Shizuo Tanaka

Studies on the Develoment and Distribution of Roots and Its Soil Conservation Faculty in Tea Plants : III. Difference of soil retention force of root with variety, planting density and soil moisture

As a soil retention force of tea roots seemed to be influenced by the variety, planting density and soil moisture, the resisting power to stump-pulling was measured using several varieties. The soil retention force of tea roots varied with varieties. Kanayamidori and Okumidori, in which roots were well developed under the ground, had strong soil retention force, but Yabukita and Yamakai, which had comparatively less density of roots and many slender roots, had weak soil retention force. Also, the soil retention power of tea roots varied with the planting density and soil moisture. The denser the plant spacing, the weaker the soil retention force of a plant, however, the stronger was that per unit area. And the soil retention force under much soil moisture was weaker than that under less soil moisture condition.

The Actual Survey of Frost Injury on the Tea Field in the Spring 1972

1. In the spring 1972, the frost injury in the tea field was very severe and it covered wide areas. We carried out an actual survey on the influence on the shoot growth, yield and the price of tea after the injury, and the effects of several preventive measures were researched as occured.2. The frost injury occured all over the country, especially on 2nd, 3rd and 10th April and 3rd May. And the minimum air temprature was -6.0°C at Miyazaki and Nagano prefecture. Therefore, the plucking time of first crop was delayed and the yield of tea was decreased everywhere, accordingly the earning was decreased though the price of tea was dear slightly.3. The degree of injury differed with the condition of locality and the type of cultivation in the tea field. But the relations between these conditions and the injury did not differ when compared with previous survey.4. On the preventive measure of the frost injury in the tea field, the protection methods by covering, heating and fog were adopted from old times, but in addition to these methods the protections by the wind machines and the application of water were used.As the frost protection by covering was effective, the practice of using chemical fibre cloth for protection became more extensive. But when the air temperature was dropped extremely the effect was not perfect though the growth of new shoots after the injury was more rapid than non-covering ones. The protections by the wind machines and the application of water were effective, but they had some doubtful points to the practical use. The protections by heating and fog were not effective.

Reference of the Cover Material for Frost Protection in the Tea Field

To save the frost damage several materials were examined by direct covering on the tea bush.Many kinds of cover material (film type : 5, mat type 9, clothe type : 3, etc) were tested with regard to warm keeping ability on the tea bush surface and the tea leaves.From the result of investigation, polyuretanfoam, BB-tex and lawn with close texture were observed to be effective. Generally direct covering was inferior to indirect covering (covering height was above 50 cm. over the tea bush surface) in keeping warm, so the material for direct covering was required to be inconductive of heat and to be thick somewhat.On the prevention of frost damage by covering the degree of keeping warm was correlated to the degree of thermal inversion and the air temperature near by the tea bush surface.The more the degree of thermal inversion and the lower the air temperature just above the tea bush surface, the larger the warm keeping ability. These facts were very favourable for preventing frost damage.

Studies on the Prevention of Frost Damage in the Tea Garden : IV. On the Height of Covering for Warm the Keeping

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.

Studies on the Prevention of Frost Damage in the Tea Garden : III. On the influence of the direct covering to the air and leaf temperature under the covering

On the preventing frost damage of the tea bush by thin straw mat covering the warm keeping effect was compared between two methods, one was putting the mat on the bush surface (direct covering), the other was holding the mat 60 cm. apart from the bush (indirect covering), the former of these frequently could not prevent severe damage. The air and leaf temperature under the either covering method were kept higher than that in the open plot, especially those under the indirect covering were much higher. The straw mat covering was more effective on a calm night than on a windy one. The difference of air temperature between direct covering and open plot was small, as the bush under the covering was influenced by the radiate cooling from the colder covering material. The leaf temperature under the covering was kept higher than open one, but the touched leaf to the covering material was colder than that of the untouched. These fact suggested that the cold mat more influenced on the air and leaf temperature owing to its nearer situation, and the touched leaf was cooled by heat conduction from colder covering material.

Studies on the Frost Damage on the Tea Bush (Part 5)

1. To know the suitable method to prevent frost damage of the tea bush by thin straw mat covering, the warm keeping effect was compared between two methods, the one was putting the mat on the bush surface (direct covering), the other was holding the mat 60 cm. above apart from the bush (indirect covering).The former method have been said that it frequently could not prevent severe damage.2. The leaf temperature under the covering was both kept higher than that of open one, but the temperature of the leaf touched to the covering material was lower than that of the untouched. From these facts it was suggested that the cold mat influenced on the air and leaf temperature owing to its nearer situation, and the touched leaf was cooled by heat conduction to the colder covering.The air temperature under either covering method was kept warmer than in the open plot, and especially the air temperature under the indirect covering was warmest. The straw mat covering was more effective at a calm night than at a windy one.The difference of air temperature between direct covering and open plot was small, as the bush under the covering was influenced by the radiate cooling from the cooler covering material.3. In the test of 1959, the tea leaves of open and two kinds of covering plot were damaged severely, as the test field was exposed to the low air temperature (about -6.0°C.). But the growth of bud after the damage of indirect covering plot was more speedy than that of direct covering or open plot, and the difference of growing speed between the direct covering and the open plot was seen scarcely.