How well various warm-season grasses perform during drought conditions and their water requirements to maintain acceptable turf quality are important questions that this study sought to answer. Photo courtesy of Mingying Xiang
Editor's note: This article is reprinted from the Aug. 18, 2023, issue of the USGA Green Section Record. Copyright United States Golf Assocation. All rights reserved.
Significant progress has been made in breeding warm-season turfgrasses for improved characteristics, such as drought tolerance, winter color, cold tolerance and texture. Despite improvements in drought tolerance achieved through several USGA-funded turfgrass
breeding programs, there is limited information on the relative irrigation requirements of many cultivars of bermudagrass, zoysiagrass and buffalograss released over the past several decades. Additionally, many golf courses — particularly in
the Southwest, where water resources are costly and/or limited — have posed the question of whether zoysiagrass or new cultivars of bermudagrass are a better alternative to older cultivars due to a perceived reduction in water use. Turf managers
would benefit from better information on the water-use requirements of warm-season turf when deciding on a specific cultivar or species. To address this issue, a joint USGA and National Turfgrass Evaluation Program warm-season water-use trial was
initiated. Data was collected for three years at eight sites across the U.S., with the study being completed in 2022. The results from this study give turf managers insight into the water requirements for specific cultivars of warm-season turf at
a wide range of locations and climates.
The trial had two unique objectives and methodologies. Approach 1 estimated the amount of water the grasses needed to maintain acceptable quality by irrigating individual plots under a rainout shelter. Approach 2 evaluated the performance and survivability
of the grasses under practical and reduced irrigation levels by irrigating plots using three different evapotranspiration-replacement regimes.
Eleven cultivars of bermudagrass, four cultivars of zoysiagrass and two cultivars of buffalograss were evaluated. The trials were maintained in a consistent manner across locations, following standard growing recommendations for the region. Each study
was established in the local soil type, with no sand capping and no sand topdressing applied. Plots were maintained at 0.5 inch (1.27 centimeters), a typical golf course fairway mowing height, and other stresses were minimized.
Table 1. Location, study approach, Köppen climate type and study length in days for a joint USGA-National Turfgrass Evaluation Program water-use trial.
Study Approach 1: Individually irrigated turf plots under a rainout shelter
Materials and methods
Four locations were chosen to conduct the rainout shelter study: Jay, Fla.; Griffin, Ga.; Starkville, Miss.; and Stillwater, Okla. During the first year, plots 3 feet by 3 feet (0.91 meter by 0.91 meter) were established from seeds or plugs (seeded cultivars
noted in Table 2). At the beginning of the summer in years two, three and four of the study, turfgrass plots received a uniform amount of irrigation; thereafter, water replacement was suspended, and data collection began.
During the acute drought imposition, turfgrasses were evaluated regularly (either daily, biweekly or weekly) according to the irrigation needs in each region. When the turfgrass quality of a specific cultivar was below acceptable, estimated when the plot
reached a level of 65% wilt coverage determined by digital image analysis, the turf was hand-watered with a volume of water necessary to return the plot to an acceptable percent wilt and turf quality level. Each plot that required hand-watering and
the amount applied was then recorded. The dry-down period lasted from 21 to 113 days (Table 1), after which normal irrigation resumed and recovery was measured.
Table 2. Species, cultivars and inches of irrigation required per day to maintain acceptable turf quality during varying lengths of simulated drought under a rainout shelter in 2021. Each value is an average of three replicates. Blue shading denotes low water use, red denotes high water use and white denotes moderate water use.
Key results
The results for each cultivar in the trial were averaged over the four study locations and are presented in Table 2 as inches of water needed daily to maintain acceptable turf quality. Notable results are summarized below:
- Bermudagrass cultivars TifTuf and Tahoma 31 were consistently the top-performing cultivars and required the least irrigation water to maintain acceptable turf quality.
- Among zoysiagrass cultivars, the experimental variety FAES 1306 required the least amount of water. The older cultivar Meyer had the highest water requirement of all cultivars.
- The buffalograss cultivars Cody and Prestige generally performed in a range between the other two species.
- The highest water requirement came from bermudagrass cultivars PremierPRO and Dog Tuff.
- In Florida, five bermudagrass cultivars and one zoysiagrass cultivar did not require irrigation, and in Oklahoma, three bermudagrass cultivars did not require irrigation. We could attribute this to plant genetic improvement, local environmental conditions
and soil type.
- In Mississippi, zoysiagrass required more than twice the amount of irrigation compared to most of the bermudagrass and buffalograss cultivars.
Study Approach 2: Three levels of ET-based irrigation
Materials and methods
Approach 2 required a larger area than Approach 1, with three ET-based irrigation levels scheduled in separate sections. Each section of turf was either hand-watered, or a sprinkler system was installed to provide one of three levels of irrigation. Each
study was set up with three replications for each ET level. The locations reporting data were Riverside, Calif.; Las Cruces, N.M.; College Station, Texas; and Fort Lauderdale, Fla. Buffalograss did not survive the climatic conditions at the Fort Lauderdale
location as indicated with blank cells in Table 3.
