An Introduction to Drip Irrigation Lyndon K. Almand Brazos County Master Gardener Association Introduction Everyday it becomes more important to use our water resources wisely. As the population increases and is more concentrated, demand for water often strains existing water supplies. At the current time in Texas we are using water at a faster rate than the recharge rate of the state s aquifers. In one Central Texas urban area 60% of the energy used by the city is for the water department, basically pumping water. In one large metropolitan area in the state a restriction of watering after 6 pm and before 10 am resulted in a 15% saving of water. Irrigating landscapes uses 25% of the water. Conventional watering systems using sprinklers loose water through evaporation, blown off course by the wind, waste water on non growing areas and often experience run off. Drip irrigation is a very efficient method of supplying water to plants. Sprinkler irrigation is 55-70% efficient whereas drip irrigation is 90% efficient. In drip irrigation water is supplied to the soil surface directly at the plant root zone, drip by drip. Sometimes called trickle irrigation, drip irrigation supplies water close to the soil surface, reducing the chance of evaporation. This slow rate of water flow allows time for the water to soak into the soil resulting in less likelihood of run off. Another advantage is that the water goes right where it is needed, at the plant roots, rather than sprayed all over the plant. Not wetting the plant leaves can also reduce plant disease problems that accompany high moisture levels on plants. Since the water is supplied only to the root zone of plants, open unplanted areas between the plants are not watered resulting in a saving of water and not wasted on growing weeds. The precise placement of the water at the plant root zone soaks deeper into the soil so that irrigation is not needed as often. All of these benefits of drip irrigation can result in better plant quality and a big savings in water use. The simplest form of drip irrigation is the soaker hose, porous pipe and pinhole water hose. These deliver water slowly for a deep soak watering and do a good job within limitations. The water flow is regulated with the turn of the faucet. Often the uniformity of water can vary up and down the length of the hose. Drip irrigation takes the soaker hose concept to another level where the placement and amount of water is controlled more exactly. This control of the water delivery is accomplished with emitters/drippers. The water pressure in a drip irrigation delivery line is reduced from the water supply pressure of 60 PSI or higher to a constant level, typically 10 PSI - 30 PSI, depending upon the emitters used. A basic drip irrigation system has the essential components of a water supply source, such as an outdoor faucet, a supply line for the water and the emitters. Drip irrigation systems can be simple and fairly easy to install by following a few guidelines in the design and installation. Configuration/Layout of a Drip System 1
There are many ways to lay out a drip system. Likely, the main thing to keep in mind is to keep the system as simple as possible and irrigate only those areas where water will be taken up by the roots of intended plants. For shrubs and perennials that are not closely spaced it is probably best to set up a system where the emitters are inserted in drip lines wherever water is desired. In this situation the drip lines are routed close to the base of plants and emitters placed on one or more sides of the plants depending upon size of plant. As a general rule it is recommended that 60%-80% of the root zone be covered in a watering pattern. The soil type a plant is growing in determines the soil wetting pattern. Water flowing from an emitter is distributed in the soil downward by gravity and horizontally by capillary action. The shape of the wetting pattern is dependent upon soil type but can be influenced by tillage and soil amendments. Considering three basic soil types of sand, loam or clay the wetted pattern can be thought of as an oval shape and variations of that shape. In a loam soil the water will move somewhat more downward than laterally and give the classic oval onion shape below ground. Water flows more freely through a sandy soil and has much more downward movement than what moves horizontally. The wetted area from an emitter in sandy soil can be thought of as an elongated shape. A clay soil has finer soil particles and the water tends to move more quickly horizontally than can move downward. The wetting pattern in a clay soil can be visualized as a flattened oval. The coarser textured sandy soils need emitters with higher flow rates so that there would be some lateral movement of water and not an overly deep soaking. Too much downward soaking places water below most of the root zone and is a waste of water. The slower flow rate emitters should be used in clay soils in order to avoid puddling and potential runoff without deep soaking. Soil amendments, such as compost, and proper bed preparation can result in the more desirable soil characteristics and result in a good wetting pattern of sufficient lateral and downward water movement. Plant Grouping- The water needs of plants should be kept in mind when designing the drip system and plants with similar water