Hunter PRS-40’s with MP rotators used to irrigate all research plots during the course of this study. Photo by Sean McLaughlin
Golf courses spread across the southwestern United States continue to be significantly impacted by extreme and persistent drought conditions. Many state and local governments have recently implemented sweeping emergency ordinances that significantly limit
or prohibit the use of irrigation water for various turf areas in residential and commercial landscapes alike (3).
Restrictive legislative action aimed at reducing water usage is nothing new to superintendents and turfgrass managers in the Southwest. Persistent drought, however, combined with warming temperatures and reduced availability of water across the region,
has brought increasingly difficult challenges for many facilities, and fears of more intense water restrictions are a reality many may soon face. While turf reduction projects in out-of-bounds and rough areas have dramatically reduced water consumption
and have been shown to be one effective solution to reducing golf course water use, more focus can be made on large playable areas of the golf course, like fairways, which make up roughly 30% of total maintained turf area on the average-sized golf
course (2).
Figure 1. Research plots at Cal Poly Pomona University in Southern California were set up to measure soil moisture using three different soil moisture sensor technologies. Diagram by Sean McLaughlin
With the introduction of soil moisture sensor (SMS) technology in popular handheld equipment, a more scientific and precise approach to water management has thus far proven to be an effective tool in greens management. The existing drawback to handheld
SMS devices, however, is the cost in time and labor to check soil moisture throughout the golf course. For these reasons, many golf courses restrict the use of this technology to greens, while larger fairway areas are irrigated based off evapotranspiration
(ET) rates. ET, while calculated using the modified Penman-Monteith equation derived from meteorological data, is still an estimate and not a truly accurate measure of actual water usage for a specific crop and site (1).
When irrigating to replace ET losses, superintendents and water managers are irrigating after water has been transpired by the plant and often after signs of wilt have already begun to develop. SMS technology allows users to actively monitor live water
content in the effective root zone, allowing the user to watch real-time trends in soil moisture, track actual water usage by the plant and irrigate before plant wilting points are reached. Exploring the implementation of this technology in larger
turf areas such as fairways (which would allow a greater reduction potential in water savings) could prove a new method for superintendents to further reduce overall turf irrigation to meet constricting water usage requirements.
To explore this potential, research was conducted to address the performance of hybrid bermudagrass (Cynodon dactylon × C. Transvaalensis) fairways monitored with SMS technologies from The Toro Co. (Turf Guard Soil Monitoring System), Rain Bird
(Integrated Sensor System) and Tucor Inc. (Soil Moisture Monitoring) when compared to traditional evapotranspiration-based irrigation practices. This research was conducted to analyze water savings between SMS- and ET-based irrigation scheduling,
and to determine the ability of each treatment to maintain acceptable turfgrass quality while still reducing water usage.
Table 1. Irrigation schedule based on evapotranspiration readings.
Materials and methods
Research was conducted at the Center for Turf Irrigation and Landscape Technology (CTILT) at Cal Poly Pomona University in southern California from fall 2018 to spring 2020. No data was collected during the winter dormancy season. This field study was
performed on 12 existing 10-foot-by-10-foot (3-meter-by-3-meter) GN-1 hybrid bermudagrass turf plots maintained at fairway conditions. For the purpose of this study, “fairway conditions” were defined as having a mowing height of 0.50 inches
(1.27 centimeters), mowed with a reel mower twice per week and growing in full sun in a native clay-loam soil. Each research plot was independently irrigated and had a designated flow meter to accurately measure applied water on a plot-by-plot basis.
ET-based irrigation (control) and SMS-based irrigation (treatments) plots were assigned on a randomized complete block design with three repetitions of each control and treatment (Figure 1). Moisture sensors were installed to the manufacturer’s
suggested recommended depths for each technology and monitored via SMS software.
Figure 2. Water consumption by date, measuring evapotranspiration as well as three soil moisture sensor technologies.
Data to analyze water consumption of each repetition was collected via flow sensors measuring total water usage for each plot, season to season. Quality, density and color ratings were collected weekly following the National Turfgrass Evaluation Program
rating scale of 1 to 9 (1=poor, 9=excellent, 6=minimally acceptable). Weekly clipping yield measurements were also collected to measure a representative sample of two-day turf growth for each repetition.
