Frost Protection Effects And Control Of Wind Machine Technology For Tea Garden

In recent years, tea production has severely suffered from late frost damage in early spring because of the increasing climate deterioration. Conventional methods of frost protection, such as covering, smoking or irrigation are ineffective, labor-intensive and even pollute the atmosphere or tea plants. The method of disturbing air in the thermal inversion layer has proved applicable for frost protection in orchard in Europe, Japan and the USA, which is implemented by wind machines. However, research and development of the method in China is just at the beginning stage. The experiment was conducted to make clear the temporal and spatial distribution of air temperature near ground, which proved the feasibility of frost protection by disturbing the thermal inversion layer in tea garden. Then the working principle and system configuration of wind machine system was analyzed, and the experiment was conducted to show the effecs of frost protection with the wind machine system. Finally the control subsystem of wind machine was preliminarily designed based on critical temperature and wind speed. The main study results are as follows:1. Under temperature inversion in early spring experiment was conducted on south slope, north slope and flat field to measure temperature of horizontal distribution at tea plant canopy, vertical distribution within 7 m above ground and soil temperature diurnal change. The results show that frost tended to happen during a clear night when there was little wind. The frost was heavy between 21:00 and 06: 00, and became the heaviest at dawn (05:00～06:00) .The intensity of temperature inversion changed with height and reaches the highest at 4 m, over which temperature inversion weakens. At night canopy temperature on flat field was the highest while temperature on north slope was the lowest. The temperature on flat and south slope changed slowly, and the temperature on north slope changed rapidly, which was easily influenced by frost and the damage here was the severest compared with south slope and flat field. Moreover, soil temperature at 12 cm depth changed slowly and usually reached the highest at 18:00. The soil temperature of flat field was always higher than that of north slope.2. On thermal inversion nights the wind machine was operated in tea garden and its effective coverage and frost protection effect were confirmed. The results show that the operation of wind machine could remarkably increase the temperature at tea plant canopy, especially when thermal inversion was strong. Within 10 to 25 m in front of the wind machine, tea canopy could be completely prevented from frost. And at 10 m in front of the wind machine the increased temperature reached the maximum of 3.6℃.3. The control subsystem were developed to start or close wind machine automatically according to different climatic conditions. When the temperature at tea plant canopy reaches below 0℃and under the inversion temperature condition,the fan starts automatically. Otherwise, when the temperature at the tea plant canopy gets higher than 0℃or despite lower than 0℃but not satisfy the inversion condition, the fan close automatically.The research proved the feasibility of wind machine to prevent tea plants from frost damage, and control subsystem was designed and developed, which provided a reliable theoretical and practical guidance for further application in tea garden.