requirements should be included within the same zone. That is, when a group of emitters are set up for an area the grouping should include plants of similar water requirements. This can be adjusted somewhat if there are larger plants or those which will require additional water by adding additional emitters to the area needing more water. The run time of the system can be adjusted depending upon water needs. If the weather is extremely hot with low humidity, it may need to run a little longer and more often. Likewise if it is overcast and high humidity, the runtime will be shorter and less often. The key is to watch your plants and check the soil to determine when irrigation is needed. A common saying is the most important thing in your garden is your shadow. This applies to no matter what you are growing; you should be out there looking at it, keeping an eye on it. Simply put your hand down and feel just below the soil surface. If it feels dry, water it. Capacity of Water Supply-Each drip irrigation zone is a complete system connected to a water source. More than one zone can be connected to a single water source if there is 2
sufficient water supply. If the supply is not adequate for all zones to be run at the same time, they can simply be run one or so at time. As part of the planning process the amount of water your water source can supply must be determined. That is, how many gallons per hour your system supplies. This can be done using a five gallon bucket; turn on the water supply all the way open and catch the water for a set amount of time, say 30 seconds. Remove the bucket from the water stream at the end of 30 seconds and measure the amount of water collected using a one gallon container (such as, a milk jug). For example if you collect 3 gallons in 30 seconds equals 6 gallons per minute times 60 minutes per hour equals 360 gallons per hour. Your water supply in this example is 360 GPH. Keep in mind that the amount you calculate should likely be considered the maximum amount so that when planning the number of zones that can be run from this one source to allow for 75%- 80% of maximum flow. Another factor to consider in setting up a drip irrigation zone is that only a given amount of water can flow through a certain pipe size at a set pressure. The most common size drip tubing of ½ inch can support a flow of 220 gallons per hour at 25 PSI. This means that if you have a 25 PSI pressure regulator for the drip emitters and are using 1 GPH emitters there can be no more than 220 emitters on this one system. If using ½ GPH emitters there could be up to 440 emitters on one system. There are also limits on the length of polytubing that can be run on any one drip zone and still maintain the desired pressure of say 25 PSI. As the length of tubing increases there is more resistance in the tubing to push the water through. When that length reaches a certain point the loss in pressure could eventually be noticeable. Layout of a drip zone If plants are of sufficient size so that emitters are needed more than on just two sides of plants, additional emitter(s) can be added to reach another area under the drip line by inserting a ¼ fitting in the drip line, attaching ¼ tubing to this and inserting an emitter at the end of the desired length of tubing. For larger plants where several emitters are needed to adequately cover the root zone, one option is to circle the plant with ½ poly tube and place emitters as needed along the circle. The circle of poly tube can be laid out by inserting a Tee in the drip line and connect the circling tubing to the Tee. In situations where many emitters are needed in the circle, drip tubing with embedded emitters could be used instead of inserting emitters one at a time. When watering annuals, ground covers or plantings that have a solid cover of the soil surface it would be necessary to water a solid area. This can be done by emitter lines with emitters spaced every 12-18 inches and placing parallel emitter lines 12-18 apart for a uniform irrigated area. If watering a solid area, a time and labor saving method of accomplishing this is by using drip tubing with emitters molded into the tubing. Drip tubing with emitters molded into the tubing can be purchased with emitter spacing of 12, 18, 24 or more. The drip tubing is very similar to the solid drip line tubing and has similar handling characteristics. 3
In most situations it will be necessary to run more than one drip line to cover all of the planting area in the drip system. The drip line is flexible enough to allow for slight curves along the route; it does not have to be run perfectly straight. Multiple lines can be routed in whatever spacing and pattern needed and connected by a mainline or manifold line that supplies the water. This is where the various fittings come into play. There are tees, ells and crosses that can be used to fit the layout of the design. In most homeowner situations, drip irrigation tubing is usually installed on top of the soil surface and then covered with mulch. This makes it easy to install, inspect the system and allows much less exposure of the applied water to evaporation losses. It also keeps the tubing and water from being heated too much in the summer sun. Before the lines are covered with mulch be sure to turn on the system to flush any trash out of the system and to easily check the watering