YOU WANT WET PLANTS, NOT SOAKED PLANTS
how much to water on basic observation of
the moisture status of the substrate. These
may include visual clues such as the color
of the substrate surface, which for many
may be darker when moist and lighter
when dry, or a finger test to determine how
moist the substrate feels below the surface.
These methods are largely based on experience with different types of growing
substrates and can be difficult for people
new to soilless growing.
Another method, which is more accurate
and commonly used by commercial greenhouse growers, is to collect and measure
the volume of leachate after each irrigation. Leachate refers to the nutrient solution
draining from the base of the growing slabs
or containers. Most commercial growers
aim for a five to 20 per cent leachate/drainage volume at each irrigation, that is five
to 20 per cent of the volume of irrigation
applied to each plant drains from the base
of the container, bucket, bag or bed. If the
drainage volume is higher than this, the
irrigation time is cut back. If it is lower, it
is increased in volume and/or frequency.
Using the drainage volume measurement
method is particularly effective in drip irrigation indoor gardens as the growing environment is less prone to daily changes in
sunlight, humidity and temperature, which
determine irrigation requirements.
Coconut fiber can retain high levels of moisture between irrigations.
“
Small drip irrigation systems in particular are
prone to using under-pressurized pumps, which
can lead to poor flow rates.”
Along with monitoring of leachate volume to help adjust
irrigation programs, basic system checks are vital with
indoor gardens. Small drip irrigation systems in particular
are prone to using under-pressurized pumps, which can lead
to poor flow rates, increased occurrence of blocked drippers/
emitters and uneven amounts of nutrient delivery around
the system. Using a jug to collect and measure the volume of
nutrient solution coming from each dripper in the system is
an important process to ensure all plants receive the same
amount of irrigation. Growth differences between plants in
the same system are often found to be attributed to uneven
irrigation volumes in drip-fed systems.
Advanced Methods of Irrigation Control
There are more advanced automatic irrigation control
methods to take note of. These methods involve measuring the moisture status in the substrate, which then triggers
nutrient application accordingly. These include the use of
substrate moisture sensors or irrigation devices that weigh
the substrate to determine moisture loss. Other methods
commonly used in commercial greenhouse production are
solar integrators linked to irrigation controllers that base
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Maximum Yield USA | October 2016