Off the Record: How soil sensors are revolutionizing fairway watering
In September, USGA-Davis committee members visited the University of Minnesota. Josh Friell, Ph.D., presented progress from their on-course project to encourage the adoption of precision irrigation technology. His research team wanted to quantify changes in water consumption relative to typical practices using evapotranspiration (ET-based) and soil moisture sensor (SMS-based) irrigation scheduling.
Several years ago, we asked Dana Lonn at Toro what had happened to PrecisionSense. Long before, on a USGA research visit to the University of Georgia, USGA research committee members saw a very rough prototype of the PrecisionSense put together by Bob Carrow, Ph.D.
The prototype had a rotating arm that swung around and plunged into the fairway, using time-domain reflectivity and penetrometer probes to obtain soil moisture and compaction. On the back end of this machine was a Greenseeker that recorded the normalized digital vegetation index, a measure of turfgrass canopy health.
Carrow suggested that the awkward-looking device would revolutionize golf course irrigation. Superintendents could run the machine behind a work vehicle for the first time and log the spatial variability for soil moisture and compaction and how it impacted turfgrass health. Established irrigation zones would have soil moisture sensors installed to help determine the next irrigation event.
When we visited Friell at the GCSAA Conference, he reported that PrecisionSense usage was languishing. We thought maybe the USGA could set up some research on golf courses and see if the technology could improve our ability to conserve water.
After a few false starts, the results were finally in, and they were exciting thanks to Friell collaborating with Chase Straw, Ph.D., Ryan Schwab and Eric Watkins, Ph.D. They set up experiments on nine holes at Edina CC in Minnesota. They selected nine fairways, then grouped three fairways based on size, soil moisture descriptive statistics and spatial maps of soil moisture variability.
Each grouping of three fairways is one replication in the study, and each fairway within a grouping was assigned one of three irrigation treatments initiated in 2020. Irrigation scheduling treatments are SMS-based, ET-based and traditional scheduling by the superintendent.
The soil moisture sensor placement was determined using two course surveys conducted with the Toro PrecisionSense (PS6000). Those surveys provided field capacity-based segmentation and classification (low, moderate or high soil moisture) of fairways assigned to the SMS-based treatment.
One Toro TurfGuard in-ground SMS was placed in each soil moisture class within each replication for nine sensors. In 2020 and 2021, they completed two irrigation runs for three holes using weather station replacement ET, three using SMS and three determined by the superintendent.
The superintendent and SMS-based did better than the ET replacement. The good news is that an experienced superintendent can do an excellent job, but SMS can do even better. It comes down to recognizing the spatial variability in golf course soils, and mapping improves our ability to irrigate zones appropriately.
The two-year average mm per week results for irrigation runs in 2020 and 2021 were 7.81 mm for the ET method, 5.57 mm for the superintendent and 4.22 mm for the SMS. This result is a 29 percent decrease for the superintendent and a 46 percent decrease for SMS-based irrigation.
SMS-based irrigation scheduling achieved significant water savings. Due to the humid climate and the superintendent’s professionalism and talent, the traditional scheduling approach used significantly less water than the ET-based treatment.
Mike Kenna, Ph.D., retired director of research, USGA Green Section. Contact him at
mpkenna@gmail.com.
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