Abstract
The warmth keeping effects of the coverings over tea bushes 30, 60 and 90 cm in height above the tops of the plants respectively were investigated for frost prevention. The effect of that of 60 cm height was the largest. Under the 30 cm covering the air temperature was lowered, owing to that the straw mat was put just below the inversion layer and the air temperature under in was influenced by the diffusion of cold air. The air temperature under the 90 cm covering was obseved to be lower than that under the 60 cm covering. But, in practice, the warmth keeping effect with the same covering material should be higher under the high covering than under the low one. Therefore, a test with flowing air was carried out. The air temperature under the high complete covering was found to be kept higher than under the low one. But no difference in air temperature was observed under the high or low coverings only on the top side, and in regard to the horizontal distribution of temperature, that under the high covering was lower at the wind-ward side than at the lee-ward side. Therefore, we recognized that the warmth keeping effect was influenced easily by flowing air under the high covering without side walls.
