Studies on the Volcanic Ash Tea Soils (Part 1): Soil Development of Tea Field as Related to Passing Years after Planting

For clarifying the characteristics of the tea soil derived from humic volcanic ash soil widely distributed over the southern Kyushu, some chemical and physical properties of the different aged tea soils were compared with those of the cultivated and uncultivated soils. 1. It was observed that the vegetation and the mulching practice in tea gardens gave considerably profound influences on the moisture condition and the moisture permeability of the soil. 2. The eluviation of the clay mineral and its accumulation in the lower horizon were not observed in every tea soil. On the contrary, the clay content in the surface. layer of the old tea soil was larger than in that of the young tea soil. It was supposed that the tea vegetation and mulching gave favorable effects on the acceleration of soil weathering as well as on the protection of soil erosion of the surface soil. 3. The accumulation of the organic residues in the surface layer of the tea soil was observed and the cation exchangeable capacity of the soil increased with increasing clay content in it. 4. When newly planted with tea, the soil was rapidly acidified, especially in the root zone. 5. The exchangeable Ca and Mg content of the soil rapidly decreased by the tea vegetation in the humic volcanic ash soil, especially the latter content remarkably decreased, but the exchangeable K content of the tea soil was more than that of the cultivated soil. These phenomena were supposed to be caused by the customary tea manuring way in which the tea soil was usually supplied with much K and less Ca and Mg. 6. Total P content in the surface layer of the tea soil was more than in that of the cultivated soil, and its content increased in the lapse of years. The ratio of inorganic P/total P of the tea soil was larger than that of organic P/total P. The inorganic P, derived from fertilizer and fixed in soil, was accumulated a large quantity in the surface layer of the old tea soil, consequently the phosphorus absorption coefficient and the disolubility of aluminum decreased. There was no remarkable difference in the content of fractionated P among three kinds of soil. In every soil, Al-hound and insoluble P were contained abundantly, while Ca-and Fe-bound P were negligible except in the surface layer of mature tea field. The largest quantity of organic P was contained in the first layer of tea soil while in the cultivated soil, it was contained in the second layer. 7. The tea soil contained much more water soluble Al