Soil Survey of Jackson County, Texas Page: 58
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Soil Survey
inches in diameter based on an ovendry weight. The
sieves, numbers 4, 10, 40, and 200 (USA Standard
Series), have openings of 4.76, 2.00, 0.420, and 0.074
millimeters, respectively. Estimates are based on
laboratory tests of soils sampled in the survey area and
in nearby areas and on estimates made in the field.
Liquid limit and plasticity index (Atterberg limits)
indicate the plasticity characteristics of a soil. The
estimates are based on test data from the survey area
or from nearby areas and on field examination.
Physical and Chemical Properties
Table 14 shows estimates of some characteristics
and features that affect soil behavior. These estimates
are given for the major layers of each soil in the survey
area. The estimates are based on field observations
and on test data for these and similar soils.
Clay as a soil separate, or component, consists of
mineral soil particles that are less than 0.002 millimeter
in diameter. In this table, the estimated clay content of
each major soil layer is given as a percentage, by
weight, of the soil material that is less than 2 millimeters
in diameter.
The amount and kind of clay greatly affect the fertility
and physical condition of the soil. They determine the
ability of the soil to adsorb cations and to retain
moisture. They influence the shrink-swell potential,
permeability, plasticity, the ease of soil dispersion, and
other soil properties. The amount and kind of clay in a
soil also affect tillage and earthmoving operations.
Moist bulk density is the weight of soil (ovendry) per
unit volume. Volume is measured when the soil is at
field moisture capacity, that is, the moisture content at
1/3-bar moisture tension. Weight is determined after
drying the soil at 105 degrees C. In this table, the
estimated moist bulk density of each major soil horizon
is expressed in grams per cubic centimeter of soil
material that is less than 2 millimeters in diameter. Bulk
density data are used to compute shrink-swell potential,
available water capacity, total pore space, and other
soil properties. The moist bulk density of a soil indicates
the pore space available for water and roots. A bulk
density of more than 1.6 can restrict water storage and
root penetration. Moist bulk density is influenced by
texture, kind of clay, content of organic matter, and soil
structure.
Permeability refers to the ability of a soil to transmit
water or air. The estimates indicate the rate of
movement of water through the soil when the soil is
saturated. They are based on soil characteristics
observed in the field, particularly structure, porosity, and
texture. Permeability is considered in the design of soil
drainage systems and septic tank absorption fields.Available water capacity refers to the quantity of
water that the soil is capable of storing for use by
plants. The capacity for water storage in each major soil
layer is stated in inches of water per inch of soil. The
capacity varies, depending on soil properties that affect
the retention of water and the depth of the root zone.
The most important properties are the content of
organic matter, soil texture, bulk density, and soil
structure. Available water capacity is an important factor
in the choice of plants or crops to be grown and in the
design and management of irrigation systems. Available
water capacity is not an estimate of the quantity of
water actually available to plants at any given time.
Soil reaction is a measure of acidity or alkalinity and
is expressed as a range in pH values. The range in pH
of each major horizon is based on many field tests. For
many soils, values have been verified by laboratory
analyses. Soil reaction is important in selecting crops
and other plants, in evaluating soil amendments for
fertility and stabilization, and in determining the risk of
corrosion.
Salinity is a measure of soluble salts in the soil at
saturation. It is expressed as the electrical conductivity
of the saturation extract, in millimhos per centimeter at
25 degrees C. Estimates are based on field and
laboratory measurements at representative sites of
nonirrigated soils. The salinity of irrigated soils is
affected by the quality of the irrigation water and by the
frequency of water application. Hence, the salinity of
soils in individual fields can differ greatly from the value
given in the table. Salinity affects the suitability of a soil
for crop production, the stability of soil if used as
construction material, and the potential of the soil to
corrode metal and concrete.
Shrink-swell potential is the potential for volume
change in a soil with a loss or gain in moisture. Volume
change occurs mainly because of the interaction of clay
minerals with water and varies with the amount and
type of clay minerals in the soil. The size of the load on
the soil and the magnitude of the change in soil
moisture content influence the amount of swelling of
soils in place. Laboratory measurements of swelling of
undisturbed clods were made for many soils. For
others, swelling was estimated on the basis of the kind
and amount of clay minerals in the soil and on
measurements of similar soils.
If the shrink-swell potential is rated moderate to very
high, shrinking and swelling can cause damage to
buildings, roads, and other structures. Special design is
often needed.
Shrink-swell potential classes are based on the
change in length of an unconfined clod as moisture
content is increased from air-dry to field capacity. The
classes are low, a change of less than 3 percent;58
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Miller, Wesley L. Soil Survey of Jackson County, Texas, book, May 1997; Washington D.C.. (https://texashistory.unt.edu/ark:/67531/metapth224539/m1/68/: accessed April 26, 2024), University of North Texas Libraries, The Portal to Texas History, https://texashistory.unt.edu; crediting UNT Libraries Government Documents Department.