Expanding-Disk Rain Sensor Dry-Out and Potential Irrigation Savings

Rain sensors are devices that connect to automatic irrigation systems to interrupt scheduled irrigation events as a result of rainfall. The objectives of this study were to evaluate the dry-out time of expanding-disk rain sensors and determine potential irrigation savings under several virtual irrigation schedules. Five rain sensor model/rainfall set point combinations were evaluated at a research site in north central Florida. The five configurations that were compared were Mini-Clik rain sensors with set points of 3, 6, and 13 mm (3MC, 6MC, and 13MC), the Wireless Rain-Clik (WL) rain sensor, and Toro rain sensor at 6 mm setting (6T). The evaluation period ranged from 1,150 days to 1,182 days across the various devices. For each configuration, data for each time a rain sensor switched between allow irrigation to interrupt irrigation modes were collected and compared with how long each stayed in interrupt mode and how much irrigation water a rain sensor could save. Changing the dry-out vents from fully open to fully closed increased the dry-out time by 14% (3 h) but had no influence on irrigation savings. The hygroscopic disks significantly dry out 2 or 3 h after decreasing relative humidity and increasing temperature and solar radiation. Frequent irrigations such as 3 days/week or higher schedules had more potential savings than less frequent schedules. Savings for the WL, 3MC, 6MC, 13MC, and 6T treatments were 9, 11, 5, 8, and 5%, respectively, compared with a schedule without a rain sensor. Lower set points trended toward higher percent irrigation reduction. Six irrigation schedules were included in the analysis with irrigation depth following University of Florida Institute of Agricultural and Food Sciences net irrigation requirement recommendations: 1, 2, 3, and 7 days/week with changing irrigation depth based on recommendations, homeowner (HO, 2 days/week irrigation year round at annual peak ET), and without rain sensor (WORS, 2 days/week). Comparing schedules with WORS, the average percent water savings for 1, 2, 3, 7 days/week, and HO were 6, 8, 10, 28, and $-28\%$, respectively.