Adequate filtration is an essential and often expensive component of a drip irrigation system in order to prevent plugging of emitters. Permanent commercial applications typically utilize large sand-media filters which periodically clean themselves via backflushing, while temporary set-ups may utilize less complex apparatus with screens which can be removed and cleaned.
Three types of apparati are typically used to inject fertilizers and chemicals into drip irrigation systems. The point of injection usually follows the filter system and a one-way apparatus to prevent accidental contamination of the irrigation source. Concentrated product is added to a differential pressure tank and then diluted over a period of time during the application. Water from the drip line enters one end of the device, mixes with the product inside, and exits from the other end back into the drip line. As a result, a concentrated solution is applied at the beginning and a dilute solution at the end. Depending on the product applied, there is a greater potential for phytotoxicity to occur with this type of device than with devices which provide a more uniform application.
The rate of flow of water through a venturi apparatus (black device in U shaped offshoot of irrigation line) creates a suction which draws concentrated product from a container into the irrigation line. If pressure is held constant, the rate of injection is relatively constant throughout the application process.
With each stroke, an electric A piston pump draws up a calibrated unit of product and injects it under pressure into the irrigation line.
Drip irrigation tubing can either be laid on the surface of the ground as in this orchard situation, or buried beneath the surface, as in this permanent set-up. In most cases, nematicides are injected into the same drip tubing which will be used to irrigate a crop. Portable devices have been developed with reels of drip irrigation tubing which can be temporarily laid out in a field to apply nematicides and then reeled up for use in another situation.
The spacing and flow rate of drip emitters are chosen to provide optimum distribution of water in a particular soil type and for a particular crop. In sandy soils (drawing on right), water will typically move deeper more rapidly than it will move laterally. In heavier soils (drawing on left), water will typically move laterally more rapidly than it will penetrate. Generally, the same factors that contribute to optimum root coverage for irrigation of a particular crop will contribute to optimum distribution of a nematicide throughout the root zone if the nematicide is applied over most of the irrigation period.
A large Arizona operation has developed what is considered the optimum system for farming with permanently buried drip irrigation. One filter system and chemical injection site is used for four surrounding 20 acre parcels. Special equipment has been developed for burying 20 acres of tubing a day and for tillage without disturbing the tubing. Cotton, wheat, watermelons and tomatoes are the primary crops grown with this system.