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<pre>Of course everywhere has their own particular conditions but could someone
possibly tell me how important is irrigation in the scheme of things.
having seen both trees as far as the eye can see and small groves
Cheers William McNab.
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<pre>The following is an article re irrigation to vines, relevant to all
crops. I have copied it onto this email as previous posters references
to articles are usually in some esoteric unobtainable publication
usually requiring some form of cash subs.

Roger Farquhar Hunter Valley



"Vignerons offered better ways to water

There is room for improvement in the way Australians water their crops,
says Dr Elizabeth Heij, Adelaide-based Chief of the CSIRO Division of
Horticulture.

"Better management is the first big area that we’ve got to tackle," Heij
says. "We could make probably a third or a half reduction in the amount
of water used just by management alone. There’s considerable wastage."

Heij says work carried out in her Division and overseas shows how
plants cope with water stress. A collaborative project, funded by the
Grape and Wine Research and Development Corporation, between CSIRO’s Dr
Brian Loveys and Peter Dry from the University of Adelaide has shown
that these mechanisms can be employed to boost the efficiency of water
use by plants.

Loveys and Dry started out trying to reduce vigour in cool-area
grapevines. Excess vigour produces too many leaves. These shade the
fruit, affecting its quality. They can also make disease control more
difficult, and reduce yields in subsequent years.
Their research focused on understanding the hormonal mechanisms that
control vine growth, and hence, vigour. Previous work had shown that
photosynthesis and transpiration in vine leaves was controlled by the
plant hormone abscisic acid (ABA). The role of this compound in
controlling vigour therefore came under scrutiny.
Increased concentrations of ABA in the leaves causes the stomata to
close, preventing further leaf gas exchange. Stomatal closure can also
result from increased ABA concentrations in the sap that carries water
and nutrients from the roots to the shoots. Once the hormone has
delivered its message, it is broken down in the leaf into inactive
compounds. The normal, or ‘steady state’ concentration of ABA in shoots
is determined by the balance between import from the roots, synthesis in
the leaves and metabolic breakdown.
Given this relationship between ABA and photosynthesis, Loveys and Dry
speculated that increased ABA production may reduce vine growth, and
that the ABA could be manipulated by using irrigation techniques to
create wet and dry roots on the same plant.
To test their idea, they tried watering only half of each vine’s root
zone. Vine cuttings were sawn in half longitudinally at their base, and
each root system planted in a separate pot. The performance of these
vines was then compared with that of fully-watered and unwatered vines.
Within a few days, the leaf gas exchange, photosynthesis and growth of
both the half-watered and unwatered vines had slowed compared with the
fully-watered ones. But their overall responses were not the same.
Unlike the unwatered vines, the leaves of the half-watered ones did not
wilt. Their water status actually remained similar to that of a
well-watered plant. Thus it was possible to separate the physiological
effects of water stress from the potentially damaging physical effects
such as loss of leaf turgor (wilting) and shoot death.
Loveys and Dry believe that a chemical signal (probably ABA) is
transmitted from the drying roots to the shoot, triggering the
reductions in leaf gas exchange and growth. At the same time, however,
the water status of the vine is maintained by the other half of the root
system which has been fully watered.
"You’re tricking the vine into thinking that it’s water stressed, but
it’s not," Loveys says. "There’s no penalty in terms of yield. We’re
actually making the vines much more water-use efficient."
Having shown the effect of partial root drying in potted plants, Loveys
and Dry applied a number of wetting and drying cycles to the roots of
field vines grown with their roots separated by a plastic membrane. The
irrigation was planned so that one root system received normal
irrigation for about two weeks while the other was allowed to dry. Then
the situation was reversed.
The effect on vine vigour was dramatic, with pruning weights being
reduced by about 29% and number of lateral shoots by 47%. A more open
canopy with better bunch exposure was produced and there was no
significant effect on yield or fruit quality.
Loveys and Dry believe the plant growth mechanisms observed under trial
conditions will also occur in vines grown under normal irrigation
regimes. For example, under drip irrigation, roots outside the normally
wetted zone will become dry and capable of transmitting a signal to the
canopy. Water applied by furrow irrigation may reach a different
proportion of the roots on different occasions, especially if water is
applied to alternate rows, resulting in a varying proportion of wet and
dry roots.
Loveys believes the technique could be adapted to help boost water-use
efficiency in other irrigated crops that have extensive root systems,
such as irrigated pome and stone fruit. In the meantime, irrigation
systems that can be readily adopted by growers are being developed.
These will encourage the grapevine’s own hormonal mechanisms to control
of vigour in a reproducible manner.

