Modification of Water Application Rates and Intermittent Control for Sprinkler Frost Protection

Abstract

Abstract. To validate the feasibility of an automated frost protection sprinkler system, a sprinkler irrigation system with an optimal water application rate was designed, constructed, and tested in a tea field. A modified calculation model of the water application rate was provided by simulation with different values of airflow velocity, air temperature, air humidity, and spray water temperature. An intermittent control strategy was provided using a modified model that included the start and stop time of the system and adjustment of the water application rate. Tea field experiments were conducted to evaluate the effect of frost protection based on this control strategy during frost night events. The results showed that a variable water application rate was better suited for frost protection, and the modified intermittent control automatically regulated the water application rate. In early spring and winter heavy frost nights, the canopy temperature (Tc) of the irrigated area remained above -1.2°C and 0°C, respectively, which is higher than the critical damage temperature for tea plants. The Tc of the irrigated area was approximately 2.8°C higher than that of a non-irrigated area. Moreover, the irrigated area with the modified model had a slower temperature rise after sunrise compared with the non-irrigated area, which was beneficial for frost protection. This sprinkler control strategy is an effective frost protection method that could be applied for in tea fields in the Yangtze River region. The calculation and simulation procedure of the water application rate would be applied for constructing sprinklers for different micrometeorological environments. Keywords: Frost protection, Intermittent control, Spraying water temperature, Sprinkler irrigation system, Tea, Water application rate.