Studies on the Frost Damage on the Tea Bush (Part 6)

Abstract

1. As the warm keeping effects varied with the height of cover from the tea bush surface in the frost prevention, the suitable height of cover was investigated.2. When the straw mat was covered at the height of 30, 60, 90 cm. above the tea bush surface, the air temperature under the cover was kept warmer at any height than the open plot and especially the 60 cm. covering was kept warmest. Considering the vertical distribution of air temperature under the cover, this phenomenon was explained as follow. Under the 30 cm. covering, the straw mat was put under the inversion layer and the temperature was very lowered and the down-ward radiation was decreased and its warm keeping effect was less than the other plots, influenced by the diffusion of cold air.While under the 90 cm. covering, the temperature gradient of inversion layer was very sharp and the air temperature on. the tea bush surface was lower than that of the 60 cm. covering. From these facts, it was thought that the flowing air entered from the outside of the cover.3. With the same covering material, the warm keeping effect was higher and the radiation balance was less in the high covering than in the low one.Therefore, the second test was carried out on, the influence of the flowing air upon the warm keeping effect when the height and method of covering was varied.The air temperature under the -complete covering was kept higher under the high cover than under the low one, but in the case of the upper side covering, no differnce was observed between the air temperature under the high cover and the low one.The horizontal distribution of air temperature under the high (120 cm.) cover was lower at the wind-ward side than .the lee-ward side. By these facts it was made clear that the warns keeping effect was influenced easily by the flowing air under high cover without side cover.