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Plants need water to grow, and although this is obvious to any farmer or gardener, water availability is the limiting factor to plant growth more often than most realize. More and more growers have become aware of this and are installing irrigation systems.
Once the decision to spend the time and money getting water to your crops is made, then you have to decide between two basic system designs. Are you going to spray water over the tops of the plants like a rain shower or drip water into the soil?
Drip irrigation is accomplished by laying what looks like very thin-walled hose, called drip tape, either on the surface or slightly buried in the soil near plants. Sometimes drip irrigation is called trickle irrigation, because tiny holes in the drip tape allow water to trickle out slowly. Drip irrigation systems are more expensive to purchase than overhead sprinklers and may be much more time consuming to set up. So why are many farmers and gardeners turning to drip? Because it benefits the plant, the environment and maybe the farmer’s bottom line, too.
A properly installed drip system reportedly uses up to 50 to 80% less water than overhead systems. Since water is applied only to the area around plants, much less is wasted on ground that is growing nothing but weeds, and much less is lost by evaporation and weed transpiration. Even more conservation can be attained by laying the tape under a mulch. Since much less water is used, much less is needed, and smaller water systems are adequate to irrigate fields. Drip irrigation is done with very low water pressure, so pumps do not have to be large. Also, less energy is used to pump water.
Drip irrigation helps avoid diseases, because it doesn’t wet the leaves. Fungal spores need hours of leaf wetness to germinate. Sometimes long periods of moisture are unavoidable due to the weather, but overhead irrigation often compounds the problem. Also, since drip gives you a high degree of water control, plants can be supplied the precise amount of water they need, row by row. Puddles and plants standing with wet feet can be avoided.
Another advantage to drip is that you can continue to work in the field or garden while it is being watered. Also, you can water very hilly terrain without worrying about runoff, and you can water on very windy days.
Overhead irrigation may begin to sound like a thing of the past, but drip has some disadvantages, too, and in some places drip cannot do what overhead can. For example, drip irrigation cannot be used for frost protection (see my article on frost in the Fall 2004 issue of The MOF&G). Drip tape must be laid close to plant roots, and laying so many lines would be impractical in some systems, especially in crops such as grains and alfalfa. Sometimes rodents chew on the tape and get water. But read on if drip irrigation still sounds like a good choice for you.
Here is a basic design for a drip system for gardens and small agricultural fields. If you want to learn more or think you need an elaborate system, I have included some good references at the end of the article.
The diagram shows the basic components of a drip system. The water source has to match the amount of water needed for the size of your system. The suppliers I list at the end of the article can help you decide how much water you need once you tell them how much line you are going to put out. You can water gardens and small hoophouses from a good household well, but if you are watering acres, you will need a larger water source, of course. For example, vegetables planted in rows 6 feet apart and irrigated with tape that emits 0.52 gpm (gallons per minute) per 100 feet of tape would require 38 gpm/acre.
Drip tape has tiny holes that can clog easily, so the cleaner the water, the better. Wells and municipal water sources are usually good. Surface water, such as that from ponds and streams, is not recommended for drip systems. Even with good water sources, a filter is used in line.
Pressure regulators help maintain a constant pressure as the water flows through the system. Otherwise, the tape can burst by sudden large increases in water pressure.
Water is pumped to the field through a hose and is spread evenly across the end of the field using a header. The header can be made of lay-flat hose, or, in hoophouse systems where no traffic drives over it, rigid piping. Each row of crop gets a line of drip tape. Locking fittings connect the tape to the header and come in many types, depending on what you need for your header. Some types punch into lay-flat hose, the tape fits over the other end, and a collar screwed over the tape holds it tight.
Because of variation in pressure, tape is rarely laid out longer than 400 feet – a consideration when deciding where to place feed lines and headers. The tape should be as close to the plant as practical and no more than 12 inches from the plant row. Most tape is placed no more than 6 inches from the row.
Drip tape can be laid on the soil surface, especially if it’s laid under black plastic mulch. The disadvantage to laying it on the surface (without mulch over it) is that more water evaporates, and workers, wind or animals can damage it. Drip tape is best buried about a few to 6 inches deep.
The following sources of drip tape irrigation systems and supplies have excellent catalogs with much more information on how to set up systems. All can offer technical assistance, so call and see what they offer. Also, don’t be afraid to jerry rig a system yourself. You’ll be surprised at what can work.
Suppliers of Drip Irrigation
119 Bridle Road
Antrim, NH 03440
Charles W. Harris Co.
451 Old Somerset Ave.
N. Dighton, MA 02764
Harmony Farm Supply
P.O. Box 460
Graton, CA 95444
190 Sanhedrin Circle
Willets, CA 95490
Carter, Ann and John Howell. 2000. An Overview of Drip Irrigation. University of Massachusetts Cooperative Extension.
Ross, D.S., R. A. Parsons and H.E. Carpenter. 1985. Trickle Irrigation in the Eastern United States. Northeast Regional Agricultural Engineering Service. NRAES-4. Cooperative Extension, (607) 255-7654; Fax: (607) 254-8770; PO Box 4557, Ithaca NY 14852-4557; [email protected]; www.nraes.org.
Hansen, B., L. Schwankl, S.R. Gattan and T. Prichard. 1994. Drip Irrigation for Row Crops. University of California Irrigation Program, UC Davis. Order from Cooperative Extension Office, Dept. of Land, Air and Water Resources, 113 Veihmeyer Hall, Univ. of Calif., Davis CA 95616; 530-752-1130.
About the author: Eric is MOFGA’s director of technical services and can answer your farming and gardening questions at [email protected] or 946-4402.