|
General
climatic conditions vary throughout the South. Knowledge of these
conditions, together with knowledge of the requirements of various
forage varieties or species, allows us to make general statements about
their geographic adaptation. Yet, there can be specific location
influences that mitigate or intensify general climatic influences and
create "microclimates" within a farm or field.
Some
location-related climate factors can be influenced by a livestock
producer’s management while others cannot. However, a producer needs
to at least be aware of the existence of various location influences
because they may explain or help explain the dominance or demise of
particular plants in particular areas.
Soil
Type– Two
important reasons why soil type is important are that it affects the
moisture-holding capacity and the nutrient-holding capacity of the soil.
In addition, infiltration of water, crusting, and the extent of
"heaving" of plants during freezing and thawing are different
in various soils. Finally, some soils naturally contain and release
higher levels of certain nutrients than others.
Soil
pH and Fertility–
The acidity or alkalinity of a soil is measured on a 14 point scale with
7.0 being neutral and numbers above or below this level being basic or
acid, respectively. This is a logarithmic scale. Thus, a pH of 5.0 is
ten times more acid than one of 6.0. Most soils within the South tend to
be acid, but a few are near neutral or alkaline. Soil pH has an
important influence on the survival and competitiveness of plants. In
general, grasses are more tolerant of soil acidity than are legumes.
Some forage crops are tolerant of a wide range of soil pH, while others
are much more limited. For example, bermudagrass can tolerate highly
acid or quite alkaline conditions, while alfalfa requires a pH of 6.5 to
around 8.0. Some weeds are also quite sensitive to soil pH.
Fertility
also has a major impact on plant growth and survival, and some plants
require much a much higher fertility level than others. Fortunately,
inherent fertility limitations that some soils have can be overcome
through soil testing and the application of needed nutrients.
Drainage–
Both the internal and external drainage of a field affect plant growth
and survival. Alfalfa, orchardgrass, and arrowleaf clover are examples
of forage crops that require good drainage, while reed canarygrass,
white clover, and tall fescue are much more tolerant of moist soil.
Obviously,
there is more runoff and less opportunity for water infiltration on a
hillside than on a relatively flat area. This accounts for the
often-observed situation in the mid- and upper South in which hillsides
in a pasture may contain substantial amounts of sericea lespedeza and
common bermudagrass, both of which require good drainage, while bottoms
or areas between hills may consist primarily of tall fescue, white
clover, and/or dallisgrass, which require better moisture availability.
Various rushes and sedges are undesirable plants that are frequently
found in wet areas such as along the edges of waterways or in low-lying
portions of fields.
Elevation–
The highest point in a field can be the area in which plants are
severely stressed by wind. High areas also tend to be the most eroded
parts of fields, and therefore the soil may be less productive. However,
the lowest point in the field is likely to be the coldest area where
winterkill is most likely.
Exposure–
The direction a slope faces can have an important influence on plant
competition, especially for plants that are only marginally adapted in
an area. Southern slopes receive more sunlight and are warmer than
northern slopes, thus reducing the likelihood of winterkill. The
opposite situation can occur with cool season plants that are sensitive
to heat stress. For example, timothy and Kentucky bluegrass are only
marginally adapted in the mid-South. Therefore, other things being
equal, they would be more likely to persist on northern, or to a lesser
extent, eastern slopes.
Color
of Soil and Ground Cover–
A higher percentage of the sunlight reaching a field is absorbed if the
field is dark, rather than light, in color. Therefore, factors such as
soil type and pasture height can also affect the extent of reflectance
of sunlight.
Shading–
The height to which a pasture is grazed has an extremely important
influence on shading of individual leaves within a pasture sward. In
addition, trees, buildings and other |
