Establishment of a Water-saving-type Sprinkler System to Maintain the Temperature of Tea Leaves above the Critical Temperature after Freezing of Water

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  • 水が氷結後にチャ芽に凍霜害が発生しない温度域で葉温を制御する節水型防霜法の実証
  • ミズ ガ ヒョウケツ ゴ ニ チャ ガ ニ トウソウガイ ガ ハッセイ シナイ オンドイキ デ ヨウオン オ セイギョ スル セッスイガタボウシモホウ ノ ジッショウ

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Abstract

In the initial stage of frost protection by using sprinklers for water application, the surface temperature of the tea canopy usually drops to the critical temperature of -2 °C, which causes freezing damage in new shoots of tea, and then suddenly rises to the freezing point of water 0 °C. Thus far, this first decline in temperature has been attributed to insufficiency of water for application. However, we conducted this study by considering the possibility that this decline was associated with supercooling. The conclusions were as follows. <br>1. Distilled water that contained new shoots of tea supercooled in incubator as same as suspension of ice nucleation active bacteria. <br>2. New shoots of the first tea crop in supercooled water were not damaged even at -3 °C, but were damaged when the temperature of the tea leaves dropped below -1.1 °C after freezing of water. <br>3. We developed a new water-application system in which irrigation starts if the surface temperature of the tea canopy drops below -0.4 °C and stops if the surface temperature rises above -0.3 °C for 3 min; we also conducted field frost-protection experiments. <br>4. The use of the new system in the spring of the year 2011, which had frequent hard frost, prevented frost-induced damage in tea shoots. In addition, with the use of the system, there were few instances of water application when the tea leaf temperature did not decline below -0.4 °C. Furthermore, the water consumption by the system in the spring of 2011 was 23% less than that of a 100-s rotation application system popular in Soo in Kagoshima Prefecture. <br>Our data indicated that freezing-induced damage of tea shoots did not occur in the supercooling water if the temperature of the tea leaves dropped below the freezing point of water. Our water application system, which helped maintain the tea canopy temperature above its critical temperature, proved highly effective with regard to frost protection and water consumption.

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