pattern. Remember in planning and laying out the watering zones that there is a limit on the amount of water your system can supply and a limit in the total length of line in any one zone. For plantings with straight runs and no curves a very cost effective drip irrigation setup is the use of drip tape. Drip tape is constructed of thinner material so that when there is no water pressure in the line the tubing collapses. Emitters are built into the tubing in a twin wall construction and typically spaced 12-18 apart. Drip tape is especially useful in a vegetable garden in that it can be taken up and put out of the way at the end of the crop season. Installation is very similar to other drip systems in that water can be supplied with ½ poly tubing as a main line. A special fitting is then punched into the tubing, much the same way emitters are installed, and the drip tape is connected to the fitting. These fittings also come with the option of an on/off valve so that an individual row can be turned on or off without effecting water flow in the remainder of the system. The end of the line of drip tape is closed off by folding back the tape making a crimp in the line and securing the crimp with a sleeve of a piece of the drip tape. Micro Irrigation and Drip Emitters, Micro-sprinklers In some circumstances such as ground cover areas, dense plantings or irregular shaped areas drip irrigation may not be the best choice. In many of these situations, microsprinkler or micro-sprays are the better choice for irrigation. Micro-sprinklers have been described as tiny streams of water, usually multiple streams coming from the water delivery device. Micro-sprayers deliver a miniature spray pattern. Micro-sprayers usually have higher flow rates than drip emitters and wet a larger area in a circular, part circle or fan shaped pattern. They operate under the same low pressure as emitters and connect to the water distribution tubing in the same manner. Micro-sprinklers may have a spinning disc which distributes the water. The force of water coming out of the spray nozzle striking the disc causes the disc to spin and distribute the water in a pattern over the irrigated area usually in a full circle. Microsprayers typically do not have any moving parts and have the usual small particle spray pattern. Micro-sprinklers and micro-sprayers come in a variety of coverage areas 4
patterns ranging from 5 to possibly up to 45. They may be mounted on spikes to reach above the canopy of the covered plants or even as a pop-up from level with the plant canopy. Micro-sprinklers are also useful for irrigating larger plants, such as large shrubs or trees, where using drippers alone would require a large number of emitters. The variety of flow rates and spray patterns for micro-sprinklers makes it possible to match the sprinkler to the requirements of the plant and planting area. Some micro-sprinklers have a set pattern while others are adjustable with merely a turn of a dial to change flow rate and area covered. In most situations the larger the area covered will also mean a higher flow rate. The reverse is also true so that the resulting water deposition per square foot is similar whether the area covered is a large diameter or smaller one. This is useful in design considerations where a mixture of sizes of sprinklers can be placed on the same water supply line and amount of time the sprinklers are run does not have to be different. The flow rate of 220 GPH maximum for ½ drip tubing must be remembered so that the number of micro-sprinklers installed flow rates do not exceed this amount. Micro-sprinklers are connected to the water supply line using 1/4 microtubing and are inserted into the microtubing using a threaded connection. The water inlet stem of a micro-sprinkler is threaded instead of the barb stem used for emitters. This threaded stem easily screws into the end of microtubing to securely hold the micro-sprinkler. Screw the sprinkler in until the base of the sprinkler touches the tubing. It is easy to continue turning the sprinkler but this will strip the threads just made in the microtubing and weaken the hold in the tubing. The microtubing end is expanded slightly when the sprinkler is inserted, thus it is important when changing a sprinkler to unscrew it and cut off about the end ½ of the tubing. The new connection will then be screwed into an unexpanded area that has not been stretched. Another point to consider in installing micro-sprinklers in ¼ tubing is that the length of the tubing can not be an indefinite length due to a pressure drop of extended runs. This will likely not be a limitation to using micro-sprinklers. A run of 3-4 ft. from the supply line should be adequate for most installations and will not adversely affect the flow rate to the sprinkler. Components of Drip Irrigation Drip irrigation systems can be simple and fairly easy to install by following a few guidelines in the design and installation. A basic drip irrigation system has the essential components of a water supply source, such as an outdoor faucet, a supply line for the water and the emitters. Other necessary parts of the drip system include a backflow preventer (anti-siphon device), pressure regulator, filter and fittings to connect all the pieces together. Backflow Preventer- is a device that prevents impure water in your irrigation system from being sucked back into your household water supply. When everything is working as it should the water is flowing from your water faucet through the drip system to your thirsty plants, but should there be a loss of water pressure the water may flow backwards. Which means the little pieces of compost, mulch, worm parts and other unpleasant things can flow back down the drip tubing into your clean water. The backflow preventer 5
