Fertigation Systems for Vineyards
Fertigation System Components
For any fertigation system (See Figure 18.1), the basic components, in addition to the irrigation system, include a chemical supply tank, an injector, a filter, a pressure gauge, check valves, and pressure relief valves. Any equipment that comes in contact with chemicals, including hoses, seals, and gaskets must be resistant to all formulations being applied. This includes emulsifiers, solvents, and other carriers as well as the active ingredient.
Chemical Supply Tank
Supply tanks are usually made of polyethylene or fiberglass because of their potential corrosion. Tank size is an important consideration for a fertigation system. Tank size should be large enough to contain the chemicals sufficient for at least one fertigation operation. Some growers locate the tanks within chemical containment structures in the event of a spill.
Chemical injectors can be divided into pressure differential methods and positive displacement pumps. Pressure differential methods such as pressure differential tanks and venture-type suction devices require some degree of system pressure and a pressure differential to operate.
Differential Pressure Tanks
Differential pressure tanks, often referred to as “batch tanks,” are the simplest of the injection devices. A pressure differential tank system is based on the principle of a pressure differential created by a partially closed valve, placed on the pipeline between the inlet and the outlet of the tank.
Venturi-type Suction Devices
The venturi injectors creates a pressure differential that forms a vacuum. As water flows through the tapered venturi orifice, a rapid change in velocity occurs. This velocity change creates a reduced pressure (vacuum), which draws the liquid to be injected into the irrigation system, eliminating the need for a separate chemical injection pump.
Positive Displacement Pumps
Positive displacement pumps inject at a constant rate regardless of flow or pressure changes in the system. Positive displacement pumps are available in two basic arrangements: piston and diaphragm.
Backflow prevention devices must be installed in both the main system line and injection pump line to prevent accidental backflow of fertilizers into the water source. If backflow prevention devices are not installed, contamination of the water source is very likely if power is lost or the system breaks down during fertigation. Depending on the water source, different backflow devices might be required. Also, if the system is going to be used to inject pesticides, certain EPA backflow requirements must be met. A backflow prevention assembly consists of the following devices:
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