Irrigate--don't ignore--fairway trees

On many golf courses, fairway trees are forgotten where irrigation is concerned. However, the notion that "the sprinklers will give them enough water" is not always true. To flourish, trees not only need more water than what they get from turf irrigation, they also need deeper watering. Drip or other micro-irrigation systems are ideal for providing the water trees need.

Types of irrigation Several methods are available to supply additional water to fairway trees. Because golf courses come in many shapes and sizes, you won't find just one answer to watering trees. On desert-style courses, most or all of the trees are outside of the turf areas. Their water must come from an irrigation system. For golf courses with "wall-to-wall" turf, supplementing the sprinklers' water with deep soaking is the goal. Different conditions require different types of installation and hardware.

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The most popular method of supplying water to trees on a golf course is drip irrigation. Sometimes called "trickle irrigation," this type of system uses emitters to allow water to slowly penetrate the root zone around the tree. Drip systems run for several hours at a time to saturate trees' root zones. You then allow the soil to dry for several days before applying another dose of water.

One popular strategy today is fertilizing trees through the drip-irrigation system. Known as "fertigation," this method of applying nutrients to turf and trees uses at least one injection pump and one or more tanks of liquid fertilizer. A series of hoses, tubes and controls regulates the flow of nutrients into the water stream at the desired proportion.

A second method of irrigating trees is the bubbler system. Bubblers are similar to drip emitters, except that they discharge water much faster. Rather than trickling slowly for hours, bubblers can fill a tree well in a matter of minutes. The water then gradually soaks into the root zone for deep watering.

Micro-irrigation is the term often used for the entire family of slow-irrigation products because of the small amount of water they supply. Besides drip emitters and bubblers, you can use micro-sprays to saturate a larger root-zone area. Used mostly in agriculture, these devices require relatively high maintenance when located in turf areas.

Flood irrigation sometimes is used in certain areas for deep watering of trees and is still one of the best methods for doing so. For example, many of the older golf courses in Arizona contain "flood basins" in the rough areas where trees may receive this flood-type water. One advantage is that it is cheap water. However, disadvantages include: * Flood irrigation water is not available in most locations * The water covers areas much larger than the root zones of individual trees and therefore is wasteful * Weeds and turf pathogens travel with the flood irrigation water.

At least one manufacturer (Tree Gator) supplies plastic "bags" that you fill with water. Small perforations allow measured amounts of water to slowly seep into the soil. By placing these units around trunks of small or newly planted trees, you efficiently can supply them with water. Although this is not a long-term solution for tree irrigation, it can help new transplants become established in the absence of a fixed irrigation system.

A range of products * Drip emitters. Emitters are constructed of black acetyl plastic. They are black to reflect the ultra-violet rays of the sun. Emitters have small openings for slow watering and contain diaphragms to help provide a consistent delivery rate. They are durable and heat-resistant, and liquid fertilizers and herbicides do not affect them.

Drip emitters come in several varieties. They can be either 0.5-inch threaded (for PVC pipe) or barbed (for polyethylene). They range from 0.6 to 3 gallons per hour (gph) in water delivery per outlet, the most common types being 1 and 2 gph. Manufacturers provide single-outlet or multi-outlet models-the multi-outlet version is usually better for trees. Emitters also are either pressure-compensating or non-pressure-compensating. The pressure range to the emitters should be 15 to 35 psi for the non-compensating type. We recommend non-compensating types because, in our experience, these emitters don't clog as easily due to their larger passageways for the water. Always use a pressure regulator with each drip valve on your golf course, even when using the pressure-compensating type. We also recommend using wye strainers.

* Bubblers. Named for their pattern of water discharge, bubblers are a good choice if you already have "wells" around your fairway trees. If you don't have wells, it is difficult to contain the water. Bubbler rates are adjustable and discharge between 1 and 5 gallons per minute in most cases. Bubblers typically fill single tree wells with water in 5 to 10 minutes. Bubblers consist of black plastic material and include a filter screen and stainless-steel adjusting screw. They are available in a 0.5-inch threaded configuration and in a pop-up body if you don't want the bubbler sticking up above ground.

* Microsprays. These devices are made of black plastic material with different nozzle colors to distinguish various nozzle sizes. They spray a fine mist onto the ground surrounding the tree, supplying additional water to a relatively large zone. Microsprays generally discharge 10 to 15 gph, so you don't need to run them as long as emitters. Their major drawback is that they remain above ground, so it may be difficult to avoid them during maintenance practices. Therefore, we don't recommend microsprays for golf courses.

Installation techniques * Emitters' successful use depends on proper installation. On golf courses, use threaded emitters on PVC pipe to stand up to the maintenance typical of such sites. You can use barb-type emitters on polyethylene tubing, but you can't operate as many on a valve as with PVC laterals because the flow characteristics of polyethylene are not as good. They also don't hold up as well under traffic and heavy maintenance equipment.

Always use adjustable pressure regulators and wye strainers with emitter installations (see photo, page G 12). The pressure in golf-course irrigation systems usually is in the range of 90 to 135 psi, but emitters operate best at 20 psi. Use non-clog, diaphragm-type, non-pressure-compensating emitters and a valve with a regulator and strainer about every 600 feet. Set the regulator at about 25 psi unless you have elevation rises of more than 10 feet (then set it higher).

Pipe-installation techniques vary according to whether you have a new or existing golf course. For new installations, trenching the pipe is usually the best method. Depending on the soil type, however, "pulling" the pipe with a vibratory plow often is acceptable. For existing golf courses, definitely pull the pipe with a plow. This allows a neat, clean installation with a narrow slit in the turf, which heals in just a couple of weeks. Typically, most of the pipe can be 0.5 inch, with some 0.75-inch and 1-inch pipe near the 1-inch electric valve. You only need to dig holes where you'll make the main-line connections to valves and where you site the emitters around the trees. At the emitters, run 0.25-inch "spaghetti" tubing from the emitter outlets around the tree to at least three and as many as six locations at least 18 inches from the trunk (see figure, page G 10). Place this tubing just below the surface so only the tip of the tube is exposed. You'll be able to see the water drip out of the end of the tube when you turn on the valve.

* Bubblers. Install bubblers in much the same way as drip emitters-on rigid PVC pipe with risers (see figure, bottom of page G 10). Because they discharge more water than emitters, you'll need to use larger valves (probably up to 2 inches) and pipe sizes. Graduate the line, starting with 2-inch pipe near the valve, down to 0.5-inch for the last bubblers on each line (use PVC-pipe standards). If possible, we recommend installing each bubbler in a 2-inch PVC sleeve filled with pea gravel for protection.

Maintenance requirements Just as with anything else on your golf course, emitter or bubbler systems require some maintenance. Periodically turn them on to watch their operation and replace or repair any damaged units or piping. Be sure to clean out the wye strainers every 3 months or so and check the discharge pressure on the regulator gauge. Place pea gravel under valve boxes for drainage and to protect the boxes from sinking.

Fairway trees on golf courses need adequate water to provide the lush look and shade that golfers expect. Whether you choose drip or bubbler irrigation, you can be assured that the trees will make good use of the water and respond with healthy growth.

Allen George is an irrigation consultant with Coates Irrigation Consultants (Scottsdale, Ariz).

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