Conserving water in hybrid bermudagrass stands using soil moisture sensors

Conserving water in hybrid bermudagrass stands using soil moisture sensors


Hunter PRS-40 devices equipped with MP rotors were used to irrigate all research plots during the period of this study. Photography by Sean McLaughlin


Golf courses across the southwestern United States continue to be significantly impacted by severe and persistent drought conditions. Many state and local governments have recently implemented comprehensive emergency ordinances that significantly limit or prohibit the use of irrigation water on various turf areas in both residential and commercial landscapes (3).

Restrictive legislative measures aimed at reducing water use are nothing new for superintendents and turf managers in the Southwest. However, the ongoing drought, coupled with rising temperatures and reduced water availability across the region, has brought increasingly difficult challenges for many facilities, and fears of more severe water restrictions are a reality that many may soon face. While turf reduction projects in rough and out-of-bounds areas have significantly reduced water consumption and proven to be an effective solution to reducing water use on golf courses, more focus can be placed on the large playable areas of the golf course, such as fairways, Which constitutes approximately 30% of the total turf area maintained on an average-sized golf course (2).


Figure 1. Research plots were established at Cal Poly Pomona in Southern California to measure soil moisture using three different soil moisture sensing technologies. Sketch by Sean McLaughlin


Figure 1 Diagram of research plots

With the introduction of soil moisture sensing (SMS) technology into common portable equipment, the most scientific and precise approach to water management to date has proven to be an effective tool in landscape management. However, the current drawback of portable SMS devices is the cost in time and effort of checking soil moisture throughout the golf course. For these reasons, many golf courses limit the use of this technology to greens, while irrigating larger fairway areas based on evapotranspiration (ET) rates. Although ET is calculated using a modified Penman-Monteith equation derived from meteorological data, it is still an estimate and not a truly accurate measure of actual water use for a given crop and location (1).

When irrigating to compensate for ET losses, supervisors and water managers irrigate after the water has filtered from the plant and often after signs of wilting have already appeared. SMS technology allows users to effectively monitor live water content in the effective root zone, allowing the user to view real-time trends in soil moisture, track actual water use by the plant and irrigate before plant wilting points are reached. Exploring the implementation of this technology in larger turf areas such as driveways (which would allow for the potential for greater reduction in water savings) could prove a new way for superintendents to further reduce overall turf irrigation to meet limited water use requirements.

To explore this possibility, research was conducted to address the performance of hybrid bermudagrass (Cynodon dactylon × C. transvaalensis) monitored using Toro Co.'s SMS technologies. (Turf Guard soil monitoring system), Rain Bird (integrated sensor system) and Tucor. Inc. (soil moisture monitoring) when compared to traditional irrigation practices based on evapotranspiration. 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 turf quality while still reducing water use.

Table 1 Irrigation schedule
Table 1. Watering schedule based on evaporation readings.


Materials and methods

The research was conducted at the Center for Turf Irrigation and Landscape Technology (CTILT) at Cal Poly Pomona in Southern California from fall 2018 to spring 2020. No data was collected during the winter dormancy season. This field study was conducted on 12 10 ft x 10 ft (3 m x 3 m) GN-1 hybrid grass plots maintained under corridor conditions. For the purpose of this study, “lane conditions” were defined as having a mowing height of 0.50 in. (1.27 cm), mowed with a reel mower twice a week, and grown in full sun in native clay soil. Each research plot was irrigated independently and had a dedicated flow meter to accurately measure the water applied on a plot-by-plot basis. ET-based irrigation (control) and SMS-based irrigation (treatments) were plots allocated to a randomized complete block design with three replications for each control and treatment (Figure 1). Humidity sensors were installed at depths recommended by the manufacturer of each technology and monitored via SMS software.

Figure 2 Water consumption
Figure 2. Water consumption by date, evaporation measurement in addition to three soil moisture sensing technologies.


Data for each replicate's water consumption analysis was collected by flow sensors that measure total water use for each plot, from season to season. Quality, density, and color ratings were collected weekly according to the National Turfgrass Evaluation Program grading scale from 1 to 9 (1 = poor, 9 = excellent, 6 = minimum acceptable). Weekly cutting productivity measurements were also collected to measure a representative sample of 2-day grass growth for each replicate.

