Chapter 20

Fertigation in Greenhouse Production

Proportional Fertigation Injectors

Proportional dosing or injection means that the flow rate of the chemical is automatically adjusted to maintain a target concentration of chemical (or pH) in the irrigation water. If the irrigation water flow rate changes, the chemical flow rate will change by the correct amount in proportion to the change in the irrigation water flow rate. Proportional injection is always automatic.

Advantages of Proportional Fertigation

Some of the advantages with proportional fertigation systems/packages include:

Components of Proportional Systems

Proportional dosing can be achieved in a number of ways. Each manufacturer will offer different components and control techniques with their proportional system. Almost all agricultural proportional systems use electronics. The basic components that are essential to an electronic proportional dosing system are: (1) irrigation water flow meter; (2) some way to directly measure or estimate the chemical flow rate; (3) process controller; (4) chemical injector; and (4) user interface screen/input mechanism to the process controller.

Types of Proportional Injectors

Dosatron Injectors

Dosatron injectors (Figure 20.4). These injectors operate without electricity, using water pressure as the power source. They are installed directly in the water supply line. Water flow activates the injector, which takes up the required percentage of concentrate directly from a container with stock solution. Inside the injector, concentrate is mixed with water, and water pressure forces the solution downstream. The amount of concentrate dispensed is directly proportional to the volume of water entering the injector, irrespective of variations in water flow or pressure that may occur in the main line.

DosMatic Injectors

DosMatic injectors, acquired by Hydro Systems, operate without electricity and use water pressure as the power source. They are installed directly in the water supply line. Water drives the injector, which takes up the required amount of concentrate directly from a stock tank containing concentrate solution. Inside the injector, the concentrate is mixed with the water, and the water pressure forces the solution downstream.

Gewa Injectors

Gewa injectors have no suction or pumping device. The concentrated fertilizer solution is forced into the waterline by the water pressure. The fertilizer concentrate is poured inside the injector into a plastic membrane suspended inside the tank, and the lid is sealed shut. When the water is turned on, it surrounds the membrane and applies pressure to the bag, which forces a calibrated amount of concentrate into the waterline.

Anderson Ratio:Feeder Injectors

Anderson Ratio:Feeder injectors feature positive displacement and volume proportioning by either a flow metered electric pump or water pressure, depending on the model (Figure 20.5). The original Series S is water driven while the intermediate Series J-Plus are electric units. All units have adjustable feed ratios and can be adjusted while the injector is in use. The design of Anderson injectors permits wide water flow ranges with minimal pressure loss. There are no sliding seals in the pumping mechanism as well as no metal in contact with the chemical (stainless check balls are used with fertilizers and some acids).

Smith Measuremix® Injectors

The Smith Measuremix injectors operate on water power and require no electric motor or gasoline engine. Water passing through the water motor provides the power to run the injector pump. The water motor actually meters the water running through the unit. For every revolution of the water motor, there is one stroke of the injector pump. The proportion of water to chemical solution remains the same, regardless of changes in water pressure. The Smith Measuremix injectors are built to dispense a variety of liquid chemicals.

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