This major land resource area (MLRA 78)
occupies about 13 million ha (32.11 million acres) in southern Kansas (0.3%
of the total MLRA), western Oklahoma (32.7%), and the panhandle of Texas
(67%). Much of the general information in this section was excerpted from
About 60% of MLRA 78 is rangeland, and
35% is cropland. The rest of the area is urban land, woodland, or pasture.
Nearly all the area is in farms or ranches. Most rangeland is in the west,
but some is throughout the area. Ranges and pastures are grazed mainly
by beef cattle. Winter wheat and grain sorghum are the major cash crops
grown throughout the area. Cotton (Gossypium
hirsutum L.) is an important
crop south of the Cimarron River; alfalfa and peanuts are important locally.
The crops grown under irrigation are also grown in nonirrigated areas.
Soil erosion is a major concern of management if the soils are cultivated
or if range and pasture are overgrazed.
Elevation in MLRA 78 ranges from 500
to 900 m, increasing gradually from east to west. On these dissected plains,
the broad divides are nearly level to gently sloping, but slopes are short
and steep in the valleys. In places the valleys are bordered by a rolling
to steep irregular dune topography. Local relief is mainly in meters, but
a few of the larger valleys are tens of meters or more below the general
level of the plain. In southwestern Oklahoma, the Wichita Mountains are
as much as 300 m above the surrounding plains.
Average annual precipitation in MLRA
78 ranges from 500 to 750 mm, increasing from west to east (Fig. 1). Maximum
precipitation is in spring, and the minimum is in winter. Snowfall ranges
from 25 cm in the north to 10 cm in the south. The average annual temperature
is from 4 to 18 oC,
with an average of 185 to 230 freeze-free days. A typical distribution
of annual precipitation for the MLRA is shown in Fig. 2.
Fig. 1. Spatial distribution of long-term average annual precipitation
in southern region of United States. This precipitation map is based on
data from W. H. William at Oak Ridge National Laboratory
Fig. 2. Typical temporal distribution of annual precipitation for
MLRA 78. The long-term monthly precipitation data for the graph was obtained
from a weather station at Erick, Oklahoma, which is located near the center
of the MLRA.
This area supports mid and tall grasses.
Sand bluestem, little bluestem, and sand sagebrush are dominant on the
coarse textured soils. Little bluestem, gramas, and associated grasses
and forbs grow on the finer textured soils.
The moderate but somewhat erratic precipitation
supplies water for range and crops. Small ponds on individual farms provide
water for livestock. Some larger ponds on individual farms are used for
flood control, recreation, irrigation water, or water for livestock. A
few large ponds and reservoirs are a source of municipal water and irrigation
water. Rivers are a potential source of water for irrigation. Water in
some of the larger rivers is highly mineralized. The deep sand and gravel
in valleys yield some ground water. In sloping areas where the underlying
sandstone and shale are near the surface, ground water is scarce.
The major soils are Ustolls, Ustalfs,
and Ochrepts. They have a thermic temperature regime, an ustic moisture
regime, and mixed mineralogy. The nearly level to gently sloping, well
drained and moderately well drained, deep Argiustolls (Abilene, Carey,
and St. Paul series), Paleustolls (Hollister, Rotan, Sagerton, and Tillman
series), and Natrustolls (Foard series) are on uplands. The Ustalfs mainly
are deep and sandy or loamy and have a loamy subsoil. They have a thermic
temperature regime and mixed mineralogy. The nearly level to undulating
or rolling, well drained, deep Haplustalfs (Devol and Grandfield series)
and Paleustalfs (Miles, Springer, Wichita, Winters, and Nobscot series)
are on uplands. The gently sloping to moderately steep Ustochrepts (Dill,
Enterprise, Hardeman, Obaro, Quinlan, Vernon, and Woodward series) are
on uplands. Ustifluvents (Clairemont, Lincoln, Mangum, Yomont, and Yahola
series) are minor soils on flood plains. The major soil series in MLRA
78 and selected physical properties of the major soils are listed in Tables
1 and 2. STATSGO soils are depicted in Fig. 3.
Fig. 3. STATSGO soils of the Central Rolling Red Plains MLRA 78.
and Chemical Transport
Limited data on hydraulic properties
for selected soils in MLRA 78 exist and well-documented data on chemical
transport in the soils of this MLRA is scarce. Ouattara (1977) used a horizontal
calibrated capillary tube to measure saturated hydraulic conductivity of
Tillman-Hollister clay loam. An average vertical hydraulic conductivity
of 0.15 cm day-1 was obtained with a standard deviation of 0.211
cm day-1 for the 130-cm deep soil profiles. The ratio
of the hydraulic conductivity values from samples at different depths of
the soil profile can be as large as 7 (Fig. 4).
