Soil Survey of Karnes County, Texas - Soil Data Mart - US ...

84 Soil Survey
climax plant species, and reduces infestations of
noxious weed and brush. However, desirable plants
can be severely damaged or killed if the soil surface is
too dry, allowing the fire to reach the plant crowns and
roots. Burning is not recommended more often than
once every three years to avoid interfering with the
regrowth cycle of perennial grasses. Prescribed
burning is an effective management tool that can be
substituted for chemical or mechanical treatment.
Planned Grazing Systems. The objective of this
practice is to rotate the grazing of livestock through
two or more pastures in a planned sequence for a
specified period of time. A planned grazing system
may be relatively simple in design when only two
pastures are used, or may be more complex and
management intensive when one or two herds and
many pastures are used. To be successful, it must be
tailored to conditions existing in each ranch unit and
meet the needs of the plants and animals as well as
the rancher.
Table 7 shows for each soil in the survey area that
supports range vegetation, the range site and the
potential annual production in favorable, average, and
unfavorable years. Only soils that are used as
rangeland or are suited to rangeland are listed.
A range site is listed for each soil map unit. The
relationship between soils and vegetation was
established during this survey; thus, range sites
generally can be determined directly from the soil
map. Soil properties that affect moisture supply and
plant nutrients have the greatest influence on the
productivity of range plants. Soil reaction, salt content,
and a seasonal high water table are also important.
Potential annual production is the amount of
vegetation that can be expected to grow annually on
well managed rangeland that is supporting the
potential natural plant community. It includes all
vegetation, whether or not it is palatable to grazing
animals. It includes the current year’s growth of leaves,
twigs, and fruits of woody plants. It does not include
the increase in stem diameter of trees and shrubs. It is
expressed in pounds per acre of air-dry vegetation for
favorable, average, and unfavorable years. In a
favorable year, the amount and distribution of
precipitation and the temperatures make growing
conditions substantially better than average. In an
unfavorable year, growing conditions are well below
average, generally because of low available soil
moisture.
Yields are adjusted to a common percentage of airdry
moisture content. The relationship of green weight
to air-dry weight varies according to such factors as
exposure, amount of shade, recent rains, and
unseasonable dry periods.
Following is a description of the 17 range sites in
Karnes County: Blackland, Chalky Ridge, Clay Loam,
Clayey Bottomland, Gravelly Ridge, Gray Sandy
Loam, Lakebed, Loamy Bottomland, Loamy Sand,
Rolling Blackland, Sandy, Sandy Loam, Shallow,
Shallow Ridge, Shallow Sandy Loam, Sloping Clay
Loam, and Tight Sandy Loam.
Blackland range site. The Elmendorf-Denhawken
complex soils, map unit EdB, are in the Blackland
range site. The climax vegetation is an open grassland
prairie. A few large live oaks, elm, and hackberry trees
are along drainageways and in motts. The composition
by weight is 95 percent grasses, and 5 percent forbs.
This site has high natural fertility. In climax stage,
little bluestem, indiangrass, and fourflower trichloris
produce almost half of the forage. Other grasses, such
as Arizona cottontop, sideoats grama, Texas
wintergrass, Texas cupgrass, tall dropseed, pinhole
bluestem, vine-mesquite, and plains bristlegrass,
produce the rest. Many palatable forbs and legumes
are native to the site.
Overgrazing by cattle eventually kills out the
decreaser grasses, such as fourflower trichloris,
indiangrass, sideoats grama, and little bluestem.
These are replaced by increaser plants, such as silver
bluestem, Texas wintergrass, tall dropseed, and other
mid grasses. If overgrazing continues, buffalograss,
Texas grama, tumblegrass, threeawns, annual weeds
and annual grasses invade the site along with noxious
brush species, such as mesquite, spiny hackberry,
Retama, agarito, lotebush, and huisache.
Chalky ridge range site. The Shiner soil, map unit
SrD, is in the Chalky Ridge range site. This site is a
true prairie site. Large liveoak trees, occuring either
singly or in small motts, offer some shade. The
scattered trees, rolling topography and many native
flowering forbs make this an attractive site. The
composition by weight is 85 percent grasses, 10
percent forbs, and 5 percent woody plants.
The herbaceous plant community is dominated by
little bluestem, which generally makes up a little more
than half of the total grass composition. Indiangrass,
big bluestem, Florida paspalum, and Canada and
Virginia wildrye are also important and are often the
dominant grasses. Sideoats grama, silver bluestem,
and tall dropseed are mid grasses usually present in
smaller amounts. Many forbs and legumes provide
valuable grazing and an attractive landscape.
As retrogression occurs, the tall grass species
decrease and are replaced by sideoats grama, Texas
wintergrass, silver bluestem, buffalograss, threeawns,
and less palatable forbs. With continued abuse, short
grasses, such as red grama, hairy grama, Texas
grama, tumblegrass, and threeawns, invade along with