Micro-Irrigation for Greenhouse Crops
Chemigation Injection
Most greenhouse operations are going to want to have their micro-irrigation system set up for chemigation (applying fertilizers or pesticides through the irrigation system) (Figure 17.9). Chemigation requires a number of large tanks to hold the chemicals that are to be injected (usually in liquid form), a pump, and an injection port that mixes the chemicals with the water. Injection equipment should be located downstream of the pump. For chemigation/fertigation the following must be installed on the water line in following order from the pump—a vacuum relief valve, a low-pressure drain, a low-pressure switch (this shuts the chemical injection pump off if the water pump stops), a functional check valve (back-flow prevention device), and the chemical injection port where the chemical is mixed with the water.
Acid Injection
Highly concentrated acids and other corrosive chemicals are commonly injected into micro-irrigation systems. The components of the injection system, such as tubing, gaskets, and fittings, should be made from suitable materials. While PVC and other commonly used materials are highly resistant to diluted acids, concentrated acids can degrade them over time. Chemicals should be injected into the center of the water flow in the mainline or in a mixing chamber so that the chemical will be diluted before it makes contact with the inside wall of the pipe. Tubing and fittings made from polyvinylidene fluoride plastic will be resistant to concentrated acids and other chemicals used in irrigation systems. Caution: Never inject acid into aluminum pipe.
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