Subsurface Drip Irrigation Guide - Page 5

Everyone knows that the least expensive truck, microwave, house paint, or trencher is not simply the one with the lowest price tag. Rather, the product that ends up costing the least over its useable life is the least expensive.

So too with an irrigation system. Without getting caught up in a bidding war with a competing contractor, the professional who can explain why his system will perform better, over a longer time, and ultimately cost less, has an excellent chance of winning the job.

When you can add both the savings in water and the savings in maintenance to the total system cost, you have a compelling proposition for the buyer.

We already know that a dripperline system is going to save from 30% to 70% of the water of a sprinkler system, and with water cost increases and watering restrictions and bans a reality, that would be enough for most. But here is a study done by a maintenance company in Arizona that compared the maintenance cost of an overhead sprinkler system to a subsurface Netafim dripperline system. It included three apartment buildings with approximately the same amount and type of landscape to maintain. All of the properties were maintained in the same way and by the same company.

The reality of maintenance is this:

• Maintenance of a subsurface dripperline system is dramatically less than a sprinkler system
• Special training is not needed for crews

Specifics regarding system maintenance are covered at the end of this guide.

Note: A contractor in Maryland has told Netafim that he "hates" drip. When asked to explain, he said that he simply cannot generate the same number of repair calls with Netafim that he can with a sprinkler system.

When companies extrude dripperline, they do so using a variety of drippers, flow rates, and styles. Once the dripper and dripper flow rate are chosen, decisions then have to be made on how far apart the drippers will be from each other in the tubing, how thick the walls of the tubing will be and how large the diameter of the tubing will be.

For our purposes, Netafim USA's Landscape & Turf Division only recommends a "heavywall" pressure-compensating dripper in its subsurface-approved products. They include Techline CV and Techline. These pressure compensating dripperlines not only provide the same flow rate all the way along the dripperline, but the drippers also have a continuous self-flushing mechanism that make them more dirt and debris resistant - superior performers. Lastly, they are designed to last as long or longer than any other component in the system.

Netafim Techline CV and Techline Dripperline have a "Continuous Self-Flushing" feature that sets them apart from other products. The operative word is "continuous." Any time debris gets into the dripper, the same diaphragm creates the pressure compensating feature, momentarily shifts position and flushes the debris out of the dripper. After that split-second of purging is complete, the dripper goes back to its normal operation. In comparison, other drippers on the market tout a self-flushing feature but all that means is that at the moment the dripperline turns on, or just after it shuts off, debris may be released. What isn't being said is that during operation, if a dripper becomes clogged, it stays clogged.

Different companies have different flow rates for their drippers. Virtually all drippers used in subsurface landscape applications use a flow rate of less than 1.0 gallon per hour (GPH). Netafim Techline CV and Techline are offered in a broad range of flow rates in order to match the flow rate to the soil's ability to absorb the water.

In deciding the proper dripper to use, it is based primarily on the soil (and slope):

• Sandy soil, use a dripper that emits either 0.6 or 0.9 GPH
• Loam soil, use a 0.4 or 0.6 GPH flow rate
• Tight soils like clay, either a 0.26 or 0.4 GPH flow rate dripper

The Maximum Precipitation Rates Chart from the U.S. Department of Agriculture shows the ability of various soils to absorb water. This information is important because it is the best way to show how different soils manage water. In the case of Coarse Sandy Soil on a 0 to 5% Slope, it can absorb 2.00" of water if covered with vegetation. Conversely, a heavy clay/clay loam soil can only accept about 0.20". This means that sandy soil does not hold water as well as tighter soils. It also means that sandy soil will not radiate the water as far laterally and upward as a tighter soil. As such, care needs to be taken when deciding what dripper flow rate to use and how far apart the drippers can be from each other. And as the slope increases, this takes on even greater importance.

Once the proper dripper flow rate is selected (based on soil and slope), the proper dripper spacing inside the tubing needs to be determined. Netafim uses dripper intervals of either 12" or 18," regardless of dripper flow rate. We also offer a 24" spacing for specialty applications. The last determinate is how far apart the rows will go.

Note: When Netafim's Landscape & Turf Division first began, there were many myths about drip, most of them concerning point source drippers. The most common misconception was that it took hours and hours of irrigation to get the right amount of water applied. With most low volume products at that time being point source drippers, this might have been the case. After all, if too few drippers were used, it would be necessary to run the zone for long periods to deliver enough water. But the advent of dripperline changed that. If you were going to get a contractor's attention, you needed to be able to deliver a lot of water in a short amount of time. That is the reason recommendations from several years ago fo spacings and row spacings that delivered more water than is recommended today.

Figure 26 - Dripperline diameters.

As for the various inside diameter (I.D.) or outside diameter (O.D.) of tubings today, it varies. Unlike most mid sized rotors with a " inlet, or sprays with a " inlet, dripperlines come in a variety of wall thickness and I.D./O.D.

Netafim Techline CV and Techline tubing have a wall that is thicker than most, (0.050") and have a 0.560" I.D. This converts to 17mm (" nominal) and is considered the norm for dripperline. With its thicker wall, it is considered a permanent product, meaning it is designed to last as long or longer than any other component in the system.

Low volume does not mean low application rate or low precipitation rate.

If an average rotor system is applying 0.4 inches per hour, that does not mean it is delivering 0.40" of water usably to the root zone.In fact, it is probably only delivering about half that amount.

Figure 27 - 12" x 12" typical end feed layout.

Conversely, Netafim Techline CV and Techline, using a 0.9 GPH flow rate on a 12" x 12" grid are applying 1.44 inches per hour, and anywhere from 85% to 95% of the water is useable.

If a low application rate is used, it will most likely be in response to the realities of the earlier United States Department of Agriculture Chart linking application rate to type of soil and slope. In this case, using something that puts down more water than the soil can handle is bad water management.

Knowing the soil type is important to picking the proper flow rate for the dripper. It is equally important to know the type of soil because it will drive what dripper interval you use (12" or 18") as well as how far apart you space the rows.

Most contractors can easily determine soil type from these three choices, but what if your professional opinion is that it is clay-loam, or a sandy-loam?

As you review our General Guidelines Chart on page 26 you will see that as the soil selection changes from clay to sand, we move from a lower flow rate dripper to a higher flow rate dripper and our dripper interval and row spacings get closer.

Bottom Line: If you are in doubt between clay and loam, choose loam. If the decision is between loam or sand, choose sand. Why? The rows and dripper intervals will be closer, and yes, the dripper's flow rate could increase as well. The result will be that you have not overextended the spacings. Remember too that the information in Table 4 from the United States Department of Agriculture regarding the soil's ability to absorb water is based on type, cover and slope.

Note: When amending a soil, do not add more than 15% to 20% organic compound to it. Adding too much organic compound can cause the water to be absorbed and reduce the effective wetted area.

Subsurface Drip Irrigation Guide - Page 5