This paper describes three investigations of the effectiveness of a frost fan in mitigating the frost damage that occurred on March 30, 2010 in tea fields in Shizuoka. The author presents a detailed map of the distribution of damage that occurred in those fields. The map indicates that the area over which the fan is effective changes with the direction of the westerly wind, and was limited to around 25%-30 % of the designed value.
We conducted a detailed examination of the temperatures of a tea bush throughout the night of severe frost. The temperature was measured at various heights and distances from the frost fans. The surface temperature of a tea bush decrease to -4°C . There little difference between the air temperature at the height of the frost fan motor and the surface temperature of a tea bush.
The growth stage and degree of cold resistance of tea buds were investigated from autumn 2009 to march 2010. Near the end of March 2010, the growth stage of buds was 2 or 3 days earlier than that in an average year and the 50% lethal temperature increased to -4°C . This characteristic value for tea buds might be had a close relation with the severity of frost damage in the spring of 2010.
We urgently studied the influence of pruning shortly after frost damage to new shoots in the early stage of growth on the subsequent first crop in 'Saemidori' tea bush, which had been medium-pruned in the previous year. Shallow-pruning, defined as trimming off about one node of mother stems, made remaining shoots heavier and increased more than 20 percent of yield than no treatment. This result suggested that shallow-pruning enabled early plucking and was expected to diminish the revenue decline caused by frost damage to new shoots early on growth.
In 2010, tea shoots took the freezing damage on March 30 in Shizuoka prefecture. This damage decreased in the yield of fresh tea leaves produced from 14268 ha in the pref. It would be great damage once in 30 years. Besides, this damage brought about 4489 millions yen decrease. Thus, we compiled tea leaves data obtained from the past five years (2006 to 2010) in this short paper. The data included plucking date, characteristics of the fresh and processed tea leaves, as well as the levels of caffeine and catechins. In 2010, the plucking date of early cultivar 'Saemidori' was a few weeks late in comparison with the average year. The characteristics of the tea shoots were small and including terminal bud. Nevertheless, they relatively had many matured leaves. The level of caffeine in the processed leaves was same as that in the other years, but the level of catechins was higher (23.2 %) than those (13% to 19%) of leaves processed in the other years. This may be due to including many matured leaves in the tea shoots plucked. The plucking date of medium cultivar 'Yabukita' was a couple of week late, but the late cultivar 'Okumidori' was plucked as usual. For these two cultivars, significant difference was not found in the characteristics of fresh and processed tea leaves, as well as the levels of caffeine and catechins.
Tea trees planted at the Kanaya Tea Research Station were exposed to spring frost and cold weather on March 30, 2010. In this study, we assessed the frost sensitivity of these tea cultivars. This sensitivity was linked to the time of the bud break. The early bud break cultivars had more severe frost damage than those in the late bud break cultivars. However, ‘Sayamakaori’ had minimal frostdamage as compared to the other cultivars at the same bud break stage. These results indicate that spring frost sensitivity may differ among cultivars at the same bud break stage. It is necessary to develop a novel frost injury-resistance assay for tea cultivars and to develop cultivars that can overcome frost injury.
The tea fields of the Makurazaki tea research station, the National Institute of Vegetable and Tea Science, suffered severe frost injury on March 11, 2010, when subfreezing conditions of the tea canopy surface of 'Meiryoku' continued from 1 am to 7 am. The lowest temperature was -2.9°C at 5:00am. Frost injury of tea shoots was observed in early budding tea cultivars which had sprouted before March 8. Varietal differences in the frost injury of each tea cultivar were also observed. The severity of frost injury of each tea field increased as altitude decreased. Recovery of frost-injured tea shoots of early budded cultivars was observed at the end of the season of the first crop of tea.
We established the method for analysis of tea aroma by using solvent-assisted flavor evaporation apparatus. The solvent dichloromethane (300 mL) is spiked with ethyl decanoate as an internal standard before extraction. The mixture of tea powder (20g) and saturated water with sodium chloride (400 mL) are refluxed at 45 °C for 30 min in triplicate with the dichloromethane (100mL each time). The solvent extract is dried over anhydrous sodium sulfate, and then the solvent is removed by Snyder column to obtain approximately 20 mL. The glass wool (2 g) is inserted to SAFE apparatus for removing interferes, before distillation by using SAFE apparatus (30 °C, 103 Pa). Thedistillate is further concentrated to approximately 0.2 mL by Snyder column and nitrogen stream before the injection to the gas chromatography.