Distribution uniformity (DU) has been the long-standing evaluative consideration for an irrigation system’s efficiency, but the DU only has so much impact on soil moisture consistency across golf course irrigated areas. Improving soil moisture consistency is the fundamental goal for golf courses that are looking to maximize water use efficiency and optimize playability. Focusing on moisture uniformity (MU) is much more impactful for superintendents that are working to provide firm playing conditions, healthy turf and efficient water use.

An irrigation system that delivers high DU – i.e., greater than 80% – does not guarantee high MU across a golf course. There are many reasons for this, but at the top of the list are soil spatial variability, wind, slope, sunlight exposure, shade and compaction. Preliminary results from a field study in Texas (Young et al., 2019) indicates high variability in soil spatial characteristics such as bulk density, soil volumetric moisture content and infiltration rate. With such high variability, it becomes clear why there is so much moisture inconsistency across fairways and roughs. While an irrigation system operating at very high DU may deliver high MU indoors and on a flat surface, we have learned that on golf courses the DU does not correlate well to MU.

What is one of the first things superintendents do following installation of a new irrigation system? They change station percentages and adjust cycle and soak times to optimize turf quality and soil moisture! These adjustments are made daily, especially in areas of the west where turf water demand is met almost entirely through irrigation and with almost no help from precipitation.

Optimizing MU is a function of careful irrigation management and utilizing cultural practices to improve soil’s ability to accept water. The objective of this article is to provide five irrigation management strategies that are delivering improved MU at courses in the Southwest where water is limited, water quality is often poor, and water budgets are generally higher than anywhere in the country. If these strategies are working well in such a challenging irrigation setting, they will almost certainly prove beneficial wherever your course is located.

1. Deep watering

You have all heard of the “deep and infrequent” irrigation strategy. However, many do not use this strategy outside of putting greens. Frequent and shallow watering limits gas exchange in the upper rootzone, increases compaction, decreases rooting depth and compounds soil moisture variability. Consider that even a new irrigation system can only be expected to deliver water at 80% efficiency – with no wind. Over time, the error in the water delivery is compounded, similar to interest in a retirement account. Watering shallow and often will not successfully improve chronically wet or dry areas. Applying water deeply at routine intervals will improve moisture consistency across the golf course. Deep watering will help overcome irrigation system inefficiencies and soil spatial variability by improving soil moisture in the chronically dry areas, consequently reducing the need for spot watering.

Brian O’Laughlin, superintendent at Annandale Golf Course in California, schedules irrigation at depths ranging from 0.5 to 1.5 inches nightly, depending on the time of year and evaporative demand. The hydraulic limitations of the pump system and pipe size do not allow O’Laughlin to irrigate more than about three fairways per night at this irrigation level. In 2020, fairways were irrigated every sixth night. Surprisingly, recently irrigated fairways were not noticeably wetter than fairways irrigated several nights before. Soil profiles revealed deep moisture and deep roots. Moisture consistency across the fairways and roughs was remarkable with very little evidence of overly wet or dry areas.

"O’Laughlin reported a savings of $85,000 in water costs in 2020 using this irrigation scheduling strategy despite a hot and dry year."

O’Laughlin is not alone in his success with deep watering but every course must employ a slightly different tactic. At Annandale, full-circle sprinklers are programmed to run at least 30 minutes and part-circle sprinklers run for 15 minutes as a baseline, with individual run times varying based on site-specific conditions. For example, sprinklers in low areas may only run 10-15 minutes while heads on south-facing slopes may run up to two hours. Soak times are set at 15-20 minutes. Courses with poorly drained soils may have to start with run times at only seven to 10 minutes with soak times at 20-25 minutes to avoid runoff. Additionally, courses that have had success with deep watering all note that they started with a goal of applying only 0.3 to 0.5 inch of water for one evening and gradually worked up to higher water volumes. Gain confidence by experimenting with one hole, maybe a par-3 fairway, and utilize deep watering over a four- to six-week period before expanding to the rest of the golf course. The deep watering strategy is one that has proven results and superintendents report annual water use is either unchanged or slightly lower when compared to using a frequent and shallow watering schedule. O’Laughlin reported a savings of $85,000 in water costs in 2020 using this irrigation scheduling strategy despite a hot and dry year.

