Subsurface Drip Irrigation for New Mexico Turf

Southwest Yard & Garden by guest writer 

Dr. Bernd Leinauer, NMSU Extension Turfgrass Specialist

Twitter @NuMex_Turf

Clickable links for related columns on irrigating turf and selecting the right turf for your yard!

This week, the question comes from yours truly (i.e., Dr. Marisa Thompson, regular writer of this column). I’ve heard about subsurface drip as an improved way to irrigate turfgrass, so I invited NMSU Extension Turfgrass Specialist Dr. Bernd Leinauer to bring us up to speed:

Figure 1. Bermudagrass plots irrigated for 6 months with 70% less water than deemed necessary for perfect grass. Subsurface drip irrigated bermudagrass is shown on the left and sprinkler irrigated bermudagrass on the right. (Photo courtesy of Matteo Serena.)

Subsurface Drip Irrigation for Lawns

Despite their proven inefficiencies, pop-up sprinklers are still the most common systems for irrigating lawns or other turf areas. Sprinkler overspray, overlap, wind drift, and evaporation losses all contribute to water losses that increase overall water consumption and/or decrease plant quality. An alternative to sprinklers is subsurface drip irrigation (SDI). Drip irrigation systems have been frequently used to irrigate trees, shrubs, flower beds, or vegetables, but they’ve received little acceptance for turfgrass irrigation. They offer a solution for lawns that are difficult to irrigate, such as narrow strips, slopes, or unusual, irregular-shaped areas, which is the case for many residential lawns.

SDI systems irrigate either from a point (equally spaced emitters) or a line source (e.g., soaker hoses) using polyethylene pipes buried at shallow depths. SDI’s benefits have been extensively studied in agriculture, but SDI has received very little acceptance or attention for turf irrigation, despite strong evidence of its water savings.

Advantages and Disadvantages

Advantages of SDI compared to sprinklers include energy savings due to a lower operating pressure, no human exposure to irrigation water, reduced plant disease pressure, and water savings. Water savings of 50 to 90% have been reported when turf was irrigated using SDI (Figure 1). With SDI, water is applied directly in the rootzone only to the area requiring water (Figure 2). Savings result from improved distribution uniformity (no sprinkler overlap), no water loss due to wind drift, and no evaporation losses during irrigation. Another advantage is that turf areas can be used during irrigation, which is important for golf courses or athletic fields.

Arguments against SDI include higher installation costs and difficulty in determining spacing and depth of pipes or emitters. Other arguments against SDI are based on inaccurate assumptions, including a perceived inability to establish SDI irrigated turf from seed or sod, a perceived interference with regular maintenance, and a perceived inability of SDI irrigated rootzones to leach salts.

Figure 2. Cross section of bermudagrass rootzone with drip line 3 inches below the surface.

 Cost

Potential additional costs of SDI depend on a number of issues, and therefore will vary from substantially more to less than sprinkler systems. Costs for material and installation (labor) depend on the soil type, size, and shape of the irrigated area. Areas that require many connections to the header lines can be significantly more expensive than a sprinkler system for the same area. However, SDI systems used on areas that require only a few connections to header lines (e.g., long and relatively narrow areas of turf) can be less expensive than sprinklers (Figure 3).

Figure 3. Subsurface drip irrigation systems work well for narrow areas that may be more difficult to irrigate using traditional sprinklers. Drip lines placed on surface covering a long, relatively narrow area (left). Turfgrass area after drip lines were covered with soil and sod (right).

Interference with Turfgrass Maintenance

Research has shown that SDI-irrigated turf can be fertilized with granular fertilizer without any loss in color or quality. If sufficient soil water is present, nutrients from the granule will become plant-available regardless of whether water is applied from the surface or subsurface. However, most large turf areas with an SDI system have an injection system and apply liquid fertilizer. Home lawns can also be fertilized with a hose-end sprayer (foliar/liquid fertilization tool). If granular pesticide applications require watering-in from the surface, either hand watering or a temporary surface irrigation system may have to be used. Core aeration can be applied if the drip lines are installed below the penetration depth of the core aerator. Deep tine aeration cannot be conducted on SDI-irrigated turf.

Life Expectancy

We have no published data available on the longevity of SDI systems. We recommend that all SDI systems be installed with filters (disk, screen, or sand) (Figure 4) and flush valves to prevent clogging from sediments/particles. Potential root intrusion can be addressed by using products (e.g., Toro DL2000®, Netafim TECHLINE® HCVXR, or Rainbird XFS) that offer technology that protects the emitter from root intrusion. Our oldest SDI system was installed in 2003 and is still working fine (Figure 5).

Figure 4. Two irrigation valves with screen filters (center) to supply water to SDI system.

Figure 5. Backyard bermudagrass lawn 12 years after installing the SDI system.

Installation

SDI systems in lawns should be installed 3 to 6 inches below the surface. It is easiest to install if the pipe network can be placed directly on the ground and subsequently covered with soil up to the appropriate depth. However, an SDI system can also be trenched into soil that is already in place (Figure 6) or trenched into an existing lawn (Figure 7).

Figure 6. Trenching into top soil (left, center). Trench with drip line following the shape of the turfgrass area (center). Tall fescue lawn one year after SDI was installed (right).

 Figure 7. Trenches cut into dormant bermudagrass lawn.

The drip line depth and emitter spacing depend on the type of soil, type of grass, and whether or not there is a slope. Our general recommendation is to place emitters and drip lines 1 foot apart (Figure 8), particularly in sandy soils. However, for finer-textured soil, such as silt or clay, emitters can be spaced up to 18 inches apart. On slopes, lines should be placed closer together at the top but farther apart at the bottom to account for internal downhill water flow. If SDI is used close to driveways, walkways, or other hardscape, place emitters no more than 6 inches away from these surfaces to avoid dry soil along that border.

Fig 8. Surface wetting pattern from drip lines placed 3 inches deep and emitters spaced on a 1-foot grid.   

Drip lines are usually connected to header lines, also called manifolds (Figures 9, 10). Commonly used SDI lines are 0.5 inches in diameter, but manifolds should be larger and can be anywhere from 0.75 to 2 inches, depending on the length of each drip line and the lawn’s size. Larger manifolds should be used on each end of the drip line and allow for sufficient water supply at the appropriate pressure to each drip emitter. If areas are small and drip lines are relatively short, manifolds can be made of drip lines (Figure 11).

Figure 9. Manifold made from a 1-inch diameter solid PVC pipe. 

Figure 10. Manifold made from a flexible 0.75-inch diameter pipe following the contours of the turfgrass area. Drip lines are connected to header line using a PVC tee and an adapter. 

Figure 11. Manifold made of drip line. (Photo courtesy of Matteo Serena.) 

Guest author Dr. Bernd Leinauer (NMSU Extension Turfgrass Specialist, @NuMex_Turf) is based in Las Cruces and performs research in turfgrass water conservation. Regular author Dr. Marisa Thompson (NMSU Extension Urban Horticulture Specialist) is based at the NMSU Agricultural Science Center at Los Lunas.

For more gardening information, including decades of archived Southwest Yard & Garden columns, visit the NMSU Extension Horticulture page (http://desertblooms.nmsu.edu/), follow us on social media (@NMDesertBlooms), or contact your County Extension office (https://aces.nmsu.edu/county).