Sub-surface savings

Research by Peter Clingeleffer from the Division of Horticulture’s
Merbein office in Victoria is also helping horticulturists to irrigate
efficiently. He started out, with funding from the Dried Fruit Research
and Development Council, to test a new irrigation system.
Clingeleffer replaced open irrigation furrows with slotted agricultural
pipe buried about 15 centimetres underground. With his sub-surface
system, and careful selection of root stocks, clones and trellis, he is
looking to quadruple water-use efficiency.
"We’ve had five seasons, and we’ve got some pretty nice figures there,"
he says. "The implications of what we’re finding are much wider. There’s
a lot of grower interest."
Supporters of Clingeleffer’s system are Brian and Mick Cox of Red
Cliffs, just south of Mildura in north-western Victoria. The Coxes grow
sultana grapes for the dried-fruit market (and some mandarins) on their
30-hectare property which, until last year, was irrigated with the
flood/furrow system.
In 1994, Brian and Mick sought alternatives to furrow irrigation because
it was too labour-intensive. They investigated switching to a dripper
system, but were deterred by the hefty installation cost of $4400/ha. At
only $1210/ha, Clingeleffer’s sub-surface system was more affordable.
Since going ‘sub-surface’, however, the Coxes have saved water as well
as money, and lifted the overall efficiency of their vine-management.
"We used to use all of our annual 275-megalitre water allocation," Mick
Cox says. "But with the sub-surface system, this past season we used
only 119 megalitres."
"In saving water, we’re saving money because if we don’t use all our
water rights, we don’t have to pay for the whole allocation. We would
have had to spend an extra $6000 if we were still relying on the furrows."
Other advantages of the sub-surface system according to the Coxes, are:

* its adaptability to the existing supply infrastructure;
* no need for filtering or backwashing ;
* less water leaching and evaporation;
* existing furrow system can still be used;
* the vines can be accessed from tractor to apply sprays while
irrigating or after rain;
* no pumping cost;
* no more need for cultivation;
* less tractor time and less labour (two to three weeks a year)
required; and
* water can be regulated more efficiently.

Already Clingeleffer is wondering what other crops his system may work
for: wine grapes, probably, and perhaps citrus and ‘row’ crops such as
tomatoes and asparagus. He says one big advantage is that growers don’t
need to change over their whole system at once: they can test it on part
of their block first.
"We know the future of the dried-fruit industry relies on efficient
water use, efficient use of labour and efficient use of our other
natural resources," Clingleffer says.

David Mussared and Bryony Bennett

© CSIRO 1996-2000"

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<pre>back to my pet foibles,

The recent posting on irrigation in Perrugia by J Archer of Olives Aust
(nothing personal) only illustrates the degree to which a little
information can be extrapolated to a larger degree. To my mind to have a
measured quantity of water set against a general quantity of environment
( medium soils, dry summer) makes the data at least irrelevant. As for a
control?


There have been many studies on plant vigour eg
http://www.goodfruit.com/Sept-99/special8.html
where they conclude that "In summary then, the level of water stress
experienced by individual trees over the course of the growing season
may be quite different, even when the trees are under the same
irrigation conditions."

People can't seem to connect that, on its own, more water does not
necessarily equate to better production. Irrigation is not a panacea
for low production or quality. Water places a significant, but not
exclusive role to plant vigour. Why soil biology or soil science is
never mentioned remains a mystery to me.

Roger Farquhar

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