ET rates were collected from an on-campus California Irrigation Management Information System station, and readings were adjusted monthly for hybrid bermudagrass growing in the southern California region (4). Control plot irrigation commenced every other
day to replace ET losses for the previous two to three days (Table 1). Treatment (SMS) plots were irrigated when volumetric water content (VWC) readings fell to temporary wilting point (27% VWC) for a clay loam soil and irrigated until field capacity
(36% VWC) was reached (5).
Figure 3. National Turfgrass Evaluation Program turf density rating measured according to evapotranspiration as well as three soil moisture sensor technologies.
Results
Results of this study showed that SMS technology can effectively reduce overall water consumption at golf course fairway settings while still maintaining acceptable hybrid bermudagrass quality under fairway conditions (Figure 2). When soil moisture sensors
were able to maintain gravimetric water content at or above 15%, the resulting turfgrass quality consistently received visual color, quality and density ratings of minimally acceptable levels or above (NTEP score of 6 and above) (Figures 3-5). This
would suggest optimal turfgrass growth under the given irrigation regime when applying water based on SMS readings. It was noted that higher volumetric water content in ET plots did result in slightly better overall turfgrass growth and performance
based on both clipping yields and turfgrass visual ratings. Despite this, treatment plots with lower volumetric water content readings still produced turfgrass quality at or above minimally acceptable levels based upon visual ratings in comparison
to ET plots.
Figure 4. National Turfgrass Evaluation Program turf color rating measured according to evapotranspiration as well as three soil moisture sensor technologies.
During this study, SMS technology was effectively able to reduce overall water consumption by an average of roughly 30% to 50% of ET while still maintaining acceptable turfgrass conditions (Table 2). Overall water savings varied from season to season,
presumably due mainly to changes in seasonal temperatures. As a result, the contrast in water savings between treatments and controls was most substantial in the hot summer season.
The contrast in water savings between ET-based irrigation scheduling and SMS scheduling was far less dramatic during the cooler fall seasons.
Figure 5. National Turfgrass Evaluation Program turf quality rating measured according to evapotranspiration as well as three soil moisture sensor technologies.
Conclusion
The results in this study have shown SMS technology is more effective when it comes to water savings than ET-based irrigation scheduling. SMS technology was most effective in reducing overall water usage during the hot summer months, when water demand
is highest and supply is most often strained. Soil moisture sensor technology may prove a more useful tool for golf course superintendents in the southwestern U.S. in reducing overall water consumption on larger golf course fairway areas while still
maintaining a quality turfgrass stand.
Table 2. Water savings measured according to evapotranspiration as well as three soil moisture sensor technologies.
Funding
This research was funded by the United States Golf Association.
Acknowledgments
Soil moisture sensor hardware/software and irrigation components were donated for the purpose of this research by The Toro Co., Rain Bird and Tucor Inc.
Literature cited
- Allen, R.G., L.S. Pereira, D. Raes and M. Smith. 1998. Food and Agriculture Organization. Crop evapotranspiration — guidelines for computing crop water requirements. Chapter 4 – Determination of ETo. Retrieved Sept. 1, 2022, from https://www.fao.org/3/x0490e/x0490e08.htm.
- GCSAA. Golf Course Environmental Profile. 2016. Retrieved March 1, 2019, from https://www.gcsaa.org/docs/default-source/Environment/phase-2-land-use-survey-full-report.pdf?sfvrsn=c750ea3e_2.
- Jensen, J. 2022. Golf courses in the Southwest starting to feel the pain of historic drought. GCSAA.org. Retrieved Aug. 8, 2022, from https://www.gcsaa.org/resources/regional-resources/southwest/southwest-blog/2022/05/31/golf-courses-in-the-southwest-starting-to-feel-the-pain-of-historic-drought
- Meyer et al. 1985. Irrigation of turfgrass below replacement of evapotranspiration as a means of water conservation: determining crop coefficient of turfgrasses. Pages 357-364. in: F. Lemaire, ed. Proceedings of the fifth International Turfgrass Research
Conference, Avignon, France, July 1985. INRA Publications, Versailles, France.
- Turgeon, A.J. Turfgrass management (ninth edition). Pearson, 2011.
Sean McLaughlin received his M.S. and B.S. in Plant Science with emphasis in Turfgrass Science from Cal Poly Pomona University (Pomona, Calif.). He is currently golf superintendent at the University of Southern California (USC) men's and women's golf facility in Los Angeles.