Irrigation in the arid desert is essential for growing plants that are not adapted to this region. Water is a precious resource. Home gardeners and commercial growers are using more technical methods of irrigation. Drip irrigation is the most productive form of irrigation yet devised, reaching 95% efficiency. Drip irrigation is the frequent, slow application of water to the soil or growing media into the plant root zone, drop by drop. Drip had its beginnings in the United States with much of the current technology developed in Israel.
A drip irrigation systems has three components: 1) the head, which includes the water source, system control valve, filter and pressure regulator; 2) distribution system; and 3) the emitters.
The head has three elements, the first being a water source with a valve. The valve could be a hose bib, manually operated valve or an electronic valve connected to a time clock. The second element is a filter which removes fine particles from the water stream so that the small openings on drip emitters will not plug. The filter system can be a simple in-line 120 wire mesh screen type or as complex as a sand filter similar to those used for filtering swimming pool water. The third element is a pressure regulator which will reduce the pressure down to the operating pressure needed by the emitters. City water systems normally have water pressure in the 25 to 60 psi range. Drip systems normally operate on pressures under 25 psi.
The distribution system consists of pipes that form main and lateral supply lines that carry the water to the target area to be watered. The most common pipe used for home gardens and landscapes is made from white PVC or black polyethylene materials. Various connectors are used to adapt the pipe to the emitters.
The emitters are the last and perhaps the most important component of the drip system and insures that plants receive the desired amount of water. There are many different emitter designs but they can be placed in three general categories: 1) point source; 2).linear; and 3) micro sprays. Point source emitters are those that are exactly placed. These include a simple opening that delivers the desired amount of water and are the least expensive. Laminar flow emitters are designed to have a "maze" through which the water flows and then released through a larger opening. The "maze" causes turbulence which prevents particles from blocking the emitter opening. Diaphragm or compensating emitters are also available which adjust internal pressure and therefore external output. These allow for the same distribution pattern over uneven terrain or long lateral runs. Many also flush at the beginning and end of each irrigation. These are installed as needed usually by punching a small hole in the tubing and then inserting the emitter. Mistakes can be corrected by putting a "goof plug" in the unwanted hole. Linear emitters are placed by the manufacturer in tubing at pre-set spacings and are difficult to change. The emitters in linear tubing can be simple openings, laminar flow, pressure compensating or others. This type of tubing is generally used where rows of plants are established, the length of the tube is determined by the installer and is cut off of the roll of tubing and attached to the lateral line and the ends are plugged. Micro-spray emitters spray a fine stream of water. These can be installed on tubing or placed on stands above the ground to spray an area. There are many designs of micro-sprays, some with moving parts, others with fixed openings. Moving parts have a tendency to wear out and fails over time. Emitters can also be connected to the distribution system by l/4th or l/8th inch tubing-called "spaghetti tubing". Several "spaghetti tubes" can be connected to a multi-emitter which is connected to just one point on the distribution tubing.
An irrigation system should be engineered backwards. This means that the water requirements of the plants must be known and the resulting design should be sized to deliver the needed water. A determination of how much water is available is also needed. To measure the flow rate use a one or five gallon bucket to catch the water and time how long it took to fill up. To calculate the flow rate divide the amount of water caught by the time it took to catch it. If a pressure gauge is available the water pressure can be determined. This is the total potential capacity that the system or zone of a system can have in terms of gallons per minute. Of course with the use of valves, many zones of a system can be run in sequence, but only one zone at a time. The drip system is designed between these two points; namely the water available and the water the plants require.
There are some drawbacks to drip irrigation, however. The initial cost of a system can be more than a conventional system, but the watering efficiency will more than make up for its cost over time. A drip system does take some management, i.e. plugged emitters, salt build-up, broken distribution lines, etc., and if not monitored can result in plant loss. Another disadvantage is if one gets behind irrigating it may be difficult to "play catch-up"
Designing a drip irrigation system is a fun and rewarding activity. Many installations can be completed on a, weekend and, provide worry-free irrigation for an entire garden, orchard, or landscape.
Anyone interested in further information, here is a link for drip irrigation or you can contact the University of Arizona Sierra Vista, Cooperative Extension office at 520-458-8278 ext 2141 or the Master Gardener office ext 2176. If there are enough people wanting to design their own irrigation system, a short class could be scheduled. Please call and leave your name and phone number if you are interested so a course can be organized.