2. Soil moisture sensing

A high percentage of courses use hand-held moisture meters to help manage water on putting greens.  However, if the golf industry is going to significantly reduce water use and improve soil moisture consistency across fairways and roughs, the adoption of in-ground moisture sensors is the next frontier. There are a few early pioneers using in-ground moisture sensors to schedule irrigation in fairways and roughs. Tyler Truman, golf course superintendent at Sun City Palm Desert, is one of those pioneers. Tyler has been using the Toro TurfGuard sensors for the past four years and has installed four sensors across 40 acres of fairways on the Santa Rosa golf course. Sensors were placed into representative “dry”, “moderately dry”, “moderately wet” and “wet” areas determined by mapping the fairways using the Toro Precision Sense 6000 tool. The turf care team review the sensor data daily, in addition to field scouting and monitoring evapotranspiration data, to schedule irrigation. This strategy has yielded more consistent moisture conditions across fairways and roughs and has resulted in a 10%-14% water savings which translates into an equivalent savings in electrical costs associated with pumping.

The Prestwick Country Club in South Carolina has enjoyed similar success using soil moisture sensors to guide irrigation scheduling decisions. The course has seen a 25% reduction in water use and electrical consumption after installing in-ground soil moisture sensors.

Several USGA-funded research studies have also demonstrated significant water savings when using in-ground soil moisture sensors to schedule irrigation compared to using ET data or a calendar-based schedule. A three-year study at the Rocky Ford Turfgrass Research Center in Manhattan, Kansas, has shown remarkable water savings after two years of study. The total water applied when utilizing data from in-ground soil moisture sensors during the 2019 summer growing season on zoysiagrass turf was 80% less than a calendar-based approach and 44% less than irrigating the zoysiagrass at 60% of reference ET. The repeated study demonstrated similar results in the summer of 2020 where the sensor-based irrigation schedule delivered 84% water savings compared to a calendar-based approach and 72% savings compared to the 60% reference ET irrigation.

A study at California State Polytechnic University, Pomona, has shown that hybrid bermudagrass irrigated with the use of soil moisture sensors resulted in less water applied than plots irrigated based on ET data. Data was collected from April 1 through October 31 in 2018 and 2019. All plots, regardless of water inputs, yielded acceptable quality and turf cover.

Finally, a collaborative study between the University of Minnesota and the Toro Company is evaluating water inputs using in-ground soil moisture sensors compared to traditional (observational) and ET-based irrigation scheduling at 60% of reference ET. This study is different from others because it is being conducted on a golf course – specifically on nine fairways at the Edina Country Club in Edina, Minnesota. Soil moisture maps were produced using the Toro Precision Sense 6000. Low, medium and high soil moisture class categories were established on each fairway and soil sensors were placed in each moisture zone. In the soil moisture sensor treatments, irrigation was triggered when plant available water decreased by 50% in each moisture classification. The plant available water was determined by the difference in soil moisture content at field capacity – i.e., soil water content about 48 hours after a rain or saturating irrigation event – and permanent wilting point, which was determined when wilt becomes apparent to the superintendent. The study has only one year of data collection, but 2020 results indicate 50% water savings in the soil moisture sensor treatments when compared to areas irrigated using the deficit ET strategy.

3. Supplemental irrigation

Hand watering, while necessary and marginally effective, does not deliver the moisture uniformity and depth that can be achieved with low-precipitation portable sprinklers. The Desert Mountain Club in Scottsdale, Arizona, uses low-precipitation sprinklers effectively, despite very efficient irrigation systems. A trailer is used to store and carry sets of portable sprinklers around the golf course for targeted irrigation. The Martis Camp Club in Truckee, California, uses portable low-precipitation sprinklers daily during the growing season. Scott Bower, director of operations, noted that they have assembled 36 sets of portable sprinklers and place two sets on each hole for easy deployment. They run the sprinklers off the central irrigation network ahead of play in the morning and also deploy them following fairway mowing. They set the units along cart paths and strategic areas in the rough during play. The team take turns running the portable units for 30 minutes at a time. While this may sound like a simplistic approach, do not underestimate the value of low-precipitation portable sprinklers if they are used routinely.

Subsurface drip irrigation is another underutilized irrigation strategy. A growing number of courses use drip to irrigate bunker faces. This application has been successful to improve moisture consistency and turf health in bunker perimeters while reducing water use. Teeing grounds are another excellent location for this technology. A study initiated in April of 2016 at The Club at Las Campanas in Santa Fe, New Mexico, has demonstrated excellent results using subsurface drip irrigation for teeing grounds. This study has been a collaboration with Tom Egelhoff, director of agronomy at Las Campanas, Dr. Bernd Leinauer and his team at New Mexico State University, the USGA, Toro and Rainbird. Drip lines were installed on a 12-inch spacing, 5- to 6-inches deep, in a sand-based rootzone. The results have been extraordinary. Water use is 60%-80% less than with overhead irrigation. Labor for trimming and removing undesirable vegetation adjacent to the island tees has been nearly eliminated. Last year the turf team documented significantly better moisture uniformity on the drip-irrigated tees. In fact, the moisture uniformity – calculated by collecting a grid of soil moisture values with a hand-held meter – was easily over 80% on drip-irrigated tees and only 60%-75% on overhead irrigated tees. On one drip-irrigated teeing ground the moisture uniformity was over 90%. The USGA article “Subsurface Drip Irrigation Reduces Water Use on Tees” provides more information about this important study.

