The application of subsurface drip irrigation (SDI) on turfgrass requires placing drip emitters and driplines in close proximity to provide a continuous wetted pattern throughout the turfgrass growing area. Field trials conducted at the Center for Irrigation Technology (CIT) since 1989 indicate healthy turfgrass can be grown using the SDI system. A total of 12 products were evaluated in the test plots. These products included hard hose, drip tapes, and porous tubing.
Of the products tested, some showed signs of root intrusion within 60 days. Others, like the porous tubing, showed no signs of root intrusion, but distribution uniformity declines were noted after several years of operation due to the buildup of fine particles in the water passages. These particles are smaller than 200 mesh, but larger than the water passages (Solomon and Jorgensen 1992).
From the original 12 products which began the SDI evaluation, only two continue to maintain the appearance of problem-free, high-quality turfgrass. In the spring of 1994, nine emitters from each of these two products were excavated to evaluate root intrusion. One product showed two of nine emitters to have roots penetrating the labyrinth, affecting the discharge rate. The second product showed no signs of root intrusion in any of emission pathways. This second product incorporates an herbicide into the plastic which is continuing to provide protection from roots after five years of service.
The drip tubing for the SDI test plot evaluations was installed prior to sod installation at a depth of four inches (net depth with turf was ± 5 in.). Distance between the lines ranged from 10 to 24 inches. Irrigation scheduling was designed to replace 150 percent of actual crop ET. The application of 50 percent more than actual crop ET represents the non-uniformity found in many sprinkler irrigation systems.