Evaluation of Turfgrass Species and Varieties for Drought Tolerance along a Linear Gradient Irrigation System.

Given recent EPA watersense criteria and growing municipal restrictions on landscape irrigation, identification of drought tolerant turfgrasses and cultural management strategies for coping with water deficit are more important than ever.  The objectives of this project are to 1) determine for a variety of species and cultivars the minimal irrigation (relative to ET_o) required to achieve desirable turf quality, 2) identify varieties and species exhibiting the greatest drought tolerance and least environmental impact, and 3) identify cultural management strategies that promote optimal water use efficiency.  The study is in its third season on a 2.5 acre site at Texas AgriLife Urban Solutions Center, Dallas, TX.  The four-replicate randomized complete block layout supports 22 turfgrass varieties representing six species.  Plots are managed at two nitrogen levels and two mowing heights.  The irrigation system creates a linear gradient of water availability such that the inner section of each plot receives 120% of ET_o and the outer section receives no supplemental water.  Turfgrass quality, density, canopy and soil temperatures, and soil volumetric water content are being monitored.  Over the initial two seasons, some interesting trends have emerged.  First, the two annual nitrogen rates have not significantly influenced any of the parameters under evaluation.  The buffalograsses consistently exhibit the greatest drought tolerance whereas tall fescue, the lone C3 species has shown the least drought tolerance.  Zoysiagrass, bermudagrass, and St. Augustinegrass species have exhibited relatively similar levels drought tolerance.  To this point, varietal differences within species have been difficult to detect.  Managing turf at higher heights of cut results in improved quality in areas of plots receiving less water; however, Zoysia matrella varieties tend to exhibit an opposite response.  With the exception of buffalograss, which maintains a relatively constant canopy temperature from wet to dry zones, deficit irrigation tends to produce significantly greater heat loads.