A Primer
A quick sleeve across the forehead and break time was over. The engine changed pitch as he thrust the blade at the tall grass. Hadn't he just mowed this five days ago, he thought? Maybe someone had turned the clock up, he pondered, thinking the lawn needed it for the hotter weather. Be a good excuse for a break, go check the clock, fire up the sprinklers...? Like a recoil start, his stomach pinched in a knot as he killed the mower. Where are the sprinkler heads? With seasoned steps his boots probed for the edging sprays. Nothing. Nowhere. Just valve boxes. Was this a joke? Had he taken on a contract with no sprinklers? The auto dealership manager said there was drip irrigation. Surely, he couldn't have meant ...
As Ferreira discovered, and as some of you will in the next few years, more turf areas are being installed with subsurface drip irrigation (SDl) systems. And probably, just like Ferreira did, you will reason that if it made it to this point there can't be much more involved in running it than traditional spray systems.
Ferreira simply looked at the controller settings. He saw that the program was very similar to the other sprinklered lawns he serviced. Maybe a couple more start times, but the duration at 8 to 20 minutes seemed familiar. He started his own educational process through studying the plans and asking questions.
I never met Ferreira until after a year had passed. I wanted it that way. I wanted to know if the landscape maintenance personnel in our area were really ready for a SDI lawn. Having me breathe down his neck would have invalidated the test. I could keep track of the project without interference. He didn't call me until he wanted to know about the fertilizer injector. Just as it should be.
I did not invent SDI in lawns, or for that matter SDI for any area or application. My mentors have spoken of drip being used in lawns in Israel, possibly as far back as 25 to 30 years ago and to this day. I did, however, begin to bury drippers and dripper lines in 1980 (in public contracts). At last count, we have designed and seen installed more than 205 SDl systems. We designed seven SDI lawn systems last year. They are currently being installed.
At first, we only did twin-row burials on each side of perimeter shrub plantings. Seeing the distribution pattern, we realized that at 2-foot dripper and tubing spacing with 1-gallon emitters we could get very quick coverage between the lines. This led us to try a wide variety of spacings with all sorts of plant material.
At the same time, our continuing-education process coupled with a growing movement to native and low-water-use plantings began to coalesce. We found, for example, that roots cannot grow through dry soil or sense the presence of water from a distance. This reinforced our philosophy of irrigating the total potential rootzone, not just the plant.
When we examined our early "full-coverage" SDI grid systems, we also recognized that all we were doing was miniaturizing a typical spray system, only with underground bubblers. Therefore, we decided that within any potential rootzone we should always make it rain.
We did this by flowing sufficient water to evenly soak the soil, just as nature and any self-respecting overhead irrigator would do. From that point on we have never approached SDI systems design much differently from conventional irrigation design. All of the same engineering principles apply.
The greatest difference between overhead systems and SDI is the respect given to the following of contours. SDI systems are, after all, flood bubbler systems. As such, the free water applied (above or below grade) will always flow in a downhill direction first, then laterally because of capillary action. Never overlook this fact.
Around the mid-1980s, buoyed by our ability to successfully grow even moss with SDI, we began to gain experience with turf in controlled situations on our own lawns and lawns of friends. We began conservatively with small areas, then with larger areas as our experience base grew. By 1989, we began offering the alternative of SDI to our commercial customers. The first two designs were for a small entry lawn to a shopping center and a large perimeter lawn for a new car dealership, both installed in 1990. The largest project was a 5.5-acre hydraulically seeded lawn for a school playfield.
We don't do a high volume of SDI turf, perhaps one-third to one-half of the turf areas we are involved with. We don't push it on people. We think that sooner or later everyone will realize there really isn't any difference between a healthy stand of gazania or pittosporurn and 'Alta' fescue turf That realization might come when people figure out fixing anything in a lawn is easier than in a shrub or groundcover bed. This is because of complete unrestricted access coupled with the ability to see potential problems sooner.
We aren't the only ones who have done turf. There are a few others around the country. You hear the stories - soccer field here, baseball diamond there. Don Teal, a landscape architect in Las Vegas, NV, has had considerable experience with SDI in turf. Medals on his SDI turf war chest include a putting green and a regulation tennis court. Some have even designed systems under protest. Everyone seems to have an opinion as to the suitability of subsurface drip irrigation, especially in lawns. What are some of the cons we hear of concerning SDI in turf?
These may or may not be real problems more than perceptions. Even if they are valid issues, a balanced approach has to include a look at some of what we hear are pros concerning SDl in turf.
I could go on, with both pros and cons. Suffice it to say that none of the cons have succeeded in keeping me or others from designing good SDI turf systems.
This is not to say that SDI systems don't have problems. It means, rather, that those problems are not that earthshaking. Here is a handful of what are probably the greatest obstacles one might be faced with while maintaining an SDl turf system:
Wet or Dry Spots: Look first for breaks in either the dripperline or distribution/ collection manifolds. Obviously, any problems here can result in either of the maladies.
Look next at the overall or lateral set (or zone) operating pressure, taken at the flush end(s). If this is low, look to your supply source, particularly at your primary screen filter, then at your primary pressure regulator. If you are still batting "O-fer" and the area(s) are relatively small, you could have plugged emitter(s) or emitter lines that are either too close or too far from the surface.
