Automation of an Intermittent Overhead Irrigation Frost Protection System for an Apple Orchard

An automated sprinkling frost protection system was developed and tested to reduce the environmental damage caused by excess irrigation. A computer algorithm made the initial “turn-on” decision, cycled the irrigation, and turned off the system when the frost event ended. The sprinkling turn-on decision is based on bud stage of development, air temperature, wind speed, relative humidity, and rate of temperature fall. Sprinkler on-off cycles were used to adjust for a recommended sprinkler application rate determined by an energy balance model. The automated system was tested on an apple orchard during one spring and two fall frost events in 1992 and two spring frost events in 1993. The system successfully kept the apple flower bud temperatures above the critical bud temperature during two of the four frost events, while the bud temperatures dropped below the critical values for short durations on the other two events. The system has the potential to save water as indicated by a water use reduction of 75% during one mild frost event compared with the conventional approach of continuous sprinkling.