Semiautomatic irrigation systems can be time-saving for large greenhouse operations. Most are designed for bench production, but systems for potted plant production also exist. The systems are designed to apply a standard amount of water to a crop. By linking the system to appropriate controls, several benches or crops can be watered in succession. However, the grower must still determine the frequency of irrigation and the amount of water to be applied. The system must be checked frequently to ensure that no nozzles are clogged and that no leaks have developed in the pipes or tubes.
The semiautomatic systems may be directed spray systems, trickle systems, or ebb and flood systems. Spray systems deliver the water through nozzles spaced at intervals along the pipes, which run around the perimeter of the greenhouse bench. Trickle systems deliver the water through holes in inflatable plastic tubes stretched down the bench (Figure 20-11). A form of trickle system is used for potted plants.
figure 20-11. A semiautomatic irrigation system used in a ground bed for watering roses. Note the control valve, the pipes along the side of the bed, and the ooze tubes crossing the bed at intervals. (Delmar/Cengage Learning. Photo by Jack Ingels.)
figure 20-12. A trickle system delivers water to each pot on this bench. As seen here, the nicknamed "spaghetti system" is understandable. (Delmar/Cengage Learning. Photo by Jack Ingels.)
Nicknamed the spaghetti system, it delivers water through thin plastic tubes attached by pins or weights to the pot on one end and to a three – quarter inch PVC pipe on the other end. The PVC pipe runs the length of the bench to transport the water (Figure 20-12).
Other forms of trickle systems include ooze tubes and water loops. Ooze tubes are plastic tubes that are rolled out in rows between plants growing as bench crops. Water seeps from the tubes through small holes at intervals along its length. Ooze tubes are especially important where water conservation is needed since they deliver water in low volumes (Figure 20-13). Water loops are used for irrigating container grown plants. They are small rings of plastic that are placed around the base of each plant within its container. A header carries the water to each container where it trickles from the loop onto the media surface. Like all trickle systems, the water loop is a low-pressure delivery system.
Not quite fitting into the category of trickle systems is the capillary mat, most suitable for the production of potted plants that should not have wet foliage. This mat is made of fibrous material and is placed on a bench that is first lined with plastic (Figure 20-14). Water and nutrient solutions periodically flood the mat and are then absorbed by the plant through capillary action. The mat system is also useful for the production of plants in pots of various sizes. The system has the disadvantages
figure 20-13. Ooze tubes deliver low volumes of water across the bench. (Delmar/Cengage Learning. Photo by Jack Ingels.)
figure 20-14. Capillary mat showing the plastic liner (Delmar/Cengage Learning. Photo by Steven Newman.)
of becoming unsightly due to algal growth and harboring insects and pathogens within the matting. Periodic sterilization of the mat and bench is needed.
Ebb and flood irrigation does not trickle; it floods. Water is pumped from a storage tank into a water-tight bench where it flows across the surface, flooding the entire bench. After about twenty minutes, the liquid is drained back into the storage tank for reuse. An ebb and flood system permits water soluble fertilizers to be applied concurrent with watering. The system is used for pot crop production in both raised
figure 20-15. Ebb and flow irrigation floods the bench, then drains back into a storage tank. (Delmar/ Cengage Learning)
benches and in greenhouses where crops are grown directly on the floor. Since all pots receive the water at the same time, they absorb an equal volume of liquid. The system is monitored and controlled by computer (Figure 20-15).