The first year was used to establish the turf. Years two through four were used to impose the chronic drought treatments. Each plot at each site had irrigation set at one of three levels: 60% replacement of ET (considered an adequate amount of water for
warm-season turf), 45% replacement of ET or 30% replacement of ET. Depending on the location, irrigation was applied one or three times per week for between 121 and 148 days. In case of a rain event, irrigation was withheld, and the amount of precipitation
was subtracted from the next irrigation event.
Table 3. Turfgrass quality by location on a scale of 1-9, where 1=poor turf quality, ≥6=acceptable turf quality, and 9=perfect turf quality. Red shaded cells denote low quality; yellow cells denote acceptable turf quality; and green denotes best quality. Note: Buffalograss did not survive in Florida.
Key results
Results for each trial location are shown in Table 3 as average turfgrass quality rated on a 1 to 9 scale — with 1 being poor, 6 or above being acceptable and 9 being perfect – for each cultivar under the three irrigation regimes. With significant
environmental variability, turfgrasses performed differently at each location, hence the importance of trials in many regions across the U.S. Below are summaries of the results by cultivar and location:
- Averaged over locations and ET levels, TifTuf bermudagrass was the best-performing cultivar of any grass, maintaining an average quality of 6.5 under the 30% ET irrigation regime. Tifway (6.0 quality) and Tahoma 31 (5.8 quality) were the second-
and third-best cultivars at that irrigation level.
- No buffalograss or zoysiagrass cultivars maintained acceptable quality under the 30% ET irrigation regime when averaged across locations (excluding Florida). The best two zoysiagrass cultivars were CitraZoy and Stellar, with an average quality of
5.5.
- No cultivar of any species maintained acceptable quality at the 30% ET regime in Riverside, but TifTuf had acceptable quality (6.2 quality) at the 45% ET-replacement irrigation regime.
- In the high desert environment of Las Cruces, TifTuf, Tahoma 31 and Tifway maintained acceptable quality at the 30% ET regime. Further, all zoysiagrass cultivars had acceptable quality at all ET-regime levels. Buffalograss was among the worst performers,
even at the 60% ET regime, most likely due to factors including the fairway maintenance regimen, less-than-ideal climate and prolonged drought.
- In College Station, trends were similar among the top-performing zoysiagrass and bermudagrass cultivars as in other locations. However, the two buffalograss cultivars Prestige and Cody had above-acceptable turf quality across all irrigation regimes,
even at 30% ET replacement. Considering all trial locations, Central Texas may have been best suited for buffalograss maintained at fairway height.
- In Fort Lauderdale, turf quality was acceptable for nearly all irrigation regimes and cultivars, and differences among cultivars were minimal, despite the study being run in its driest season.
Conclusion
This study demonstrates that there are important differences in water requirements among warm-season grasses — both old and new — depending on the species, cultivar and location for use. Turf managers planning to establish warm-season grasses
at their course where water use is a consideration should establish a trial of multiple options a few years before renovation to see how different species and cultivars perform at that specific site under that specific planned maintenance program.
For superintendents wondering whether zoysiagrass or new bermudagrass cultivars perform better in drought conditions, this study suggests that the answer depends on location. Although buffalograss only produced acceptable turfgrass quality in College
Station, it’s worth noting that trial conditions were not conducive to maintaining buffalograss at fairway height, whereas previous research has shown it can produce high-quality fairways given the right conditions (1).
The research says
- Warm-season grasses are often mentioned for their drought tolerance and ability to help courses save water, but there are significant differences in the water requirements among species and cultivars.
- In this study, bermudagrass generally exhibited higher drought tolerance than zoysiagrass or buffalograss, and newer cultivars such as TifTuf and Tahoma 31 showed improved drought resistance compared to older bermudagrass cultivars such as Tifway.
- Meyer zoysiagrass required more water than improved zoysiagrass varieties to maintain acceptable turf quality in simulated drought conditions, and newer zoysiagrass cultivars had higher turf quality ratings under a typical irrigation regime, i.e.,
60% replacement of evapotranspiration.
- Buffalograss had similar water requirements as the other two species to provide acceptable turf quality under a rainout shelter, but buffalograss quality declined more rapidly than zoysiagrass or bermudagrass under the same ET-replacement level in
the field. This limitation was likely due to the variability in climate of each site and relatively short mowing height.
- The response of turfgrass species to drought varied depending on the local climate and cultivar. Prior to selecting a grass, it’s essential for golf courses to establish test plots to evaluate species and cultivars for multiple seasons in their
unique growing environment and under their desired irrigation regime.
Acknowledgement
The USGA and NTEP thank all the turfgrass research scientists and their supporting teams who conducted trials at several locations over multiple years. Comprehensive data from all study locations and years for this trial are available from NTEP (https://www.ntep.org).
Literature cited
1. Frank, K.W., R.E. Gaussoin, T.P. Riordan, R.C. Shearman, J.D. Fry, E.D. Miltner and P.G. Johnson. 2004. Nitrogen rate and mowing height effects on turf-type buffalograss. Crop Science 44(5):1615-1621 (https://doi.org/10.2135/cropsci2004.1615).
Matteo Serena, Ph.D., (mserena@usga.org) is the senior manager of irrigation research and services for the USGA Green Section; Kevin Morris is president and executive director, National Turfgrass Evaluation Program; and John Petrovsky, CGCS, is manager
of Green Section Education.