This week, the question does come from you (Dr. Marisa Thompson, a frequent visitor to this column). I heard that underground drip irrigation is an improved method of irrigating turfgrass, so I invited Dr. Bernd Leinauer, an expert on turfgrass extension at NMSU, to let us know the latest situation. View photos of subsurface irrigation at https://nmsudesertblooms.blogspot.com/2020/08/subsurface-drip-irrigation-for-new.html

Despite proven inefficiency, pop-up sprinklers are still the most common system for irrigating lawns or other turf areas. Overspraying, overlap, wind drift, and evaporation loss from sprinklers can all cause water loss, thereby increasing overall water consumption and/or reducing plant quality. An alternative to sprinklers is subsurface drip irrigation (SDI). Drip irrigation systems are often used to irrigate trees, shrubs, flower beds, or vegetables, but they are rarely used for lawn irrigation. They provide a solution for lawns that are difficult to irrigate, such as narrow bands, slopes, or unusually irregularly shaped areas, as is the case with many residential lawns.

The SDI system uses polyethylene pipes buried at a shallow depth to irrigate from a point (equal distance transmitter) or a line source (for example, a soaking hose). The benefits of SDI have been extensively studied in agriculture, but SDI has rarely been accepted or focused on lawn irrigation, although there is ample evidence that it saves water.

Compared with sprinklers, the advantages of SDI include energy saving due to lower operating pressure, no human contact with irrigation water, reduced plant disease pressure and water saving. According to reports, using SDI to irrigate lawns can save 50% to 90% of water. With SDI, water is only applied directly in the root zone to areas that need water. The savings stem from improved distribution uniformity (no sprinkler overlap), water loss due to windless drift, and evaporation loss during irrigation. Another advantage is that the turf area can be used during irrigation, which is important for golf courses or sports fields.

The arguments against SDI include higher installation costs and difficulty in determining the spacing and depth of pipes or drains. Other arguments against SDI are based on inaccurate assumptions, including the belief that SDI irrigated turf cannot be established from seeds or turf, that it interferes with regular maintenance, and that the SDI irrigated root zone cannot extract salt.

The potential additional cost of SDI depends on many issues, so it may be greatly increased or decreased compared to sprinkler systems. The cost of materials and installation (labor) depends on the type, size and shape of the soil in the irrigation area. Areas that require multiple connections to header lines can be much more expensive than sprinkler systems in the same area. However, SDI systems used in areas that only need a small amount of connection to the header line (for example, long and relatively narrow turf areas) may be cheaper than sprinklers

Studies have shown that SDI-irrigated turf can be fertilized with granular fertilizer without losing color or quality. If there is enough soil moisture, whether water is applied from the surface or the ground, the nutrients in the particles will become available to plants. However, most large lawn areas with SDI systems have an injection system and liquid fertilizers. Home lawns can also be fertilized with a hose end sprayer (foliar/liquid fertilizing tool). If the application of granular pesticides requires watering from the surface, manual watering or temporary surface irrigation systems may have to be used. If the drip tube is installed below the penetration depth of the core aerator, core aeration can be applied. Deep tooth aeration cannot be performed on SDI irrigated turf.

We have no published data on the lifetime of SDI systems. We recommend that all SDI systems be equipped with filters (disks, screens or sand) and flush valves to prevent clogging by sediments/particles. Products that provide technology to protect the transmitter from root invasion (such as Toro DL2000, Netafim TECHLINE HCVXR, or Rainbird XFS) can be used to solve potential root invasion problems. Our oldest SDI system was installed in 2003 and is still working well.

The SDI system in the lawn should be installed 3 to 6 inches below the ground. If the pipe network can be placed directly on the ground and then covered with soil to an appropriate depth, it is the easiest to install. However, the SDI system can also be dug into the soil already in place or into the existing lawn

The depth of the drip line and the distance between the drippers depend on the type of soil, the type of grass, and whether there is a slope. Our general recommendation is to place the transmitter and drip tube 1 foot apart, especially in sandy soil. However, for fine-textured soils, such as silt or clay, the emitters can be spaced up to 18 inches apart. On slopes, the lines should be placed closer at the top and farther at the bottom to account for internal downhill currents. If using SDI near driveways, sidewalks, or other hard landscapes, place the transmitter no more than 6 inches from these surfaces to avoid drying the soil along the boundary.

The drip line is usually connected to a header line, also called a manifold. The commonly used SDI wire is 0.5 inches in diameter, but the manifold should be larger, which can be 0.75 to 2 inches, depending on the length of each drip line and the size of the lawn. Larger manifolds should be used at each end of the drip irrigation pipeline and allow sufficient water to be supplied to each drip irrigation head at the appropriate pressure. If the area is small and the drip tube is relatively short, the drip tube can be used to make a manifold.

For more gardening information, including columns on Southwest courtyards and gardens archived over decades, please visit the NMSU Gardening Promotion page (http://desertblooms.nmsu.edu/), follow us on social media (@NMDesertBlooms), or contact Your county extension office (https://aces.nmsu.edu/county).

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

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