Minimum water requirements of four turfgrasses in the transition zone

Water requirements for 'Meyer' zoysiagrass (Zoysia japonica Steud., hereafter re- ferred to as zoysia), 'Midlawn' bermudagrass (Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt-Davy, hereafter referred to as bermuda), 'Falcon II' tall fescue (Festuca arundinacea Schreb.) and 'Brilliant' kentucky bluegrass (Poa pratensis L., hereafter referred to as bluegrass) were evaluated under a mobile rainout shelter at defi cit irrigation levels of 20% to 100% of actual evapotranspiration (ET a ), applied twice weekly, between June and September 2001 and 2002. Soil was a river-deposited silt loam (fi ne, montmorillonitic, mesic Aquic Arquidolls). Minimum annual irrigation amounts required to maintain quality ranged from 244 mm for bermuda to 552 mm for bluegrass. Turfgrass species and respective irrigation levels (% of ET a ) at which season-long acceptable turf quality was maintained in each year were bluegrass, 100% (evaluated 2001 only); tall fescue, 60% in 2001 and 80% in 2002; bermuda, 60% in both years; and zoysia, 80% in both years. A landscape manager who could tolerate one week of less- than-acceptable quality could have irrigated tall fescue at 40% ET a (224 mm) in 2001 and 60% ET a (359 mm) in 2002. Likewise, bermuda exhibited unacceptable quality on only one September rating date when irrigated at 40% ET a (163 mm) in 2001. Bermuda was able to tolerate a lower leaf relative water content (LRWC) and higher level of leaf electrolyte leakage (EL) compared to other grasses before quality declined to an unacceptable level. Turfgrass water use rates often exceed natu- ral precipitation, and during extended periods without rainfall, restrictions may be imposed limiting water that can be applied to turf areas. As such, researchers have sought to identify turf species and cultivars that have good drought resistance (Aronson et al., 1987; Carrow, 1995; Fry and Butler, 1989), and irrigation manage- ment techniques to reduce water inputs. Some grasses, such as bermuda and tall fescue, have deep root systems that help them avoid drought when precipitation is limited (Qian et al., 1996). Others, such as zoysia, have shallower root systems, but tolerate drought using osmotic adjustment and other physiological mechanisms (Qian and Fry, 1997) Over the past 20 years, several researchers have addressed the subject of defi cit irrigation, returning water in amounts less than ET a , as a water conservation technique (Feldhake et al., 1984; Fry and Butler, 1989; Qian and Engelke, 1999). Turf managers overseeing installation of new golf courses, housing developments, and other turf areas are commonly queried by government administrators as to how much ir- rigation water will be required to maintain an acceptable quality turf in the landscape. How- ever, the amount of water required to maintain LRWC and EL of zoysia, bermuda, tall fescue, and bluegrass in the transition zone.