Irrigation
... Micro-Sprinklers
(Adapted
from the November 1996 Olives
Australia Newsletter)
Will
I water by hand or flood irrigate? Or will I use sprinklers
or drippers or some other watering method advocated by my knowledgeable
neighbour? What is best for my olives?
Well,
we don't pretend to know what is "best", but from
a lot of observations and discussions with growers and
irrigation equipment manufacturers we believe we've climbed
a reasonable distance up the basic ladder when it comes to irrigating
olive trees.
Let's
share a few thoughts on watering olive trees as we lead
up to discussing a product we've become reasonably impressed
with.
If
you choose to water your trees by hand then as
the root system grows larger and needs more water, you'll
have to spend more and more time on that job resulting in less
and less time for the other important things of life. And if
you get sick, who's going to water them as well as you do?
What
about flood irrigation? Many growers have changed
from flood irrigation to under-tree sprinklers because of unevenness
of water application with some trees receiving too much
water, especially in the lower ends of the flood irrigated
orchard. Maintenance of banks, water wastage and unevenness
of fertiliser application to each tree are also considered
to be problems worth considering.
Under-tree
drippers are very inexpensive and water the tree's
root zone reasonably well for up to twelve months or so.
The dripper produces a football shaped water pattern beneath
the soil and the roots tend to concentrate in that area
with little encouragement to move out further. As the
tree grows, many more drippers will finally need to be added
to give a reasonably even water supply to the roots. One dripper
is cheap, but many drippers can become quite expensive. Some
growers place a dripper on either side of a mature tree and
think they've adequately irrigated it - not so! In nature,
the olive tree has a wide and strong root system that can handle
a man-made tree shaker. One or two drippers won't encourage
the development of the extensive root system needed and
root limitations can result.
Then
what happens if you miss a watering, or worse still, run
out of water? Here is what manufacturers of the drip irrigation
equipment tells us happens. The tree needs the water and the
water in the concentrated root zone at the dripper position
is quickly sucked up to feed the tree. If another application
of water doesn't arrive reasonably soon, the tree becomes stressed,
and if the water shortage goes on for more than a short time,
the tree can be badly knocked back in its growth, or even die,
as the confined fibrous root system dries out, sometimes
beyond repair. To compensate for this, growers choosing drip
irrigation will need to have many drippers placed at intervals
of one metre or less along both sides of the tree row. While
this wastes water when the trees are young, it is an economical
way of watering when the trees are mature.
If
you start irrigating with single or double drippers, after
about one year (more or less), it is important to consider changing
the drip irrigation to under-tree sprinklers. This
encourages the roots to form a wider, stronger, more stress-free
base for the olive tree to stand on.
Here
we are going to talk about the use of under-tree micro-sprinklers.
Firstly,
don't skimp on costs by using a cheap inadequate filter
to feed water to your micro-sprinklers. You will regret
it. Insects are often blamed for the blocking of drippers and
sprinklers when more often the real culprit is an inadequate
filter system. Disc filters are more expensive than the cheaper
strainers but if you don't fancy wasting hours each watering
while you unblock drippers and micro-sprinklers, then
you will be well rewarded by the extra expense.
Secondly,
don't use irrigation lines in your orchard that are so
small that pressure losses are caused at the ends of the lines,
resulting in reduced water application to some trees.
Talk to a reputable irrigation equipment supplier
and don't skimp on their recommendations. If their information
seems unreasonable, then get a second opinion because your dollars
are at stake.
Thirdly,
don't use low density poly piping for your lateral lines
that feed the water along the tree rows. The soft walled
piping can easily be crushed by the strong, ever-thickening
olive tree roots. As a result, the trees further down the line
from where the restriction occurs will not receive enough water.
Use the stronger walled agricultural grade class "B"
black poly pipe and bury it 75 to 100mm (3-4 inches) deep along
the tree row. This way it will be deep enough not to get
damaged by passing machinery and yet shallow enough for you
to easily access the sprinkler insertion point.
Now
we get to the type of micro-sprinkler which has been designed
specifically for olive trees. It is simply called The
Olive Sprinkler
and is in the Waterbird® sprinkler range produced
by Irritrol. (Waterbird® V1-PC)
The
Olive Sprinkler is specially designed for under-tree
watering and delivers an even amount to every tree regardless
of whether the trees are growing on flat or hilly land.
