Environmental Engineering Reference
In-Depth Information
forced to grow beyond its normal rate, as it does after application of
fertilizer or after the loss of leaves to mowing. Plants must maintain
reserves for the future. The level of storage reserves is a good indicator
of how well a plant will survive stressful conditions, such as drought,
disease infection, insect damage or excessive traffic.
The four principal physiological processes are therefore interrelated.
Under high photosynthesis enough energy is captured and enough car-
bohydrates produced to support growth, storage and respiration. If
photosynthesis decreases, stored products must be used for respiration
and growth. For example, mowing turf too low (scalping) removes too
much leaf area and disturbs photosynthesis, causing the turf plant to
'borrow' energy from storage to maintain respiration and to be able to
regrow. Repeated scalping may deplete storage and may lead to starva-
tion and possibly death of the plant. Any cultural practice that increases
growth, such as fertilization, uses up carbohydrates that would otherwise
be sent to storage. Whenever a plant is fertilized, growth is stimulated
and storage is reduced. Frequent fertilization may therefore harm plants
with low storage reserves, and when those plants undergo stress, they
may suffer great damage. Understanding how plants grow and respond
to the environment is essential to maintenance of high-quality turf. Good
turf management requires knowledge of basic physiological processes
that take place in plants and use of that knowledge to best advantage.
Morphology
Shoots
As indicated in Fig. 1.7, the above-ground part of the plant is known as
the
shoot
. A grass shoot consists of
leaves
,
stem
and
inflorescence
. Each leaf
is composed of two defined parts: (i) the upper, mostly flat part, called
the
blade
; and (ii) the lower, often tubular part, called the
sheath
. The
swollen areas along the stem where leaves are attached are called
nodes
.
The node is the point at which the vascular system of the leaf is attached
to that of the stem. At each node, in the angle between the leaf and the
stem, is a
bud
, from which new stem growth can originate. An abundance
of buds assures continuous formation of new stems and uninterrupted
growth of the grass plant. The portions of the stem between nodes are
called
internodes
. Internode length in most turf-grasses ranges from a
fraction of a millimetre to several centimetres. Turf density depends
highly on internode length. Shorter internodes result in higher density
of a turf's canopy.
Very close to ground level, numerous nodes with very short inter-
nodes are stacked on top of each other, forming the
crown
(Fig. 1.8). The
