Evaluation of Depth and Spacing of Subsurface Drip Irrigation Emitters for Turfgrass Irrigation in a Silt Loam Soil.

Increased pressure on potable water supplies is creating demand for water conservation practices such as water harvesting and utilization of more efficient irrigation methods like subsurface drip irrigation (SDI). However, little research exists regarding the proper depth and spacing of SDI emitters for turfgrass. The objectives of this study were to determine proper depth and spacing of SDI emitters and examine the feasibility of using harvested rainwater for turfgrass irrigation in Wisconsin.  Irrigation lateral and emitter spacing of 30, 45 and 60 cm at depths of 13 and 25 cm were examined; treatments are hereafter identified by spacing/depth notation. Soil moisture, turfgrass quality and color index were evaluated weekly. Soil moisture measurements were taken every 20 cm on grids measuring 122 by 122 cm. Eight-four percent of rainfall was collected from summer rain events and used for irrigation on a Kentucky bluegrass (Poa pratensis L.) lawn on a silt loam soil. Estimated ET exceeded precipitation by 7.1 cm for a 4-week period in August/September resulting in drought symptoms developing in some plots. Significant differences in turfgrass quality among treatments were detected on four of nine evaluation dates.  Treatments of 45/13 cm and 45/25 cm had the greatest turf quality throughout the study, while treatments 30/13 cm and no irrigation had the lowest. Color differences among the treatments were only detected on one rating date. Mean soil moisture content for the season was greatest for treatment 45/13, significantly greater than the un-irrigated control and the treatments with spacing 60 cm. Variation in moisture content across the grid for irrigated treatments was not statistically greater than the variation of the un-irrigated control. For this soil type, in 2008, drip emitter spaced at 45 and 13 cm depth provided acceptable turf color, quality and uniform soil moisture at the surface throughout the season.