Studies on the Root Rot Disorder of Tea (Part 4): The Alteration of pH and Fine Root Deterioration in Nishio Tea Soils

1. In a preliminary survey of soil, high level of pH of tea soils was sometimes encountered in Nishio district where the root rot disorder of tea was severely occurring. Studies were initiated to obtain informations concerning (1) variation of pH among tea fields in relation to the depth of soil and the seasons, (2) cause of the increase of soil pH, and (3) correlation between soil pH and deterioration of tea fine root. 2. The distribution patterns of soil pH from 3 depths, 0-10 cm., 10-20 cm. and 20-30 cm., were shown to be generally unchanged in every soil at 6 times throughout a year, and it seemed that every soil had a characteristic pattern of soil pH. These patterns were divided essentially in 2 types ; i. e. the pH of upper soil increased markedly than those of lower soil and significant difference of pH was riot observed among the soils from each depth. Further, the former was classified into 4 types in details. 3. Though applications of calcium cyanamide, limes and chicken manure were not reflected sharply on the soil pH, there found a trend that a great deal of these materials increased pH of upper soil. 4. Soil pH decreased to some degree at June and September in every soil. In the same field, the soil pH increased as came nearer to the soil surface. These results could be recognized in relation to the fertilization. The pH of the second layer soils (10-20 cm.) was closely resemble to that of the first layer (0-10 cm.) in some soils and in the others to the third (20-30 cm.). The trend was presumably affected by the cultivation technique, i. e. ploughing and fertilizing. 5. There was a tendency that the buried tea fine root in soils having various pH deteriorated severer as the soil pH increased, though the soil pH itself could not be directly connected to the damage. Correlation coefficient of r=0.679* was calculated between the soil pH and the Deterioration Index. The deterioration of fine root occurred generally poor in soils in June. It was found apparently that a high level of soil pH was a condition in which the deterioration of fine root was apt to occur in the Nishio tea soils.