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Yuhung Lin and Yaling Qian

Golf courses in the western United States increasingly are being irrigated with recycled water. Research was conducted on eight golf courses in a semiarid region, including three courses with recycled water irrigation for 10 years, three courses with recycled water irrigation for 18 to 26 years, and two courses with surface water for irrigation for 15 and 18 years. Turf quality of kentucky bluegrass (Poa pratensis) (KBG), the most widely used turfgrass species in the United States, was evaluated on 25 roughs from the aforementioned golf courses. Concurrently, KBG shoot samples and soil samples from these sites were collected. Shoots of KBG were analyzed for mineral concentrations, including sodium (Na), calcium (Ca), magnesium (Mg), potassium (K), chlorine (Cl), boron (B), sulfur (S), phosphorus (P), manganese, iron, zinc, copper, and molybdenum. Electrical conductivity (EC) and sodium absorption ratio (SAR) of soil saturated paste were determined. Recycled water irrigation for 10 and >18 years increased clipping Na by 4.3 and 9.9 times and Cl by 1.5 and 1.3 times, respectively. Compared with surface water irrigation, B concentration in KBG shoots increased by 3.5 times and K concentration reduced by 16% on sites with recycled water irrigation for >18 years. Multiple regression analysis was conducted to identify the relationships between mineral concentration in shoots and turf quality. There was a negative linear relationship between turf quality and Na concentration in the shoots (R 2 = 0.65). Soil SAR in 0 to 20 cm depth was highly associated with KBG shoot Na, as documented by a logarithmic regression of R 2 = 0.70. Stepwise regression indicated that Na accumulation in the shoots was the leading plant variable causing the decline of turf quality under recycled water irrigation. Therefore, it is reasonable to believe that water treatment and management practices that can reduce soil SAR and Na concentration in KBG shoots would improve turf quality and plant health.

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Yaling Qian and Jack D. Fry

Greenhouse studies were conducted on three warm-season turfgrasses, `Midlawn' bermudagrass [Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt-Davy], `Prairie' buffalograss [Buchloe dactyloides (Nutt.) Engelm.], and `Meyer' zoysiagrass (Zoysia japonica Steud.), and a cool-season turfgrass, `Mustang' tall fescue (Festuca arundinacea Schreb.) to determine 1) water relations and drought tolerance characteristics by subjecting container-grown grasses to drought and 2) potential relationships between osmotic adjustment (OA) and turf recovery after severe drought. Tall fescue was clipped at 6.3 cm once weekly, whereas warm-season grasses were clipped at 4.5 cm twice weekly. The threshold volumetric soil water content (SWC) at which a sharp decline in leaf water potential (ψL) occurred was higher for tall fescue than for warm-season grasses. Buffalograss exhibited the lowest and tall fescue exhibited the highest reduction in leaf pressure potential (ψP) per unit decline in ψL during dry down. Ranking of grasses for magnitude of OA was buffalograss (0.84 MPa) = zoysiagrass (0.77 MPa) > bermudagrass (0.60 MPa) > tall fescue (0.34 MPa). Grass coverage 2 weeks after irrigation was resumed was correlated positively with magnitude of OA (r = 0.66, P < 0.05).

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Hrvoje Rukavina, Harrison Hughes and Yaling Qian

Efforts are ongoing at Colorado State University to develop turf-type saltgrass cultivars. Prior freezing studies have indicated variation in freezing tolerance in saltgrass lines. Therefore, this study was made to examine relative freezing tolerance of 27 saltgrass clones as related to collection sites in three zones of cold hardiness. Furthermore, these lines were evaluated for fall color retention with the intent to determine if there is a correlation with fall color and freezing tolerance. Saltgrass rhizomes were sampled in mid-winter 2004 from lines established in Fort Collins, Colo., and then subjected to a laboratory-freezing test. Saltgrass freezing tolerance was highly influenced by climate zones of clones' origin (P < 0.01) and genotypes within zones (P < 0.01). There was a high negative correlation between color retention in the fall and freezing tolerance (P < 0.01). Average freezing tolerance of saltgrass clones within zones of origin significantly differed among zones. Ranking of zones for least square mean LT50 (OC) was: zone 4 (–17.2) < zone 5 (-14.4) < zone 6 (–11.1). LT50 values in zone 4 ranged from –17.8 (accession 72) to –17.0 (accession 87). Clones in zone 5 showed LT50 values from –17.8 (accession A29) to –11.9 (accession A137). Zone 6 clones had LT50 values that ranged from –9.5 (accession C92) to –12.6 (accession C12). Large intraspecific variation in freezing tolerance may be effectively used in new cold hardy cultivar development. Environmental adaptation inherited by origin of clone is useful in defining clones' adaptation range and may along with fall color retention serve as a selection criterion in saltgrass cold hardiness improvement.

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Hrvoje Rukavina, Harrison G. Hughes and Yaling Qian

Freezing is the major abiotic stress that limits geographic distribution of warm season turfgrasses. Prior studies have indicated variation in freezing tolerance in saltgrass clones. Therefore, this study examined freezing tolerance of 27 saltgrass clones as related to collection sites in three zones of cold hardiness. Furthermore, these clones were evaluated for time of leaf browning in the fall with the intent to determine if there was a correlation between this trait and freezing tolerance. Rhizomes were sampled during 2004 and 2005 midwinters from clones established in Fort Collins, Colo., and then subjected to a freezing test in a programmable freezer. Saltgrass freezing tolerance was highly influenced by the climatic zone of clone origin in both years of the experiment. Clones with greater freezing tolerance turned brown earlier in fall in both seasons. Ranking of zones for the average LT50 (lethal temperature at which 50% of rhizomes died) was: zone 4, most northern (−17.2 °C) < zone 5 (−14.4 °C), < zone 6, most southern (−11.1 °C) in 2004, and zone 4 (−18.3 °C), < zone 5 (−15.7 °C) < zone 6 (−13.1 °C) in 2005. Clones from northern areas tolerated lower freezing temperatures overall. This likely indicates that freezing tolerance is inherited. Large intraspecific variation in freezing tolerance may be effectively used in developing cold hardy cultivars.

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Hrvoje Rukavina, Harrison Hughes and Yaling Qian

Freezing is the major abiotic stress that limits geographical distribution of warm-season turfgrasses. Prior studies have indicated variation in freezing tolerance in saltgrass clones. Therefore, this 2-year study examined the freezing tolerance of 27 saltgrass clones as related to collection sites in three zones of cold hardiness. Furthermore, these clones were evaluated for time of leaf browning in the fall with the intent to determine if there was a correlation between this trait and freezing tolerance. Rhizomes were sampled during 2004 and 2005 midwinters from clones established in Fort Collins, Colo., and then subjected to a freezing test. Saltgrass freezing tolerance was highly influenced by the climatic zone of clone origin in both years of the experiment. Clones with greater freezing tolerance turned brown earlier in fall in both seasons. Ranking of zones for the average LT50 was: zone 4 (–17.2 °C) < zone 5 (–14.4 °C) < zone 6 (–11.1 °C) in 2004 and zone 4 (–18.3 °C) < zone 5 (–15.7 °C) < zone 6 (–13.1 °C) in 2005. Clones from northern areas tolerated lower freezing temperatures better overall. This confirmed that freezing tolerance is inherited. Large intraspecific variation in freezing tolerance may be effectively used in developing cold-hardy cultivars.