One means of achieving water conservation in turf management is by providing water at rates below a plant’s maximal consumptive water use, otherwise known as deficit irrigation (Feldhake et al., 1984; Fry and Butler, 1989; Qian and Engelke, 1999). Relative to their cool-season counterparts, warm-season turfgrasses are well adapted for deficit irrigation practices, largely due to their superior water-use efficiency and tolerance of heat and drought (Brown and Kopec, 2000; Fu et al., 2004).
Bermudagrass (Cynodon ssp.) is a widely used warm-season turfgrass species that has shown the capacity to maintain acceptable appearance at deficit irrigation levels (Fu et al., 2004; Wherley et al., 2014). However, little is known concerning how irrigation water quality may affect the extent of deficit irrigation tolerable by turfgrass. This has become an increasingly important consideration, especially in light of the growing number of maintained turf sites using nonpotable or low-quality irrigation sources. Throssell et al. (2009) reported that 24% of golf facilities in the southeastern United States and 37% of facilities in the southwestern United States irrigated with recycled (effluent or reclaimed) water. Facilities within these two regions also reported the most irrigated acres per facility of all seven U.S. regions surveyed.
Nonpotable water sources often contain high levels of sodium that may cause plant-related problems, soil related problems, or both. For example, saline water sources often contain high levels of sodium chloride causing direct osmotic injury to turf shoots, roots, or both. Salinity stress ultimately renders the plant unable to absorb water present in the soil (Marcum, 2006; McFarland et al., 2002). Another common problem associated with low-quality irrigation water is the presence of sodium bicarbonate, which can cause rapid deterioration of soil structure due to dispersion of soil colloids (Marcum, 2006). Golf courses in regions of the United States with greater dependence on recycled water also noted that sodium-related water quality issues including elevated sodium absorption ratios (SAR) and sodium carbonates were primary concerns with their water (Throssell et al., 2009). Asano et al. (1984) reported on effluent water-quality parameters for multiple wastewater treatment plants in California and noted that Na content of the sources generally ranged from 109 to 186 ppm and SAR ranged from 3.3 to 5.7. Information concerning direct effects of sodic irrigation water on turfgrass growth and water use is lacking.
As water availability for turfgrass irrigation becomes more limited, it is also of practical interest to explore products capable of reducing water consumption and/or improving turfgrass quality under drought stress. Plant growth regulators such as TE [4-(cyclopropyl-a-hydroxymethylene)-3,5-dioxo-cyclohexanecarboxylic acid, ethyl ester] reduce turfgrass shoot growth by inhibiting the biologically active forms of gibberellins (King et al., 1997; Turgeon, 2002). Application of TE has been reported to improve heat and drought tolerance of cool-season turf species perennial ryegrass (Lolium perenne L.) and creeping bentgrass (Agrostis stolonifera L.) (Jiang and Fry, 1998; McCann and Huang, 2007). However, in the previously mentioned study with bentgrass, TE was applied several weeks before the onset of drought conditions. Since, turfgrasses generally metabolize TE within 2 to 6 weeks (Kreuser and Soldat, 2011), the benefits of applying TE to enhance tolerance to water stress could potentially be improved through repeat applications made both before and during progressive water stress. Information is lacking concerning the effects of TE on tolerance of warm-season turfgrasses to deficit irrigation and drought conditions.
The objectives of this 10-week greenhouse study were to 1) characterize growth, quality, and ET of ‘Tifway’ bermudagrass (Cynodon dactylon × C. transvaalensis Burt Davy) when irrigated at full (1.0 × ETa) or deficit (0.3 × ETa) irrigation levels using three irrigation water sources (RO, sodic, and saline) and 2) determine whether application of TE could mitigate turfgrass quality decline under deficit irrigation.
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