Chapter 18

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 an injector, a chemical supply tank for concentrated stock solution, backflow prevention devices, filters, pressure gauge, and a water meter. Depending on the types of injector additional equipment (valves and pressure and flow regulators) may be required. 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. Injection equipment should be located downstream of the pump.

Chemical Injectors

Fertilizer injectors are mechanical devices used to apply water-soluble fertilizers, pesticides, plant growth regulators, wetting agents, disinfectants, and mineral acids during crop production. They are a vital part of modern vineyard operations. Since the introduction of injectors or proportioners, growers have enjoyed an easy, time- and labor-saving method of applying liquid chemical solutions to their crops.

Pressure Differential Tanks

Pressure differential tanks, often referred to as “batch tanks,” are the simplest of the injection devices. A differential pressure 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. The pressure difference forces the water to enter through a by-pass pipe into a pressure tank which contains the fertilizer. The irrigation water mixes with the fertilizer solution and the dilution passes out of the tank into the downstream irrigation system.

Venturi Injectors

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. The injection rate of a venturi device is determined by the size of the venturi and the pressure differential between the inlet and outlet ports. The larger the pressure drop, the higher the injection rate, up to some maximum drop.

Metering Pumps

Pumping is the most versatile and accurate method for injecting chemicals into micro-irrigation systems. Positive displacement pumps or centrifugal units are usually used. Positive displacement pumps are very good because they can be accurately metered. The pump draws the fertilizer solution from a stock tank and injects it by positive displacement into the irrigation line. Both electrical and water powered positive displacement pumps are available.

Chemical Supply Tank

The stock tank should be large enough to allow the entire fertilization job to be completed with one batch of fertilizer concentrate. A large stock tank is needed if low injector ratios are used and if the injector is used frequently. A larger stock tank size is beneficial if a constant liquid fertilization program is practiced. Tank size should be large enough to contain the chemicals sufficient for at least one fertigation operation. The size of the stock tank can vary from as small as 5 gallons to as large as 2,000 gallons. If more than one stock tank is in use, each tank should be clearly labeled as to the fertilizer it contains. Stock tanks containing concentrated fertilizer are located near the injector.

Backflow Prevention

Backflow can occur in a system due to cross connection between a water source and an irrigation system. For example, water may be turned off, but the chemical injection unit may continue to work, contaminating the water source. To protect groundwater from chemical contamination, backflow—whether from back-siphonage or back pressure—must be prevented. Back-siphonage is the reversal of normal system flow, caused by negative pressure (vacuum or partial vacuum) in the supplying pipe.

Click on the following topics for more information on fertigation systems for vineyards.