Fig. 4. Saturated hydraulic conductivity of Tillman-Hollister clay
loam at different depths.
Davidson (1977, unpublished), Nofziger
et al. (1983), and Williams (1980) used modified Buchner funnels to determine
soil water retention curves at relatively low suctions (up to 152 cm of
water) and pressure plate extractors to determine water contents at higher
suctions. They employed instantaneous profile method (Hillel et al., 1972)
to measure unsaturated hydraulic conductivity in the field. Tensiometers
were installed at 0.15, 0.3, 0.45, 0.6, 0.75, 0.9, 1.2, and 1.5 m depths
to determine average hydraulic gradients across soil layers in the hydraulic
conductivity measurement while water contents were measured by neutron
scattering. Soil cores for retention curve measurements were taken at each
tensiometer depth from the edge of the plots with tensiometer installations.
Like the saturated hydraulic conductivity in Fig. 4, the retention curves
and unsaturated hydraulic conductivity of different layers in a soil profile
exhibited significant variations (Figs. 5 and 6).
Fig. 5. Water retention curves of soil samples of different textural
classes from three soil profiles of Tipton sandy loam. The three sites
are located within a 2-km region.
Fig. 6. Unsaturated hydraulic conductivity for layers of different
texture classes from three soil pro-files of Tipton sandy loam. The three
sites are located within a 2-km region.
Figures 5 and 6 also exhibit apparent
grouping of retention curves and hydraulic conductivity by texture classes
(i.e. data points of retention curves of soil samples from different depths
and unsaturated hydraulic conductivity of different layers in a soil profile
are clustered into separate groups by texture classes). Therefore, retention
curves of soil samples of the same texture class from different depths
in a soil profile are lumped together for an average retention curve of
that texture class. Similar things are done for hydraulic conductivity
from different layers of the same texture class in a soil profile.
Tables 3 to 4 summarize the typical texture stratification and the
hydraulic properties of selected soils in MLRA 78. The data for Cobb loamy
sand, Cobb sandy loam, McLain silty clay loam, Port silty clay, Teller
loam and Zaneis loam were provided by Davidson (unpublished) while the
data on Tipton sandy loam were obtained in a southern region project (Nofziger
et al., 1983). The h in
4 is soil water potential, q
soil water content, and K
unsaturated hydraulic conductivity. The value in the parentheses after
a water content in Table 4 is the standard deviation associated with the
water content corresponding to the soil water potential on the left. For
a texture class occurring at more than one sampled depth, the standard
deviation includes both cross-replicate and cross-depth variation. The
measured hydraulic conductivity associated with a specific soil water potential
in a soil texture class may vary by 1 order of magnitude in range. Itís
worthwhile to notice that the measured hydraulic conductivity for layers
of sandy loam texture in Fig. 6 form two separate groups while retention
curves of the samples of the same texture class fall into one group in
Fig. 5. The hydraulic conductivity of the sandy loam layer between 0- and
15-cm depths is lower than that between 30- and 90-cm depths by almost
one order of magnitude. A plausible reason for this discrepancy may lie
in the difference in bulk density in these two layers (Fig. 7).
Fig. 7. Bulk density of Tipton sandy loam at different depths.
Davidson, J.M. (unpublished). Measured
hydraulic properties of Cobb loamy sand, Cobb sandy loam, McLain silty
clay loam, Port silty clay, Teller loam, and Zaneis loam. University of
Hillel, D., V.D. Krentos, and Y. Stylianou.
1972. Procedure and test of an internal drainage method for measuring soil
hydraulic characteristics in
situ. Soil Sci. 114:395-400.
Nofziger, D.L., J.R. Williams, A.G. Hornsby,
and A.L. Wood. 1983. Physical characteristics of soils of the southern
region - Bethany, Konawa, and Tipton series. Southern Cooperative Series
Bull. 265, Project No. S-124. Agricultural Experiment Station, Oklahoma
State University, Stillwater.
Ouattara, M. 1977. Variation of saturated
hydraulic conductivity with depth for selected profiles of Tillman-Hollister
soil. Master degree thesis, Oklahoma State University, Stillwater.
USDA. 1981. Land Resource Regions and
Major Land Resource Areas of the United States. United States Department
of Agriculture, Soil Conservation Service Handbook 296.
USDA. 1994. State Soil Geographic (STATSGO)
Data Base data use information. National Cartography and GIS Center, United
States Department of Agriculture, National Resources Conservation Service,
Fort Worth, Texas.
Williams, J.R. 1980. Spatial variability
of unsaturated hydraulic conductivity of Tipton soil series. M.S. thesis,
Oklahoma State University, Stillwater.