Given the success of this project, the club leadership approved funding to install subsurface drip irrigation on all tees on both courses. Additionally, Dr. Leinauer and his research group recently expanded the use of drip irrigation to a sloping area in the rough at Las Campanas.

4. Wetting agents

Wetting agents improve moisture consistency, especially in sand-based systems. The USGA Green Section Collection “Understanding Wetting Agents” has extensive resources on wetting agent use, so this article will not discuss the topic in detail. Rather, the message here is the importance of using wetting agents throughout the growing season to reduce water use while maintaining quality turf. A two-year study at the University of California, Riverside, evaluated the ability of mineral oil and two wetting agents to improve turf quality and increase soil volumetric water content. The study revealed that: “All tested products could maintain acceptable quality for at least 12 weeks when irrigated at 55% reference ET replacement, better than the untreated control.” Both research and field use suggest that wetting agents can improve moisture uniformity, increase moisture content, and can offer acceptable turf quality under deficit irrigation. Wetting agents will not reduce water use on their own – golf course superintendents must do that through irrigation decisions. However, superintendents applying wetting agents can reduce water inputs and attain the same level of turf health and density.

5. Modify soil and add drainage

There are many courses where the physical limitations of the soil severely restrict water infiltration, resulting in poor moisture consistency, poor playability and compromised turf health. A proven strategy to improve rootzone conditions is sand topdressing. A USGA-funded study (Whitlark, 2014) demonstrated the value of an annual sand topdressing program to improve fairway soil conditions. In this study, all courses that had applied at least 3 inches of sand over several years (an inch of sand is equal to approximately 160-180 tons per acre) saw a remarkable 2,000% increase in infiltration rate. Plant available water increased with sand topdressing by an average of 254% when compared to no soil modification. Although moisture uniformity data is not presented in this study, I can confirm that soil moisture consistency has improved for those courses who have modified their poor soils. This is not to say that sand topdressing is for everyone and it is strongly recommended to work with a physical soil testing laboratory before initiating a fairway sand topdressing program.

Improving surface and subsurface drainage is another key strategy to improve moisture uniformity. A good drainage network allows for increased site-specific watering on mounds and south-facing slopes without creating saturated conditions in low-lying areas. For additional information on surface and subsurface drainage, please read the USGA article “No Drain No Gain.” 

Conclusion

It takes diligence, daily observation, constant adjustment and a good plan to optimize moisture uniformity across a golf course. The work is never done as the weather is constantly changing, sun angle changes dramatically from winter to summer and sprinklers fall out of adjustment – to name just a few of the variables involved. Hopefully, the strategies in this article will prove useful to improve soil moisture consistency at your golf course.

Looking for site-specific recommendations to improve moisture uniformity at your course? USGA agronomists work closely with golf course superintendents through the Course Consulting Service to provide practical recommendations tailored to your facility.

Brian Whitlark is a senior consulting agronomist in the West Region.

References:

Bremer, D. 2016. “Small unmanned aircraft systems detect turfgrass drought.” USGA Green Section Record. April 1. 54(7).

Dyer, W., D. Bremer, A. Patrignani, J. Fry, J. Hoyle, and J. Friell. 2019. “Comparison of irrigation scheduling methods.” 2019 Research Summaries, USGA Turfgrass and Environmental Research Program. pp. 230-234.

Evans, S., C. Campbell, B. Hopkins, and N. Hansen. 2016. “Water use in turfgrass using sensor-driven decisions.” Presented at Resilience Emerging from Scarcity and Abundance. November 6-9.

Saxena, P., R Green, E. Vis, and V. Mellano. 2019. “Soil moisture sensor irrigation scheduling in bermudagrass.” 2019 Research Summaries, USGA Turfgrass and Environmental Research Program. pp. 220-222.

Straw, C., J. Friell, and B. Horgan. 2018. “Encouraging adoption of precision irrigation technology through on-course application and demonstration of water savings.” 2018 Research Summaries, USGA Turfgrass and Environmental Research Program. pp. 228-235.

Young, J., S., Deb, G. Ritchie, W. Guo, E. Escamilla, J. Cantu, and D. McCall. 2019. “Enhancing water conservation with remote sensing technology on golf courses.” 2019 Research Summaries, USGA Turfgrass and Environmental Research Program. pp. 235-239.

Whitlark, B. 2014. “Winning strategies to overcome adverse soil conditions.” USGA Green Section Record. July 25. 52(15).