Deficit Irrigation and Increased EC
Deficit irrigation is a widely used practice
in horticulture. It’s particularly useful
in soil-based systems, but it also has
application in hydroponic systems
for certain crops. Deficit irrigation is
the careful restriction of water flow so
that plants experience slight moisture
stress. While this has several physi-
ological effects on plants, it is largely
practiced to enhance the compositional
quality of fruits like tomatoes or grapes.
With restricted water uptake, more sugars
and other compounds concentrate in
fruit tissue, thus giving an improved
flavor profile. In herbs, this prac-
tice can also result in higher levels
of volatiles, which contribute to their
distinctive flavors and aromas.
The issue with deficit irrigation in
hydroponics is it requires a high degree
of control and grower skill to ensure
plants are only mildly stressed and not
permanently damaged, which would
result in a significant loss in yield. It
requires substrate moisture sensors
and continual adjustment of the irriga-
tion program as the plants develop. An
alternative method of applying mild
plant stress is to increase the electrical
conductivity (EC) of the nutrient solu-
tion. This technique also restricts the
uptake and accumulation of water
by the plant, but it’s much easier
to maintain than a certain level of
deficit irrigation. It’s already a well-
used tool in tomato production.
A high EC during fruit formation
maintains crop quality under low winter
light conditions and improves the fruits’ brix
levels and flavor profiles year-round.
Apart from improvements in fruit quality, deficit
irrigation and higher EC are also used to steer
crops away from being overly vegetative and
towards being more generative (producing more
flowers and fruits). To achieve deficit irrigation in
this situation, growers could reduce the volume of
nutrient solution applied at each irrigation, allow
more time between irrigations, or allow the medium
to dry slightly overnight by restricting early morning
and evening watering, among other options. No
matter the method, however, using deficit irrigation
and higher EC to force plants into generative growth
must be exercised with caution. Too many moisture
fluctuations in the root zone can lead to an increase in fruit
problems such as blossom end rot and the fruit splitting under
certain growing conditions.
“
COMMERCIAL HYDROPONIC
growers commonly use root
zone manipulation techniques
to achieve specific goals.”
Volume Control
Hydroponic crops experience some degree of root volume
restriction, while most plants grown in soil do not. (For
example, a field-grown tomato may average more than
200 liters of rooting volume per plant thanks to its almost
unlimited access to soil depth for foraging water and nutrients.)
Top: Root zone controls, such as deficit irrigation and elevated EC
solution levels, are used to control fruit quality in hydroponic tomatoes.
Bottom: Root tissue sends non-hydraulic messages to the shoot,
which influences plant responses.
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