Chapter 20

Fertigation in Greenhouse Production

Pressure Differential Tank Fertigation Injection

A pressure differential tank system operates on the principle that a pressure differential is created by a partially closed valve placed on the pipeline between the tank inlet and outlet (Figure 20.2). The pressure difference forces the water into a bypass pipe, where it enters a pressure tank containing the fertilizer. The irrigation water mixes with the fertilizer solution, and the dilution passes out of the tank into the downstream irrigation system. A metering device often controls the flow back into the main line. Care must be taken to ensure sufficient time is allowed for the fertilizer to dissolve and gradually move into the supply line. Most systems require about 40 to 90 minutes of injection time to adequately dissolve and flush out the lines.

Tank Operation

A differential pressure fertilizer tank consists of a fertilizer tank, inlet and outlet pipes, and control valves. It can be connected to the main irrigation pipeline via a branch pipe to mix water and fertilizer. Fertilizer is placed in the tank via an opening with a lid that can be securely sealed. A partial obstruction (e.g., a valve or a filter) installed in the irrigation line causes a pressure differential that pushes some of the irrigation water into the tank. The mixing process is completely decoupled from the distribution process, allowing a dilute solution to be removed from the tank at practically any flow rate without affecting the concentration accuracy.

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