causes a vacuum break and the back siphoning does not happen. It is screwed directly to the outdoor faucet supplying the drip irrigation system as the first component. Should the drip irrigation setup become so large as to need a water supply other than your outdoor faucet more elaborate backflow prevention will be needed and required by local codes. Be sure to check with local governing agencies or a licensed irrigator in that situation. Pressure Regulator- Most drip irrigation systems operate at pressures of 10-30 PSI while the typical water supply system has an operating pressure of 60 PSI or even higher! Drip irrigation components including the fittings, piping and emitters are not designed to operate at these higher pressures and can break or come apart. Thus the role of a pressure regulator is to reduce the water supply pressure to the much lower operating pressure of your drip system. There are two general types of pressure regulators, non-adjustable and adjustable. Most homeowner drip irrigation systems use the non-adjustable pressure regulators that come pre-set from the factory with the desired outlet pressure. Be sure to check the output pressure setting when you purchase the non-adjustable regulator as they come in various settings. Adjustable pressure regulators are certainly acceptable for homeowner drip irrigation systems but are more expensive and are only needed with larger systems. The pressure regulator can be installed next in line after the backflow preventer OR in some situations after the filter. Filter- The filter screens out very small pieces of stuff that may be in the water. Although the water coming out of your faucet appears to be clean and is safe to drink it may pick up small grains of sand and other small items from the supply lines that could clog drip emitters. The openings of drip emitters are very small by their very nature and accumulations of small particles could plug an emitter and stop the drip of water to your plants. A filter is a good preventive measure. Common drip irrigation filters use a 150 mesh screen, which is adequate in most situations. You may find a finer mesh screen such as 200 mesh and can try it if so desired. The 200 mesh screen may need cleaning more often than a 150 mesh, but if you begin to have problems with emitter plugging a 200 mesh screen filter may help. The better quality filters may be installed before the pressure regulator and will have a maximum pressure rating of 150 PSI or a rating close to that figure. If there is not a maximum pressure listed it is likely meant to be installed after the pressure regulator. The higher pressure rated filters are more expensive, but they may have the advantage of protecting the pressure regulator from small particles that will be trapped by the filter. Supply line/tubing- Polyethylene (PE or Poly) tubing is commonly used for the distribution lines in a drip system, particularly in a homeowner system. Poly tubing is flexible, especially if left in the warm sunshine for a while, is easy to cut and can be connected without glue or clamps. Emitters are installed along this distribution line by punching a hole in the tubing and snapping an emitter in place wherever desired. In this manner emitters can be installed to water only the root zone area of plants and not the open spaces between them. In order to water closely spaced and dense plantings it is often necessary to uniformly apply water to the entire planting area. For such situations drip tubing with emitters molded into the tubing can be used. Emitter tubing commonly has emitters spaced 12 to 18 inches apart, and by placing the lines 12 to 18 inches apart uniform wetting of an area can be achieved. 6
Emitters- So how does the emitter do the job of allowing the water to come out of the water line in large, wetting drops? Different emitters do this in different ways. One type is the long path emitter. The water is routed within the emitter in a long, narrow path. The small diameter and length of the path reduces the water pressure so that the water exits the emitter in a more uniform, slow flow. Long path emitters tend to be larger in size in order to have the length needed to reduce the flow to a desired level. Short path emitters live up to their name and use a shorter and smaller water path than the long path type. The short path emitters do not have as uniform water distribution as some other types, but are less expensive and work better on very low pressure systems, such as gravity flow drip systems fed by rain barrels. Another type that uses other means to slow the flow of water out of the supply line are the tortuous path or turbulent flow emitters. These emitters route the water through a path of turns and obstacles that cause turbulence in the water resulting in a low pressure and slow flow out of the emitter. Diaphragm emitters use a flexible diaphragm in the path of water flow to reduce the pressure and