Golf Course Management

SEP 2013

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research Top: Salinity buildup is evident in the cool-season turfgrass plots during February 2006. Bottom: Cool-season grasses that were irrigated with potable water from a sprinkler system. The photo was taken in April 2006. 88 GCM September 2013 three-year research period appears to be the result of inadequate heat tolerance and is not necessarily due to salt stress. Tall fescue provided the highest quality among the cool-season grasses in our study. These fndings support those of other researchers (8,10), who rated tall fescue either moderately tolerant or tolerant to salinity. Superior salinity tolerance of tall fescue compared to other cool-season grasses may be the result of salinity avoidance, which is achieved by developing a deep root system that remains viable at depths below those at which salt accumulates. Although rooting depth was not measured in our study, other authors (9,13) have reported that tall fescue is able to avoid drought through its deep and extensive root system. Others have observed a high root/shoot ratio in salt-stressed tall fescue (2). In our study, tall fescue quality received an average rating of either 6 or 7 when irrigated with saline or moderately saline water (Table 3). Similar turf quality was observed for inland saltgrasses A138 and DT16 and bermudagrasses NuMex Sahara and Transcontinental, both of which are generally considered more salt-tolerant than cool-season tall fescue (15). However, more research is necessary to determine whether quality of tall fescue grown in a saline environment can remain as high as that of salt-tolerant warm-season grasses on a long-term basis. Visual quality ratings of Brightstar SLT, Catalina and Dawson support other research (4,8) that ranked salinity tolerance of perennial ryegrass as similar to that of slender creeping red fescue cultivars. In our study, perennial ryegrasses Brightstar SLT and Catalina only maintained acceptable quality under irrigation with potable water (Table 3). Irrigation with moderately saline and saline water resulted in turf quality below an acceptable minimum of 6. In our study, the quality of Dawson under saline irrigation was higher than that of both perennial ryegrass cultivars. As in alkaligrasses, the low quality we observed in both perennial ryegrasses and creeping red fescue may have been due to high summer temperatures and not salinity stress. This would explain why quality ratings for these three grasses never exceeded 6, even under potable irrigation (Table 3). Other studies have also found perennial ryegrass and creeping red fescue to be heat-sensitive species (6,11). Moreover, no recovery was observed for Catalina plots after summer 2006 or for Dawson and Brightstar after winter 2006, despite lower salinity levels in the root zone compared to previous years (Table 3, Figure 1). Simultaneous heat and salt stress may have been detrimental to both species, resulting in little or no recovery. In contrast, tall fescue successfully recovered to acceptable quality levels at the end of the research period. Investigating the relationship between salinity and turf quality revealed that more than one stressor affected visual quality of cool-season grasses in our study. Despite a wide range of salinities measured over the three-year research period, quality could only be signifcantly predicted from soil salinity for four cultivars. Furthermore, only 18% and 27% of the variations in quality can be explained by soil salinity. Further research in cooler climate zones is needed to investigate the role of temperature and salinity on turf quality of cool-season grasses. Visual quality of turfgrasses was not affected by the type of irrigation when potable water was used. Other research (7) reported a signifcant reduction in quality of Kentucky bluegrass, perennial ryegrass and tall fescue under drip irrigation as opposed to sprinkler irrigation. However, our results agree with recent research in New Mexico (14,15) that reported no decline in turf quality of subsurface-irrigated cool-season grasses during a four-year research period and no difference in quality between sprinkler and drip-irrigated plots of several warm-season cultivars. In our study, cool-season turfgrass plots irrigated with saline water from a sprinkler system exhibited higher quality than plots irrigated from the drip systems in spring and summer 2006. The higher turf quality of sprinkler-irrigated plots may be due to lower EC and sodium content at rootzone depths of 0-4 inches (Figures 2, 3) compared to drip-irrigated plots. During summer and fall 2007, grasses that received drip irrigation with moderately saline water exhibited lower quality than grasses that were sprinkler-irrigated. By the end of the research period, the turf quality of both sprinkler- and drip-irrigated plots receiving moderately saline or saline water was below the acceptable minimum rating of 6, suggesting that cool-season grasses generally do not perform well when irrigated with more-saline water on a longterm basis in a transitional desert climate. The high correlation between percent ground cover and quality suggests that reduced turf quality is mainly due to a lack of green cover. However, loss of green cover may not necessarily be attributed to a complete loss of plants, as several other researchers (8,12,16) have reported leaf fring and loss of pigmentation during the early stages of salinity and heat stress in cool-season turfgrasses. Conclusions Our results indicate that most of the cool-

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