It
is not sensible to use a sprinkler that produces a fine mist
because much of that mist can be wasted into the air and therefore
not used where the water is needed, at the tree's roots. The
Olive Sprinkler produces a reasonably large water particle and
therefore very little of the water is wasted. For growers
in areas where high winds can be experienced during watering,
the 47 litre per hour olive sprinkler may be best as it has
quite large water particles.
Regarding
the built-in flow compensation facility, without this
device, trees higher up the hill would receive less water than
trees at the base of the hill where the water pressure
in the line is much greater. With these flow-compensated
sprinklers, as long as the water pressure variation in the lines
stays anywhere between 1.2 and 4.0 bar (18 and 60 psi), then
each tree, regardless of its position on the hill, will
receive the same amount of water.
If
you have a low water pressure, or a pipe size that is too small
to carry a larger volume of water, or a soil surface that does
not allow the water to soak in quickly, then a very
low flow nozzle may be needed. incidentally, using
a suitable straw mulch on hard-setting soils will improve
the water penetration of these soils and also decrease compaction
problems caused by water droplets hitting the soil surface.
Mulched soil will need more water to initially penetrate the
mulch and fully water the root zone.
Nevertheless,
once the water has penetrated the mulch and soil, the
mulch then protects the soil from drying out for a much longer
period of time than if the soil had not been mulched.
The mulch also benefits the tree by reducing the weed
growth, keeping hot soils cooler in the summer and encouraging
the beneficial action of earthworms and other micro-organisms.
If
on the other hand you have a plentiful water supply and pressure,
and your soil will quickly accept a larger volume of water without
it being wasted in run-off, then a larger capacity sprinkler
such as the 47 litre/hour one may be able to be used to good
advantage.
One
point before we go on - you should be able to get professional
advice on your personal irrigation design from a local irrigation
firm. Also, The Olive Sprinkler complete with its nozzle, swivel,
snap off deflector, pressure compensating device, solid UV stabilised
plastic stake, feeder tube and barbed fitting for plugging
into the main polythene water line (what a mouthful!),
should only cost you about $2.50 all together at
today's prices.
Now
the next very important benefit of The Olive Sprinkler is
the snap off deflector. We're going to discuss
how to use this sprinkler so that water is not wasted.
For
the first stage of watering, the tree is small and the
water spray pattern only needs to be very small in diameter.
How do we achieve this? About 150 - 200 mm (6 - 8 inches)
beside where the tree is to be planted, push a 15 - 20 mm (3/4
inch) diameter steel spike into the ripped soil to a depth
of about 300 mm (12 inches). Pull the spike out and now
it will be very easy to push the sprinkler stake almost to its
full depth into the soil. The actual sprinkler head on the top
of the stake will now be only 50 - 75 mm (2 - 3 inches) above
the soil. The two stage swivel has the deflector in place
which deflects the water down towards the ground and covers
a total diameter of 750 mm (30 inches). This is ample
for the first 12 months of root growth and each watering will
only take a short time (15 minutes will deliver about
9 litres (2 gallons) with the 35 litre per hour sprinkler).
Watering
for one hour will apply 35 litres (8 gallons). Depending
on the soil type, regularity of watering and whether mulch is
being used or not, one hour will probably be more than
ample for the tree at one to two years of age.
Stage
two requires that the stake be removed from its almost buried
position and re-pushed into the soil nearby to its normally
designed depth of about 125 mm (5 inches). With the spray now
higher in the air, the water will spray to a total diameter
of about 1.5 metres (5 feet).
For
the third stage of watering, snap off the little plastic
deflector to allow the water to spray slightly upwards so that
a ground diameter of about 4.5 metres (15 feet) will now be
watered, which will be suitable for the rest of the life of
the tree.
All
of the above three stages occurred without changing to a different
sprinkler. The Olive Sprinkler is suitable for irrigation
from the day of planting onwards.
Incidentally,
the red 'fire stake' is ultra-violet (UV) stabilised
for long life and is very easy to see in your orchard thereby
reducing ant possible damage from tractors, slashers etc..
One
last point - to fit the barbed fitting into your main water
line that runs past the tree, carefully pierce the pipe with
a suitable spike or special tool supplied by the irrigation
shop. To make it easier to insert the barb into the reasonably
tight hole in the water line, you may need to hold the
barb fitting firmly but gently with a pair of pliers to be able
to apply the pressure needed to push it in.
Well,
if you can find a better method of irrigating your trees then
please let us know as we're always looking for useful improvements
for the industry.
Happy
irrigating to you.
