Irrigating Lawns
There is only
one proven method for watering lawn areas, through
the use of popup
spray heads. Although subsurface
trickle irrigation has
been developed for use in lawns, installation is
costly and renovation of the lawn soil is required
in order for it to be effective.
Lawn grasses require
considerably less water to remain green and healthy
than most people may think, but even distribution
of the applied water is essential. It is important
to remember that a lawn is not a single plant, but
rather a collection of thousands (or tens of thousands)
of tiny individual plants, each with its own very
localized root system. Because of this, every square
inch of the lawn must be covered by the sprays. Attempting
to compensate for gaps in coverage by watering longer
will not work as lateral (capillary) movement of
absorbed water through the soil is extremely limited
and the un-watered areas will never draw enough moisture
to thrive. Instead, this will only result in wasting
water by flooding the areas of heavier spray. Overwatering
of lawns will lead to fungal diseases and de-oxygenating
compaction of the soil.
The most important
factors in maintaining water use efficiency with
regard to lawns are as follows:
System
Design - Coverage must be balanced over
the whole lawn. Because most sprayheads by design
do not deliver much water close to the head itself,
the location of each head must be receiving spray
from another adjacent head. This is referred to
as 'head-to-head coverage'. Two principle types
of sprayheads are used for lawn watering: fixed-arc
sprays and gear
rotors. Fixed-arc (fan)
sprays are more versatile and provide more even
coverage than rotors, but considerably more heads
are required. Rotors spray greater distances by
shooting a narrow stream of water while rotating,
making them more cost-effective for watering large,
geometric lawns and playing fields, but useless
for lawn areas with single dimensions of less than
20'. Because the two have different scheduling
requirements. fixed-arc sprays and rotors should
never be combined on a single irrigation zone.
Sprayhead
Adjustment - Almost all sprayheads are
adjustable and should be checked before being put
into use in the spring to avoid spraying walkways,
roadways, walls and other structures. This is a
simple procedure which will greatly reduce water
waste.
Scheduling -
Watering of lawns too often or for too long each
session is the single largest contributor to irrigation
water waste. The amount of water actually needed
to keep grass a healthy green is specific to the
site, with soil type, slope, sun exposure and proximity
of large trees all being factors. All lawn areas
on a single property should therefore not simply
be scheduled for the same amount of watering, but
should be adjusted individually. Zones of rotors,
because they are distributing the same amount of
water as fixed-arc sprays but over a greater area,
may need to run up to 50% longer. Most importantly,
watering should always be scheduled for the early
morning hours when mains pressure is highest and
water is not being immediately lost to evaporation.
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