MLRA 87: Texas Claypan Area
C.L. Munster and R.L. Rhykerd
Texas A&M University
This major land resource area (MLRA 87) occupies 2,405,346 ha (5,939,126
acres) in east central Texas. It occurs east of MLRA 86. Much of this information
was obtained from county soil survey reports of this region.
Annual precipitation in MLRA 87 is approximately 1000 mm with about
half falling between April and September, which includes the growing season
for most crops. Thunderstorms occur approximately 47 days per year, primarily
in the spring. The average seasonal snowfall is about 30 mm. The average
relative humidity is about 60% during midday and 80% at dawn. During the
summer months, the sun shines 65% of the time possible and 50% of the time
during the winter months. Winds prevail from the south to southeast. Highest
average wind speeds occur during the spring at approximately 21 km/h. In
the winter months the average daily high temperatures is 9°C with a
low temperature of 2°C. In the summer, the average daily temperature
is about 28°C with an average daily maximum temperature of 34°C.
Average annual temperature is approximately 18°C. The average number
of frost-free days is 258 and the average number of growing degree-days
is approximately 6200.
Geology and Topography
MLRA 87 is located in east central Texas and composes the area known
as the Texas Claypan Area. This area is mostly gently sloping with some
parts nearly level and some moderately steep to steep. Elevation ranges
from 40 to 210 m. The dominant light-colored loamy and sandy soils of the
Texas Claypan Area formed under native savannah vegetation of oak trees
and mid and tall grasses.
The landuse of MLRA 87 is mostly forests and mixed landuses with forests
and cropland and/or range accounting for over 90% of the land area.
Livestock, hay, and crops are the main agricultural enterprises in this
region. Crop production, mainly cotton and corn, were once the primary
landuse. However a significant conversion of land from cultivation of crops
to production of forage grasses has greatly increased the importance of
livestock in the area. This conversion has occurred primarily on the less
productive cultivated soils in the region. The production of beef cattle
primarily from cow-calf operations is the most important source of agricultural
income. Livestock are pastured year-round but require hay and feed supplements
in the winter. Improved cool-season grasses and legumes may be provided
for grazing in the winter and spring. Some small grain crops are grown
in this region, although water erosion is a major concern because it reduces
the productivity of the land.
Soil is the most important resource in this MLRA. Livestock, hay, and
forage crops are the main source of income. Lignite mining, oil, and gas
are also important sources of income for this area. In addition, water
is also an important resource in this area with many lakes and rivers providing
fresh water to this region.
Water is relatively abundant throughout the region. Precipitation is
adequate for crops in most years. In 2 out of 10 years, rainfall from April
to September is less than 200 mm leading to reduced yields, and in other
years excess rainfall can delay planting or interfere with harvesting.
About 47 thunderstorms occur per year, mostly during the summer. Additional
water is available from underground sources, lakes, and rivers.
Most of the soils in this area belong to the Texas Claypan Area Major
Land Resource area. The dominant soil series in this area are the Padina,
Crockett, Silstid, Gredge, Tabor, Edge, Straber, Axtell, and Tremona, which
represent about 40% of the soils in this region (Table
1). STATSGO soils are presented in Fig. 1.
The Padina series consists of deep, gently sloping to moderately steep,
moderately well drained soils on uplands. These soils are moderately slowly
permeable. They form in thick beds of sandy material. The Crockett series
consists of deep, gently sloping to strongly sloping, moderately well drained
soils on uplands. These soils are very slowly permeable. They formed in
alkaline shale and clay. The Silstid series consists of deep, gently sloping,
and well drained soils on uplands. They formed in beds of sandy or loamy
material and interbedded sandstones. The Gredge series consists of very
deep, well drained, very slowly permeable soils on erosional Pleistocene
terraces. The soil formed in loamy and clayey sediments. The Tabor series
consists of deep, gently sloping, moderately well drained soils on uplands.
These soils are very slowly permeable. They formed in acid to alkaline
interbedded clayey and loamy material. The Edge series consists of a very
deep well-drained very slowly permeable soil on uplands. These soils formed
in mostly loamy and sandy materials derived mainly from the Calvert Bluff
and Hooper members of the Wilcox Formation. The Straber series consists
of very deep, moderately well drained, very slowly permeable soils that
formed in alkaline clayey and loamy materials. The Axtell series consists
of deep, nearly level to strongly sloping, moderately well drained soils
on old terraces. These soils are very slowly permeable. The Tremona series
consists of very deep, somewhat poorly drained, very slowly permeable soils
that formed in interbedded sandy, clayey, and loamy materials. They formed
in acid to alkaline clayey sediments. Various physical properties of these
soils are presented in Table 2. Many of
these clay soils show a significant temporal change in hydraulic conductivity
depending on the water content of the soil, and may have a very high initial
infiltration rate depending the moisture status of the soil. Infiltration
rates after prolonged dry spells may be 100 to 200 micrometers per second
(Lin et al., 1998; Lin et al 1997).
Lin, H.S., K.J. McInnes, L.P. Wilding, and C.T. Hallmark. 1998. Macroporosity/moisture
effect on infiltration rates in vertisols and vertic intergrades. Soil
Lin, H.S., K.J. McInnes, L.P. Wilding, and C.T. Hallmark. 1997. Low
tension water flow in structured soils. Can. J. Soil Sci. 47:649-654.
USDA, 1998. NRCS, National Cartography & Geospatial Center. Fort