Abstract
Nitrogen absorption by mature tea plants was examined under different nitrogen levels. The annual increase rate of dry matter of five-year-old plants was 1.49 when no nitrogen was applied and increased with increasing nitrogen levels. The increase rate of seven-old tea plants decreased to one-half of that of five-year-old plants and differed a little among nitrogen levels. This means that seven-year-old plants have grown to the mature stage. The increase rate of dry matter of plants applied 180 kg 10 a-1 of nitrogen annually became lower than that of plants given 60 kg 10 a-1 of nitrogen. The amount of nitrogen uptake in five-year-old plants was 30 to 43 kg 10 a-1yr-1, but decreased 23 to 27 kg 10 a-1yr-1 in seven-year-old plants. Approximately 10 kg 10 a-1yr-1 of the nitrogen absorbed was estimated to derive from soil nitrogen produced by the decomposition of organic matter. When 60, 120 and 180 kg 10 a-1 of nitrogen was applied to seven-year-old plants, the uptake efficiency of nitrogen was 21.5, 13.8 and 9.9%, respectively. The amount of 15N absorbed after autumn application was so small that the ratio of the contribution to the first crop of the next year was 5 to 10%. However, the greater the amount of nitrogen supplied in both autumn and spring, the greater the amount of 15N was absorbed, and every organs showed a higher ratio of contribution. However, the nitrogen content of stems, thick roots and white roots remained at a lower level in the heavy applied plot. This was considered to be attributable to the root damage caused by a high concentration of salts in the rhyzospheres that results in restriction of nitrogen absorption.
