Takao Fujii

“Professor Fujii conducts research to produce delicious Uji-cha. Production of Japanese tea began in the Kamakura Period (12th century) when green tea was brought from China. While tea is grown throughout Japan, the Uji Region demonstrated remarkable innovations and significantly improved the quality of its tea, establishing itself as a Japanese brand. One of those innovations was the advancement of fertilizer.
In the early Edo Period, the Takase River, which took in water from the Kamo River, was excavated. The water in the Takase River was shallow, and Takasebune boats with flat bottoms carried water to and from the surrounding villages. Various kinds of food were brought from the villages to the capital of Kyoto, and an effective fertilizer known as “night soil” was transported from the capital to the villages. This night soil was transported both to vegetable-producing areas in Osaka and tea-producing areas in Uji, resulting in the stabilization of crop yields and improvement of tea quality. With the advent of such new fertilizers, tea gardens had until modern times applied many fertilizers based on the belief that “quality tea is made from generous fertilization.”

The above explanation serves as a pretext for the following explanation of Professor Fujii’s research. With a high amount of fertilizer applied to tea gardens, there is concern about the outflow of fertilizer components to the environment. Professor Fujii took it upon himself to review the methods and amounts of applied fertilizer. The review begins with questioning whether there is no waste of fertilizer in such fertilizer application methods since tea is a perennial crop and fertilizer is applied year-round. In particular, the research began by clarifying whether fertilizer applied in the previous spring (March to April) or the previous fall (October to November) improves the quality of the first crop of tea harvested in May.
However, when conducting this research, it is difficult to distinguish whether the nitrogen content in shoots that grow during the first crop of tea comes from spring or autumn fertilization. To combat this issue, one can have test plots that are “only fertilized in spring” and “only fertilized in autumn” and then compare the contribution of each fertilizer from the nitrogen concentration in the new shoots. However, not applying fertilizer when it should be applied may provide inaccurate data.
Consequently, Fujii’s team considered using stable isotopes of nitrogen. Most nitrogen has an atomic weight of 14, while stable isotopes of nitrogen have an atomic weight of 15. Using this stable isotope of nitrogen, rapeseed was grown by applying ammonium sulfate (a fast-acting fertilizer used in tea) and potassium nitrate, which contains stable isotopes of nitrogen. The rapeseed was collected and squeezed to make an oil cake, which contains stable isotopes of nitrogen.
When nitrogen fertilizer containing stable isotopes with different atomic weights is used, the following test plots are set:

(1) Rapeseed oil cake containing stable isotopes is applied in autumn and normal rapeseed oil cake is applied in spring.
(2) Normal rapeseed oil cake is applied in autumn and normal rapeseed oil cake containing stable isotopes is applied in spring.
(3) Ammonium sulfate containing stable isotopes of nitrogen is applied in mid-April, just before the first harvest of tea.

From there, the concentration of stable isotopes in new shoots of first-picked tea is determined in the test plots of (1), (2), and (3). Although the calculation is somewhat complicated, the amount of nitrogen absorbed from rapeseed oil cake containing stable isotopes of nitrogen in (1), (2), and (3) or from ammonium sulfate can be calculated from the concentration of stable isotopes in the new shoots.
As a result, the highest amount of nitrogen in the first crop of tea shoots was derived from ammonium sulfate applied in April. Professor Fujii found that the fast-acting nitrogen fertilizer was efficiently absorbed in the new shoots that began growing from April onwards. The results suggest that if the contribution of fertilizer applied in the previous fall or the following spring to the first crop of tea shoots is low, it may be possible to reduce the amount of fertilizer applied in that period.

To produce quality tea, another topic that Professor Fujii investigated was finding out why tea gardens are distributed in mountainous slopes of tea-producing regions. Being on a mountainous slope, the environment for management and harvesting in tea gardens is not always favorable. There must be a reason why sloping tea gardens persist in such poor working environments. Professor Fujii’s team conducted a study with the hypothesis that a sloping tea garden is maintained to make tea of high quality.
In the first season of tea, from early to mid-May, there is an optimal time for harvesting that will lead to the production of higher quality tea, and that optimum interval lasts about three to five days, depending on the variety. If the same variety is planted over a large area in the same environmental conditions, there is a greater chance it cannot be harvested at the right time due to the amount of time it will take to cover such a vast area. The temperature in a sloping tea garden varies depending on its elevation, allowing the distribution of the right time for picking. A survey of the working conditions of tea growers revealed a close relationship between the elevation of the tea garden and the day of harvest; the higher the elevation, the later the harvest. In other production areas, flat tea gardens have been created to prioritize the efficiency of tea garden management. However, Professor Fujii found that the main reason for the maintenance of tea gardens on mountainous slopes is that they are always picked at the right time to produce tastier tea. Based on the dispersal of picking time due to the difference in elevation of tea gardens, it has been found that the combination of varieties, which means variation in the speed at which new shoots grow, is also effective in dispersing the optimum harvesting time.”