Emitters that are too deep create the same situation as having an undersized spray nozzle within a system. Being too close to the surface creates the opposite effect. That area will get much more water, just like having an oversized nozzle on a system.
lf you're still hanging out there, you have to consider that the system may have been underdesigned, incapable of exceeding the soil's infiltration rate. This will allow and encourage deep percolation watering (something most lawns scorn with approximately 9O percent of their root mass in the first 12 inches). It does not enable you to rehydrate the upper soil surface, however, until that surface has reached a hydrated condition again.
Primary causes of this condition are insufficient application rates or excessive infiltration rates. We generally use application rates at two to three times the infiltration rate. (Blasphemy, considering we can theoretically match the infiltration rate with these systems). If overall flooding is the problem, cut the water times or shorten them and add start times.
Lines or Stripes in the Turf: Does your lawn look like that odoriferous road kill you passed on the way to work. Well, don't jump into the next county yet; it may not be what you think. Lines will show up on top of emitter lines whenever there is water stress. If this is the case (you have to dig a little), see above. The area's extent should clue you as to where to start. If the lines are between the emitter lines (either lighter or greener than the surrounding area), then you are simply leaching out your nutrients.
It is a well-known phenomenon that salts (including fertilizer salts) will concentrate at the outer edge or "front" of the water movement. In this case, the front is trapped between two lines. Continued watering might eventually dilute the unused material; however, the resulting look of the turf will be less than attractive. The best method of fertilizing is by use of water-soluble, time-release materials injected directly through the system. If you are unlucky and don't/ can't have an injector, you can try broadcasting a high-quality urea based, time-release fertilizer.
Wait... isn't this guy talking about a no-spray system? Yes, I am. If it is in the fall or winter months, you should have sufficient precipitation to carry the material to the soil. If it is not the rainy season, do not despair. Spread your material, then use some type of mechanical method to "brush" the lawn. Rake it. Drag steel or wood bars or try dragging chain-link fencing across the area. All you need to do is start the journey to the thatch area. Remember, the system should create free water on the surface (two to three times the infiltration rate). Capillary action will finish the job of reaching up and pulling it down. Before you run to the chem house, determine what your soil's fertilizer needs are.
Slopes: Not necessarily an irrigator's best friend, sloped areas can present some problems. Depending on the angle (gradient) and length (run distance), two major problems arise. The tops always seem to dry out first. The bottoms are always flooded or pumping water.
This is caused by several factors: The top has no surrounding lawn to protect it from the wind or boost its water reserves, the middle gets the top's excess water, the bottom gets the middle's runoff water as well as its own. This water is not only surface but subsurface as well. Consider the drip "onion." Gravity holds it level at all times; it does not tip perpendicular to the slope. Therefore, the side of the onion on the outside of the slope rarely gets a chance to move below grade; rather, it runs off. All excess is collected at the bottom (just like life).
The solution is to control the movement downhill by controlling the volume applied in a given interval. On really short slopes, you can do this by eliminating (or crimping) emitter lines, starting at the bottom and working up. If your spacing is regular, you might find that crimping the second and fifth lines of a 10-line set is sufficient (Be very careful of pre-spreading the spacing of lines in anticipation of your final spacing; to gain a second chance could be more trouble than it's worth.) Crimping lines enables you to correct your corrections. On longer slopes, you could rezone the set. The top, middle and bottom zones should be on separate valves (just like overhead). This will allow for finite control through run times. Both solutions must incorporate the use of controller "pulsing" of the valves.
Another cause of drain down is the water left in the dripper line flowing downhill to the lower lines. This is very similar to low-head drainage. It should be handled the same way by use of check valves on the distribution manifold risers.
Watering Schedules: This also seems to give everyone a lot of problems. "To wet/ dry or to wet/ wet" is the question on everyone's mind. I think wet/ wet is probably the best method in most instances, especially turf. Wet/ wet is a poor description of simply keeping the soil at a constant moisture level by giving it "sips" of water. Wet/ dry tends to stress the grass more and opens the specter of hydrophobia, something we can all do without. To practice wet/ dry with impunity you must have a very conservative system, say four to six times the infiltration rate.
How much, when? l don't (won't) use plant-specific water-need data. l'm not growing plums. l'm keeping the turf moist. The best way is to use local evapotranspiration data. Again, just like an overhead system. Your application and infiltration rates and slopes will constitute your run-time decisions. By the way, use the regular precipitation-rate formula for your calculations and simply divide the GPM by 60 to allow for gallons per hour instead of minutes. All else is the same. Remember to "recharge" your lower horizon levels occasionally with a deep soak when you are being driven by ETo.
So, how do you decide to use SDl in turf? Sometimes the decision is based on what the customer needs or wants. These could be:
You need to look at the suitability of the site. Will it be a complex system with many small or very special areas? Is the soil more or less uniform in depth or compaction? Do the grades change in rapid succession in the same potentially zoned area?
Look at the cost differential and initial installation as well as long-term maintenance. Understand the difference between the cost of a well-designed overhead system (1O mph wind or better) and an SDl system.
Look closely at your client. Will he lose interest? Can he motivate his maintenance organization? What is his or her "comfort zone"?
Look closely at yourself. What is the level of your expertise and experience? Are good advice, direct help or both available to you? Can you handle any potential liabilities? Have I scared you enough?
I think that any designer or seasoned practitioner can design, install and run a good subsurface drip irrigation system. Careful planning and good advice (manufacturers) are a must. If all else fails, hire a good consultant to help you chart the waters, so to speak.
This article is from Landscape & Irrigation Magazine; March 1995
