Each irrigation zone can be
controlled by either a manual gate or ball valve or automatically by an electric
solenoid valve. Usually one valve controls one zone. Solenoid valves use a low-voltage
(24 volt) electrical current that actuates a small electromagnet to hold open
the valve. When the voltage is removed the valve closes.
In automated systems, solenoid
valves are activated by controllers that can range from electrical timers to
complex computer systems capable of complex decisions.
Controllers should be
flexible enough to allow several irrigations each day and at intervals of one
or more days or on specified days of the week. Since containers hold a limited
amount of water, cyclic irrigation to apply water two or three times a day may
maintain better substrate moisture without leaching.
Moisture sensors and EC
meters may be used in conjunction with controllers to to achive more sophisticated water application
control in a nutrient management scheme.