control the flow rate from the emitter. Regardless of the means used to reduce the pressure and water flow, there are two basic types of emitters: pressure compensating (PC) and non-compensating/pressure sensitive. Pressure compensating emitters will deliver the same flow rate to the plants within a given operating range of pressure. The water pressure within the delivery line can fluctuate within this range and not change the amount of water emitted to the plant root zone. Many PC emitters are designed to automatically flush themselves momentarily when first turned on and again at shutdown. This helps in preventing clogging. Pressure compensating emitters also deliver a more constant water flow if there are slight differences in elevation along the drip irrigation water line. Water pressure increases 0.43 PSI for each foot of elevation rise. A change of only a few feet is not significant but should be something to keep in mind as the drip irrigation system is designed. Pressure sensitive emitters deliver a constant flow of water so long as the pressure remains constant. An increase in pressure will result in more water being delivered to the plants just as a decrease in pressure will lower the flow of water emitted. Non-PC emitters do not self flush but many are easily taken apart for cleaning. These emitters work fine in smaller systems where there is no pressure drop along the length of piping and elevation differences are minor. Emitters come in various flow rates. The more common flow rates are 0.50 gallon per hour (GPH), 1 GPH and 2 GPH. The lower flow rates allow more time for the water to infiltrate into the soil and to spread laterally. Installation/Assembly As mentioned earlier, starting at the water source, say an outdoor faucet, the first item to connect in the system is the anti-siphon device backflow preventer. Next items are the filter and pressure regulator. All of these parts screw together, but a word of caution. Not all threads are the same. They are either pipe thread or hose thread. Hose thread is the common garden hose thread and it is always ¾. When purchasing the screw together fittings be sure to check the type thread. If the water source is an outdoor faucet, it will 7
be garden hose thread. From that point on the choice is to stay with HT or use a fitting to convert from HT to pipe thread. Garden hose threads use a washer to get a water tight seal, whereas pipe threads need only enough Teflon tape to cover the threads. Do not use any kind of pipe dope, plumbers putty, etc. Use only Teflon tape for pipe threads only. Hand tightening of components is usually adequate. If a wrench is used, tighten no more than ¼ turn. Now that the water is filtered and pressure reduced to the operating pressure of the drip system next comes the drip tubing. Up until this point everything has screwed together with threads in the fittings. The tubing requires a fitting with threads on one end to connect to the last threaded fitting and one end to hold the tubing. This is accomplished with either a compression fitting end or a hose barb. With a compression fitting the hose is pushed inside the fitting and held in place with a reverse facing bevel ring in the inside edge of the fitting. The hose barb fitting is matched to the hose size and fits sufficiently tight inside the tubing to hold without clamps or may have a locking ring mechanism. Polytubing is flexible, but it gets even more so if it is warm. Before you start laying out the tubing, place it in the sun to get warm and increase flexibility. Polytubing comes in a roll. To lay it out, unroll it. If it is uncoiled by pulling on one end, it will come out with kinks in the tubing. As the tubing is unrolled it will tend to recoil. Use bricks or something heavy to hold it down until you get it in place. As the tubing is put in place U shaped stakes can be placed over the tubing to hold it in place. Once the tubing is in place for a few days it will stay in place much easier with less tendency to twist or move. When cutting the tubing to desired lengths it is best to use a good cutter. This helps to get a nice square end. Inserting fittings is much easier with square cut tubing. A knife will cut the tubing but it may be difficult to get a square end using a knife. Use a cutter of some type, possibly heavy duty scissors or a tool for cutting tubing. Emitters are inserted directly into the tubing. Emitters have a flared or barbed end to hold them in the tubing. A hole just large enough to force the barb through is punched in the tubing. The hole should be the correct size so that it will seal properly and not leak. This is best done with a hole punch designed for the job. Using a nail or a plain punch will likely result in an improper fitting hole and a leaky fit. Buy a punch made for emitter tubing. Push the emitter into the hole until you hear or feel it snap into place. That s all there is to it! In some circumstances more than one emitter is needed to adequately water a plant. An emitter may be needed on the opposite side of where the line is run. In those situations ¼ microtubing can be used to carry water to other locations by inserting a barb fitting into the polytube, insert the other end of the fitting into a length of microtubing and put an emitter on the end of the microtubing. Some emitters may have a stem opposite the barb fitting. In those cases, the emitter can be placed in the polytubing and a length of microtubing run to the desired location, thus not needing an emitter on the end or a need for the fitting to hold the microtubing. Should you need to change the location of an emitter or replace one, try pulling it straight out of the tubing so not to enlarge the hole by moving the emitter back and forth. If the replacement emitter leaks at the tubing then a repair plug called a goofplug is used to 8
