Analysis of Yield-Determining Process and Its Application to Yield-Prediction and Culture Improvement of Lowland Rice : CXVII. The effects of the growth potency (amount) at the starting time of the nitrogen restriction treatment and the nitrogen concentration of nutritional solution during the treatment on the further growth of rice plants

[摘要] In the previous paper, the authors estimated that the effect of the nitrogen depletion treatment on the further growth might vary according to the growth potency (e.g., growth amount such as the dry weight of plants or the number of tillers) at the starting time of the treatment and the length of the treatment. From the same point of view as in the previous paper, furthermore, the authors tried some experiments to clarify the effect of the growth potency at the starting time (70 in leaf number index) of the nitrogen restriction treatment and the nitrogen concentration of nutritional solution during the treatment on the further growth of rice plants. Achieving this purpose, the rice plants with different amount of growth at LNI 70, raised by the different amount of nitrogen supply under gravel culture, were supplied with different levels of nitrogen solution during the period of the middle growth stage (70-90 in LNI). The following results were obtained: 1. The lower the nitrogen concentration of the nutritional solution during the treatment, the less in the dry weight, the total activity of 32P in rice plants and the amount of oxygen consumed by roots, at the expiry of the treatment. 2. Under an identical nitrogen concentration during the treatment, the smaller the growth amount at LNI 70 was, the greater the decrease was found in the dry weight, total activity of 32P and the amount of oxygen consumed by roots, respectively. And the longer in the length of the treatment, the higher effect of growth retardation was obtained. 3. Judging from the amount of <32>P uptake and the oxygen consumed by roots, in the plants fed with 30 ppm of nitrogen before the treatment, conspicuous effects of the treatment on the plant growth appeared in 2 weeks after the starting time of the treatment, and the rice plants seemed to be able to recover from the growth retardation by the treatment in the case of 3 week-treatment. And also in the plants fed with 60 ppm of nitrogen before the treatment, the effect of the treatment was detected in 3 weeks after the starting time of the treatment and the rice plants seemed to be able to recover from the growth retardation even in 4 week-non-nitrogen treatment. 4. Compairing with the ratio of the growth amount of the plants fed with 0, 5 and 10 ppm of nitrogen during the treatment against that of control (which was supplied with 60 ppm of nitrogen before the treatment and 30 ppm during the treatment, abbr. 60-30 ppm), the indices of the growth amount of 60-0 ppm and 30-10 ppm showed nearly identical values, at 10 day nourishment with 30 ppm of nitrogen solution after 3 week-treatment. 5. Examining the effect of the nitrogen restriction treatment on the growth of rice plants, it is necessary to consider the following 3 factors; the growth amount at the starting time of the treatment, the nitrogen concentration of nutritional solution during the treatment and the length of the treatment period.

[学科分类] 农业科学（综合）