ET rates were collected from a campus irrigation management information system station in California, and readings were adjusted monthly for hybrid bermudagrass growing in the Southern California region (4). Irrigation of the control plot was initiated every 2 days to compensate for ET losses over the previous 2–3 days (Table 1). Treatment plots (SMS) were irrigated when volumetric water content (VWC) readings fell to the temporary wilting point (27% VWC) for clay loam soils and irrigated until field capacity (36% VWC) was reached (5).

Figure 3: Grass density
Figure 3. The National Lawn Assessment Program's turf density rating is measured according to evaporation and transpiration as well as three soil moisture sensing technologies.


results

The results of this study demonstrated that SMS technology can effectively reduce overall water consumption in golf course fairway settings while maintaining acceptable hybrid bermuda grass quality under fairway conditions (Figure 2). When soil moisture sensors were able to maintain gravimetric water content at 15% or greater, the resulting turf quality consistently received visible color, quality, and density ratings of acceptable minimum levels or higher (NTEP score of 6 and above) (Figures 3-5). This may indicate optimal grass growth under the specific irrigation regime when using water based on SMS readings. It was observed that higher volumetric water content in ET plots resulted in slightly better growth and performance of turfgrass overall based on both plot yields and visual evaluations of the turf. However, treated plots with lower volumetric water content readings still produced turf quality at or above minimally acceptable levels based on visual ratings compared to ET plots.

Figure 4: Grass color classification
Figure 4. The National Lawn Assessment Program's turf color rating was measured according to evaporation and transpiration as well as three soil moisture sensing technologies.


During this study, SMS technology was effectively able to reduce overall water consumption by an average of approximately 30% to 50% of ET while maintaining acceptable turf conditions (Table 2). Overall water savings vary from season to season, presumably due mainly to seasonal temperature changes. As a result, the variation in water provision between treatments and controls was greater in the hot summer season.

The discrepancy in water savings between ET-based irrigation scheduling and SMS scheduling was much less dramatic during the cooler fall seasons.

Figure 5: Grass quality rating
Figure 5. The National Lawn Assessment Program's turf quality is measured according to evaporation and transpiration as well as three soil moisture sensing technologies.


Conclusion

The results in this study showed that SMS technology is more effective when it comes to water saving compared to ET-based irrigation scheduling. SMS technology has been most effective in reducing overall water use during the hot summer months, when water demand is highest and supply is often strained. Soil moisture sensing technology may be a more useful tool for golf course superintendents in the southwestern United States in reducing overall water consumption in larger fairway areas of golf courses while maintaining turf quality.

Table 2 Water saving
Table 2. Water savings are measured according to evaporation and transpiration as well as three soil moisture sensing technologies.


Finance

This research was funded by the United States Golf Association.


Thanks and appreciation

The soil moisture sensor hardware/software and irrigation components were donated for the purpose of this research by Toro Co. Rain Bird and Tucor Inc.


Literature cited

  1. Allen, R. G., L. S. Pereira, D. Rice and M. Smith. 1998. Food and Agriculture Organization. Evaporation and transpiration in crops – Guidelines for calculating crop water requirements. Chapter 4 – Determining ETo. Retrieved September 1, 2022, from https://www.fao.org/3/x0490e/x0490e08.htm.
  2. GCSAA. Environmental profile of the golf course. 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.
  3. Jensen, J. 2022. Golf courses in the Southwest begin to feel the pain of historic drought. GCSAA.org. Retrieved August 8, 2022, from https://www.gcsaa.org/resources/regional-resources/southwest/southwest-blog/2022/05/31/golf-courses-in-the-southwest-starting-to- I feel the pain of historic drought
  4. Mayer et al. 1985. Turf irrigation under evapotranspiration replacement as a means of water conservation: Determination of the turf yield coefficient. Pages 357-364. In: F. Lemire, ed. Proceedings of the Fifth International Conference on Turfgrass Research, Avignon, France, July 1985. INRA Publications, Versailles, France.
  5. Turgeon, A. J. Turfgrass Management (9th ed.). Pearson, 2011.

Sean McLaughlin received his MS and BS degrees in Plant Science with an emphasis in Turf Science from Cal Poly Pomona (Pomona, CA). He currently serves as the Golf Supervisor at the University of Southern California (USC) Men's and Women's Golf Facility in Los Angeles.

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