水稲収量の成立原理とその応用に関する作物学的研究 : 第116報 生育抑制効果に及ぼす窒素制限開始時の生育量と無窒素処理期間の影響

抄録

According to the authors previous studies, it was estimated that the effects of nitrogen depletion treatment at the middle stage of growth (70-90 in leaf number index) on the growth control varied with the amount of dry matter at the starting time of that treatment and with the length of treatment period. Therefore, raising rice plants with different amount of dry matter at the starting time of that treatment and varying the length of treatment period under gravel culture, the authors tried to clarify the above mentioned effects. The following are the results obtined in this study. 1. The plant with larger amount of dry matter at the starting time of that treatment gave less effect on the growth control than the plant with smaller amount of dry matter, even though the nitrogen depletion treatment was practised at the same growth stage for the same period. If the amount of dry matter at the starting time of that treatment was the same, the effect of 4 week-treatment was severer than that of 3 week-treatment. 2. When the dry matter of rice plants was lower than 100g/m² at the starting time of that treatment and the treatment was carried out for 4 weeks, the retardation of the plant growth by that treatment could not be recovered in spite of the nitrogen being fully supplied after that treatment, and the rice plant suffered from root-rot and then died away. However, in the case of the amount of dry matter being more than 300g/m² at the starting time of treatment, only little control effect on the plant growth was observed, even if 4 week-treatment was conducted. 3. It was supposed that there exsisted an optimum growth amount at the starting time of nitrogen restriction treatment and its corresponding optimum length of treatment period; so far as the present experiment was concerned, for example, the optimum growth amount at the starting time of the treatment appeared to be 200-300g/m² in the dry matter of rice plants (800-1000 in the number of tillers per square meter and 6-9 g/m² in the absorbed amount of nitrogen) and its corresponding optimum length of treatment period seemed to be 4 weeks. 4. From the results above mentioned, it will be deduced that the effect of nitrogen depletion treatment on growth control was difinitely governed by both the growth amount at the starting time of that treatment (which was mainly proportional to the amount of nitrogen absorbed by that time) and the length of treatment period.