Home' Grower : February 2012 Contents The South Australian Grower -- February 2012
heatwaves to get worse
to limit damage, extend resources
the fruit is routinely used in wine grape production.
The upper leaf canopy of tree crops can ser ve the same
purpose. Growers often bend leaves over to shade cau-
liflowers. Damaged leaves should not be removed as
they will provide better shading than no leaves.
THEY are routinely covered by white wash to part-
ly block out the sun. External retractable shade sys-
tems can be used but are less common due to their
expense and complexity in using them. Internal
shading will protect the plants from sunburn, but
overheating can still result. Glasshouses provide
warmer more humid conditions for plant growth.
However heat gained is dependent upon area, not
volume. A taller glasshouse will heat up similarly to
a short glasshouse but has more space for the heat-
ed air to move above the crop. The trapped heat is
removed by exhaust fans or other types of ventila-
tion systems, which also ser ve to maintain a supply
of 'dry' air for evaporative cooling. Their correct
installation and use is essential for even airflow.
STRATEGY 3: Break the flow of air
PLANTS need some air flow to evaporate water:
Good air circulation is needed to move the water
filled air away from leaf surfaces and replace it with
drier air. However, heatwaves often occur in periods
of strong winds. It is therefore important to slow
down air movement to reduce excessive rates of
water loss from the leaves and give the root system
more chance to keep up with the demand for water.
Physical damage resulting from leaves rubbing
against each other will also be reduced. Air flow is
most damaging when there is nothing blocking the
main pathway of flow. Breaking up the pathway of
flow and forcing air to move through gaps, is the
most effective means of reducing wind speed.
STRATEGY 4: Wind Breaks
THE pressure for maximising available land for
growing the field vegetables and tree crops leaves
little space for planting permanent wind breaks.
Other means of breaking up airflow, include:
Planting the edge rows of tree crops at right
angles to the direction of the main rows of trees;
using shade cloth along fencing; using different
varieties or types of crops in field planting bays.
The different shapes and heights can break up air
flow. Using composted mulch and/or sowing a sec-
ond cover crop to 'protect' emerging seedlings of
carrot and onion. Selective herbicides are used to
spray out the cover crop when seedlings are estab-
lished. Some growers also plant a cover crop between
the bays of carrots or onions to break up air flow.
Both the compost and protective crop will add
valuable organic carbon to the soil.
Reveg-by-design native vegetation borders not
only provide a habitat for beneficial birds and insect
species of common pests and disease, but can used
to provide a wind break. Always maintain vegetative
cover over fallowed soil. Your neighbours will not
like your soil wind blasting their crop.
STRATEGY 5: Automation
USING automatic controllers attached to deci-
sion-making software is used in hi-tech facilities.
Good maintenance, training of operators and reli-
able backup in the event of system breakdown or
loss of power are essential.
If you automate, have a back-up plan.
STRATEGY 6: Monitor, make informed decisions
INSTALL thermometers, humidity, or sap flow
sensors, and soil water monitoring devices in the
crop. They will help you determine if the plants are
potentially suffering a heat related problem and/
or water supply problem, as well as the effective-
ness of cooling and ventilation strategies. Locate
sensors in an area that is representative of the average
crop conditions. Use the information and crop
response to improve your management strategies.
Details: Jeanette Chapman
jeanette.Chapman@epa.sa.gov.au or Anthony Fox
Impact of Stress on Crop Yield and Quality
Time to Harvest, Increasing Total Accumulation of Stress
Salt build up due to excess fertiliser.
Impact of stress on yield and quality.
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