land resource areas of the United States. Ag. Hndbk. #296. Washington, DC.
USDA. 1975. Soil Taxonomy. Ag. Handbook. #436. Washington, DC.
Zartman, R.E, P.W. Evans and R.H. Ramsey. 1994. Playa lakes on the Southern High Plains in Texas: Reevaluating infiltration. J. Soil Water Conserv. 49:299-301.
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