|
A
pasture plant faces adversity created by numerous factors, one of the
most important of which is other plants growing in association with it.
Pests, climatic conditions, and soil factors can create challenges, but
survival is made even more difficult when neigh-boring plants are
competing for the same resources needed for survival and growth.
Nutrients-
Pasture plants do best when adequate nutrients are available, and a
given plant may have difficulty getting its share of soil nutrients due
to uptake by nearby plants, especially if neighboring plants have a more
extensive or more favorably placed root system. The timing of fertilizer
applications may also favor certain pasture species over others. For
example, applications of nitrogen fertilizer only in early spring and
early autumn favor cool season grasses, while applications only during
summer favor warm season grasses.
Furthermore,
the type of fertilizer applied may favor certain pasture species over
others. Fertilizing a grass/legume mixture with nitrogen tends to favor
the grass, because this practice stimulates competition against the
legume. The reverse may be true if only phosphate and potash fertilizer
is applied. Proper fertilization, especially with potash, also has an
extremely important influence on the susceptibility of many forage
species to winterkill.
Soil
Moisture-
Competition for soil moisture is obviously often a key reason for
persistence of some plant species and not others in a certain area. This
may be associated with some species having deeper and more extensive
root systems, a protective mechanism for reducing water loss during
drought periods, or other factors. Competition for moisture (without
providing good quantity and/or quality of forage) is one of the primary
reasons why weeds are undesirable in pastures. Conversely, some plants
are more tolerant of high levels of soil moisture than others and thus
more competitive in moist areas.
Light-
Plants cannot compete well or even survive without adequate light, but
there is great variation in the amount of shade tolerance of various
plant species. The greater the extent to which a forage plant is shaded
by plants growing in association with it, the more difficult it will be
for that forage plant to survive. One of the benefits of proper grazing
management is that it helps ensure that desirable plants are receiving
enough light.
Allelopathy-
This term refers to the secretion of chemical com-pounds by a plant that
has an adverse effect on the establishment and/or growth of other
plants. The inhibitory effects can be against plants of a different
species or even of the same species. An example of same-species
allelopathy is that established alfalfa plants can inhibit germination
of alfalfa seed and growth of seedling alfalfa plants. Allelopathy is
probably more common and important than is presently generally realized. |
