Environmental Engineering Reference
In-Depth Information
Wind
Movement of air above the turf canopy is an important factor influencing
evapotranspiration. In the absence of wind, the leaf surface is surrounded
by a thick
boundary layer
of air molecules that block free movement of
water molecules diffusing through leaf stomata and thus reduce water
loss. Wind disrupts this boundary layer, increasing evapotranspiration,
particularly under dry, warm conditions (Fig. 7.2).
Canopy resistance
Shoot density, leaf orientation, leaf area and growth rate all affect water
loss through turf canopy. These factors, described as
canopy resistance
,
may either increase or decrease evapotranspiration.
In modern turf management the use of evapotranspiration informa-
tion is gradually replacing older methods, such as examining soil mois-
ture conditions or visual symptoms of turf. The more advanced irrigation
systems use mini weather stations measuring rainfall, air temperature,
humidity and wind speed. This information is transmitted to a computer
programmed to estimate evapotranspiration for the turf-grass and main-
tenance regime in question. The computer, rather than a human, decides
when the irrigation system should be turned on and how long should it
run. Although computer programs are quite efficient and helpful and in
the future will probably be used to schedule irrigation systems on small
areas such as home lawns, they will never fully replace human know-
ledge combined with experience and ordinary common sense. A basic
Layer of humid air
Wind
Fig. 7.2. Wind disperses the thick boundary layer of humid air surrounding turf-grass
leaves.
