Performance of Rain Delay Features on Signal-Based Evapotranspiration Irrigation Controllers

Evapotranspiration-based irrigation controllers, also known as weather-based irrigation controllers, are a new water-saving technology that use evapotranspiration (ET) estimates to schedule irrigation. Many ET controllers have the ability to incorporate rainfall events into irrigation scheduling using onsite sensors attached to the controller or weather updates through weather-monitoring services. The Toro Intelli-Sense controller can use an onsite rain sensor (rain switch) that immediately interrupts irrigation or a weather service that causes the controller to enter a rain pause mode to incorporate rainfall into irrigation scheduling. Four treatments were created using the combination of rain delay features: no rain delay features (TN), rain pause (TRP), rain switch (TRS), and both rain delay features (TRP-RS). A fixed-time irrigation schedule with a rain switch and a fixed-time irrigation schedule without a rain switch were created for comparison: T, timer with a rain switch; and TWORS, timer without a rain switch. During relatively dry periods (72% below historical seasonal rainfall) neither rain pause nor the rain switch resulted in irrigation reduction. However, during periods of rainfall (84% of historically rainy days), both features resulted in significant irrigation savings. The combination of rain switch and rain pause reduced irrigation 41% compared with the use of no rain features, whereas the rain pause feature alone saved 25%. Because of the variability of rainfall in humid climates, using both a rain switch and the rain pause feature is recommended to delay irrigation on the Toro Intelli-Sense controller.