Soil-Moisture Sensors

Overview

There are many types of soil-moisture sensors (SMS). The most commonly used option on golf courses today are hand-held moisture meters that are typically used on greens, but in-ground sensors are becoming more popular. All SMS provide superintendents with an estimate of how much water is in the soil at a particular location. Superintendents can track this data over time and learn about how their turfgrass looks and performs at various soil moisture levels. This information can then be used to create thresholds for irrigation.

In-ground SMS are well suited for use in large areas like fairways and should be placed in locations that represent common situations on the course – e.g., low or wet areas, dry areas and shaded areas. Using in-ground SMS to represent large areas across the golf course makes it easier to scout and estimate irrigation needs. Portable SMS are more commonly used on putting greens because they are smaller areas that demand higher precision, so users can take many readings with a portable device to optimize watering. 

Benefits and Limitations of SMS

There are several major benefits of incorporating SMS into irrigation management. The first is expected water savings. When compared to calendar-based or ET-based irrigation scheduling, using in-ground SMS to guide irrigation decisions results in 20% to 80% water savings that begin immediately after starting SMS use (Cardenas-Lailhacar & Dukes, 2012; Chabon et al., 2017; Dyer et al., 2021). More-precise water management also means improved playing conditions and healthier turf, and using in-ground soil moisture sensors to develop a representative picture of water needs across the golf course makes scouting more efficient.

Some challenges that come with using SMS devices include spatial limitations, calibration requirements, installation issues and physical damage that may occur after installation. SMS devices can only cover small, representative areas – but there are often high degrees of variability in soil moisture, even within a small area. How representative a particular location may be can also change throughout the year with changes in things like sun angle, shade patterns and temperatures. The usefulness of a sensor in a particular location will need to be continually evaluated. SMS equipment often requires calibration before use and sometimes on an ongoing basis, and there are challenges when installing in-ground sensors. Small mistakes like not fully inserting the rods into the soil create issues with readings. These devices are also exposed to the environment, which can lead to them being damaged and/or giving inaccurate readings.

Remote-Sensing Technology

Overview

Remote-sensing technology includes a wide range of tools that try to quantify plant characteristics and/or soil moisture without making physical contact with the target area. This includes analyzing digital photos or using specialized cameras that measure light reflectance at multiple wavelengths or thermal cameras that measure surface temperature. These tools can efficiently create detailed maps of an entire golf course showing estimates of soil moisture content or plant stress, but the results must be continually “ground-truthed” against actual soil-moisture data and turf conditions to fully understand what the imagery is showing.

Benefits and Limitations of Remote Sensing

Golf courses that have implemented various remote-sensing technologies have reported water savings. These savings can begin shortly after adding this tool to the maintenance program, and the more readings and measurements that are taken, the more useful the data becomes. Additionally, remote sensing provides superintendents with greatly improved scouting abilities. These tools make it possible to gather information about large areas of the course in a relatively short time and provide a viewpoint to see problems and patterns that may not be visible to staff on the ground. A final benefit of these tools is ease of use and implementation. Depending on the technology, it can be quite simple to begin using remote sensing and there are consultants available that can assist with startup and interpretation.

Remote-sensing technology also has some limitations. First, these are relatively new tools in the golf course maintenance world and there is still much to learn about how to optimize the various options and how accurate the information is. For example, early results from some studies have not shown a strong correlation between estimates from certain technologies and measured soil moisture data (Isom, 2024). Additionally, there may be logistical and legal restrictions, especially when aerial drones are involved. One other challenge that may come up with remote sensing is image resolution and processing. Information from a satellite will be less precise than a remote sensing tool that is being driven over the fairways. Processing large files and getting the output in a timely fashion can also be a challenge and often requires professional assistance.

ET-Based Irrigation

Overview

Evapotranspiration (ET) combines estimates of water loss through evaporation from the soil and transpiration from the plant to give a clearer picture of how much supplemental water the grass requires. With this information, irrigation inputs can be refined to more accurately match true water needs. ET data can come from on-site weather stations, ET gauges, or other weather services/networks and is then adjusted for cool- or warm-season grasses with crop coefficients. This approach to irrigation scheduling currently has a relatively low adoption rate, most likely due to unfamiliarity with the process and potential benefits. 

Currently, ET-based irrigation is most used in areas where water conservation is crucial, like in arid regions of the United States, but there are benefits to using this approach for golf courses everywhere. Managing golf courses is becoming increasingly data-driven, and integrating ET data into irrigation planning can increase precision and improve playing conditions, along with the potential for water savings. 

Benefits and Limitations of ET-Based Irrigation

ET-based irrigation can account for factors like local weather, turf species, microclimates, soil conditions and type of playing surface to help superintendents gain a better understanding of daily water needs. Being able to make better adjustments based on the daily conditions at your course leads to increased water efficiency and savings, with research showing as much as 20% to 50% savings over runtime-based irrigation (Serena et al., 2020). ET-based irrigation takes some of the guesswork out of watering, which reduces the risk of applying too much or too little.

Implementing a new approach to irrigation undoubtedly comes with some challenges, and ET-based irrigation scheduling is no different. While there are national and state weather networks that offer free ET data, to obtain the most accurate, site-specific information, an on-site weather station is required. If a course doesn’t already have one, there can be a significant initial setup cost, especially if you want to install multiple weather stations to account for varying microclimates on the property. Aside from cost, there can be process challenges when switching to ET-based irrigation. Superintendents and their staff will likely need training to understand ET data and how to adjust irrigation accordingly, and setting the irrigation control system to water properly based on ET data can be complicated at first. 

Conclusion

New tools for site-specific irrigation make assessing water needs more efficient and accurate than ever before. Beyond the water savings that can come with using these tools, playing surfaces will be firmer and more uniform, turf will be healthier, and superintendents will gain an even deeper understanding of how to best manage their course. 

References

Cardenas-Lailhacar, B., & Dukes, M.D. (2012). Soil moisture sensor landscape irrigation controllers: A review of multi-study results and future implications. Transactions of the ASABE, 55(2), 581-590.

Chabon, J., Bremer, D.J., Fry, J.D., & Lavis, C. (2017). Effects of soil moisture-based irrigation controllers, mowing height, and trinexapac-ethyl on tall fescue irrigation amounts and mowing requirements. International Turfgrass Society Research Journal, 13(1), 755-760. https://doi.org/10.2134/itsrj2016.04.0242

Dyer, W., Bremer, D., Patragnani, A., Lavis, C., & Friell, J. (2021). Integrating canopy dynamics, soil moisture, and soil physical properties to improve irrigation scheduling in turfgrass systems. USGA Turfgrass and Environmental Research Online Summary, pp. 214-221. https://archive.lib.msu.edu/tic/ressum/2021/2021.pdf

Isom, C. (2024). Making sense of remote sensing. USGA Green Section Record, 62(14).

Serena, M., Velasco-Cruz, C., Friell, J., Schiavon, M., Sevostianova, E., Beck, L., Sallenave, R., & Leinauer, B. (2020). Irrigation scheduling technologies reduce water use and maintain turfgrass quality. Agronomy Journal, 112(5), 3456-3469. https://doi.org/10.1002/agj2.20246