Temperature variability during frost event on different terrain of tea fields

Abstract. To determine the environmental monitoring points and the layout regularity of frost protection machines in tea fields, the canopy temperature and inversion intensity of six different locations (A-D) were tested during frost occurrence in December, 2013. The heights of the temperature sensors were 1.2m (the canopy), 3.5m and 6.5m above the ground. Subsequently, two wind machines were installed at sites A and D in the spring of 2014 to assess the influence of site conditions on machine starting time and frost protection effect. The results showed that temperature gradually decreased with the reduction of altitude in different terrains and the maximum difference was 6.1°C. The minimum temperature in the tea fields was significantly lower than the minimum temperature from the weather forecast with the biggest difference of 7.0 °C. The thermal inversion between 6.5 m and 1.2 m was 8.2°C, but the intensity of the increased with the decrease of altitude. The wind machine at site A increased the canopy temperature by 1.8 °C in 30 minutes and 3.2 °C in 1 hour. The machine at site D also increased the tea canopy by 3.4 °C in 30 minutes but fell to 2.9 °C in 1 hour. Furthermore, the machines at both sites maintained the tea canopy temperatures above 0 °C throughout the operation period. Therefore, starting wind machines in advance is critical for effective crop frost protection. The early warning systems for frosts and the control of frost protection machine should be decided on the actual environmental conditions.