Soil Survey of Limestone County, Texas Page: 3

                                
Limestone County, Texas

of the southern and eastern parts of the county have ample
supplies of good quality underground water.
Fish and wildlife are other important natural resources in
Limestone County. Most of the southern part of the county
is leased for deer hunting, which provides added income to
landowners.
Climate
Limestone County is hot in summer and cool in winter
when an occasional surge of cold air causes a sharp drop
in otherwise mild temperatures. Rainfall is uniformly
distributed throughout the year, reaching a slight peak in
spring. Snowfalls are infrequent. Annual total precipitation
is normally adequate for grain sorghum, corn, cotton, and
wheat.
Table 1 gives data on temperature and precipitation for
the survey area as recorded at Mexia, Texas in the period
1961 to 1990. Table 2 shows probable dates of the first
freeze in fall and the last freeze in spring. Table 3 provides
data on length of the growing season.
In winter, the average temperature is 48 degrees F and
the average daily minimum temperature is 36 degrees.
The lowest temperature on record, which occurred on
December 23, 1989, is -5 degrees. In summer, the
average temperature is 82 degrees and the average daily
maximum temperature is 94 degrees. The highest recorded
temperature, which occurred on July 26, 1954, is 110
degrees.
Growing degree days are shown in table 1. They are
equivalent to "heat units." During the month, growing
degree days accumulate by the amount that the average
temperature each day exceeds a base temperature (50
degrees F). The normal monthly accumulation is used to
schedule single or successive plantings of a crop between
the last freeze in spring and the first freeze in fall.
The total annual precipitation is about 40 inches. Of this,
21 inches, or about 51 percent, usually falls in April through
September. The growing season for most crops falls within
this period. In 2 years out of 10, the rainfall in April through
September is less than 8 inches. The heaviest 1-day
rainfall during the period of record was 8.7 inches on
February 4, 1986. Thunderstorms occur on about 45 days
each year, and most occur in spring.
The average seasonal snowfall is about 1.3 inches. The
greatest snow depth at any one time during the period of
record was 5 inches. The number of days with at least 1
inch of snow on the ground varies greatly from year to year.
The average relative humidity in midafternoon is about
60 percent. Humidity is higher at night, and the average at
dawn is about 80 percent. The sun shines 65 percent of the
time possible in summer and 50 percent in winter. The
prevailing wind is from the south. Average windspeed is
highest, 13 miles per hour, in spring.

Tornadoes and severe thunderstorms occur
occasionally. These storms are local and of short duration,
and the pattern of damage is variable and spotty.
How This Survey Was Made
This survey was made to provide information about the
soils and miscellaneous areas in the survey area. The
information includes a description of the soils and
miscellaneous areas and their location, and a discussion of
their suitability, limitations, and management for specified
uses. Soil scientists observed the steepness, length, and
shape of the slopes; the general pattern of drainage; the
kinds of crops and native plants; and the kinds of bedrock.
They dug many holes to study the soil profile, which is the
sequence of natural layers, or horizons, in a soil. The
profile extends from the surface down into the
unconsolidated material in which the soil formed. The
unconsolidated material is devoid of roots and other living
organisms and has not been changed by other biological
activity.
The soils and miscellaneous areas in the survey area
are in an orderly pattern that is related to the geology,
landforms, relief, climate, and natural vegetation of the
area. Each kind of soil and miscellaneous area is
associated with a particular kind of landform or with a
segment of the landform. By observing the soils and
miscellaneous areas in the survey area and relating their
position to specific segments of the landform, a soil
scientist develops a concept or model of how they were
formed. Thus, during mapping, this model enables the soil
scientist to predict with a considerable degree of accuracy
the kind of soil or miscellaneous area at a specific location
on the landscape.
Commonly, individual soils on the landscape merge into
one another as their characteristics gradually change. To
construct an accurate soil map, however, soil scientists
must determine the boundaries between the soils. They can
observe only a limited number of soil profiles.
Nevertheless, these observations, supplemented by an
understanding of the soil-vegetation-landscape relationship,
are sufficient to verify predictions of the kinds of soil in an
area and to determine the boundaries.
Soil scientists recorded the characteristics of the soil
profiles that they studied. They noted color, texture, size
and shape of soil aggregates, kind and amount of rock
fragments, distribution of plant roots, reaction, and other
features that enable them to identify soils. After describing
the soils in the survey area and determining their
properties, the soil scientists assigned the soils to
taxonomic classes (units). Taxonomic classes are
concepts. Each taxonomic class has a set of soil
characteristics with precisely defined limits. The classes
are used as a basis for comparison to classify soils