plug the hoe. A goofplug has two stems, one larger than the other. First try the smaller stem and test for leaking. If it leaks, then insert the larger stem. The emitter can be reinstalled a couple of inches from the original hole. If you have to replace an emitter inserted in microtubing, work the emitter out by moving back and forth. Once removed cut off about ½ of the tubing end that held the stem of the emitter since the end is likely stretched and will at some time begin to leak. Cutting off the end will get back to like new tubing. Now the emitter tubing is complete except that water will come out of the open end. There are basically two means of closing off the end. One uses a fitting shaped like a figure 8 and looks like two rings attached together. One end of the ring slips over the polytubing far enough to fold the tubing back and the tubing end inserted through the other ring. This crimps the tubing to close it and the figure 8 fitting holds the crimp in place. The figure 8 fitting is very effective and can be removed for opening the line again at any time should it be needed. Another means of closing off the end of the polytubing is by using a fitting which has a screw cap plug. The cap can be removed to allow free flow of water out the emitter tubing. There are numerous manufactures of drip irrigation components and that has caused a little confusion and caution for consumers when it comes to drip tubing. Drip tubing or polytubing is a special piping commonly used in drip systems. Drip tubing is thin wall and has a low pressure rating (typically about 50 PSI). The problem is there are several sizes often referred to as ½ size when actually they are not exactly the same size. As shown in the following table: Size(commonly called) Inner Diameter Outer Diameter Wall Thickness Compression Ring Color ½ 0.500 0.580 0.040 Yellow ½ 0.520 0.620 0.050 Green ½ or 5/8 0.600 0.700 0.050 Black ½ or 5/8 0.620 0.710 0.045 Blue If possible, it is advisable to purchase drip tubing from the same source and to get the same brand in order to likely get the same size. While the sizes are close enough so that there is little difference in water flow, the problem comes in getting the right fittings. A connection may fit firmly in a slightly different size tubing but at some point it will begin to leak or come apart unless securely clamped. It is just easier to match the fittings to the size tubing. Controller It is not as easy to see when drip systems are operating as it is with conventional sprinklers. Thus the system may remain on longer than planned and overwater an area. A useful item for the drip irrigation system is a controller. A very basic controller is a simple timer that turns off after a set time, for example 1 hour, 2 hours, etc. More advanced battery operated timers are available that can be set to day(s) of week to operate 9
and length of time to run. A battery operated controller would be especially useful when away from home for several days to keep the plants watered. There are controllers with garden hose threads that attach directly to the outdoor faucet. These should be installed as the first item at the faucet with the anti-siphon backflow prevention device installed after the controller. Selected References Low Volume Landscape Irrigation Design Manual, Rain Bird Sales, Inc., Landscape Drip Division, 113pp. 2000. Guidelines for Landscape Drip Irrigation Systems, Arizona Landscape Irrigation Guidelines committee, July 2000, www.amwua.org, 58 pp. Installation Instructions, Drip Microsprayer Watering System for Home Landscape Area, The Drip Store, 1145 Linda Vista Dr. Ste. 108, San Marcos, CA 92069, 8 pp., 2005. Drip (Trickle) Irigation Systems, Michael A. Kiser, Oklahoma Cooperative Extension Service, BAE-1511. Principles of Micro Irrigation, Dorota Z. Haman, Forrest T. Izuno, University of Florida, IFAS Extension, AE 70. 2003. Maintaining Drip Irrigation Systems, Gary A. Clark, William J. Lamont Jr., Charles W. Marr, Danny Rogers. Kansas State University, MF-2178, April 1996. Basics of Microirrigation, B-6160, 01-05, Juan Enciso & Dana Porter. Texas Cooperative Extension Service. Retrofitting a Traditional In-Ground Sprinkler Irrigation System for Microirrigation of Landscape Plants, Dorota Z. Haman, Michael D. Dukes and Sydney G. Park-Brown, Univeristy of Florida, IFAS, ABE324, Rev. 8/2004. Irrigation of Lawns and Gardens, Dorota Z. Haman, Gary A. Clark and Allen G. Smajstrala, University of Florida, IFAS, CIR 825, Rev. 10/05. Drip Irrigation Design Guidelines, Jess Stryker, www.irrigationtutorials.com. Web Links DripIrrigation.com Tutorials DripWorksUSA.com Tutorials IrrigationDirect.com Tutorials DripDepot.com Irrigation.tamu.edu Drip Irrigation and Watering Web Links, Compiled 2005-08-08 by Robert A. Schultheis, Natural Resource Engineering Specialist, University of Missouri Extension, Marshfield, MO 65706. 10