*2.2. Irrigation Trials*

The responses of hybrid bermudagrass ['Latitude 36' *Cynodon dactylon* (L.) Pers. × *C*. *transvaalensis* Burtt-Davy] and tall fescue [a blend of 'PennRK4', 'Rebel XLR', + 'Firecracker SLS' *Schedonorus arundinaceus* (Schreb.) Dumort.] to six irrigation treatments (3 irrigation levels × 2 irrigation frequency restrictions) were studied. A total of 36 plots (3.7 m × 3.7 m) formed two adjacent trials organized in a factorial randomized complete block design with repeated measures over time. Table 1 summarizes the irrigation treatments. The irrigation system was installed and the plots were prepared in early 2017. The turfgrass plots were established with sod in late July 2017. For several months afterward, the plots were under non-limiting irrigation for root development and grass establishment. A uniformity test was conducted using catch-can devices on 5 August 2017 with wind speed less than 0.9 m s−<sup>1</sup> on eight randomly selected plots. The low half distribution uniformity (DUlh) was 0.78 and the estimated precipitation rate was 23 mm h<sup>−</sup>1.

**Table 1.** Irrigation treatments imposed throughout the 2-year tall fescue and hybrid bermudagrass irrigation research experiments conducted at the University of California Kearney Research and Extension Center.


irrigation efficiency, the programmed irrigation levels (i.e., target ETo levels divided by irrigation efficiency) ranged from 51% to 103%. The watering days were restricted to two (Sunday, Thursday) and three (Monday, Wednesday, and Saturday) days per week in 2018. In 2019, the watering days were changed to 3 (Sunday, Wednesday, and Friday) and 7 days per week. The 7-day treatment represented a no watering restriction scenario

when the smart controller could irrigate as needed based on ETo demand. To avoid light irrigation applications, the controller was programmed to use the default deficit threshold of approximately 4 mm as the lower deficit limit before any irrigation occurs.

The standard cultural practices were followed to maintain the plots throughout the study, including mowing the plots once a week (mowing heights for tall fescue and hybrid bermudagrass were set to 76 mm and 44 mm, respectively), applying fertilizer two times per year in spring and fall for tall fescue and once a year in the early summer for bermudagrass at a typical rate of 49 kg ha−<sup>1</sup> nitrogen each application, and spraying the borders as needed with herbicides to control the weeds. The study was started on 4 May and data collection ended on 11 September in 2018. All plots were switched back to the uniform non-limiting irrigation for recovery before starting the second year of the experiment on 22 June 2019. On 26 August 2019, the main irrigation pipe broke and flooded the field, forcing the research team to terminate the trial.

A Weathermatic Smartline (SL) 4800 controller (Telsco Industries, Inc., Garland, TX, USA) was used to autonomously schedule irrigation. A Weathermatic SLFSI-T10 flow sensor (Telsco Industries, Inc., Garland, TX, USA) was installed and connected to the controller in 2019 to monitor the flow across treatments and detect leaks automatically. The controller used an onsite temperature sensor and latitude-based solar radiation information to calculate ETo using the Hargreaves and Samani equation [17]. The controller used the user-defined "plant type" values and irrigation precipitation rate to calculate irrigation application for each treatment as fractions of ETo and convert it to equivalent run times. The plant type for each treatment was calculated as the target ETo level divided by the efficiency of the irrigation system.

Irrigation was done overnight and early morning to avoid evaporative loss and minimize wind drift. The smart controller performed a run/soak schedule to eliminate runoff and provide enough soak time. All three replications for each treatment were wired to the same zone on the controller to receive irrigation at the same time. Each plot was equipped with a TORO 252 Series solenoid valve (Toro Co., Bloomington, MN, USA). The solenoid valve supplied water to four Toro O-T-12-QP corner-pop-up 6" sprinkler heads (152 mm tall) with an operating pressure range and flow rate of 276–517 kPa and 0.02–9.08 l min<sup>−</sup>1, respectively. The sprinklers had factory-installed, pressure-compensating discs to ensure steady water application (Toro Co., Bloomington, MN, USA).
