Abstract
The authors examined the effects of nitrogen deficiency in the middle growth period (69∼92in leaf-number index, 43∼20 days before heading) on the physiological activity of roots of rice plants grown under water cultures as well as soil cultures. The results obtained can be summarized as follows. 1. In water cultures the physiological activity of roots increases with an increasing amount of aerated air and a decreasing amount of S04 in the medium. 2. In case of the nitrogen supply being completely interrupted in water cultures, the physiological activity of roots considelably goes down on account of the medium being changed for the worse. However, in case of the nitrogen supply being reduced to one fifth or on tenth of an ordinary level, the physiological activity of roots scarcely goes down. 3. In soil cultures (under field conditions) nitrogen supplply have also been controlled by using nitrate nitrogen and by drying up soil, but the depression of physiological root activity can hardly be recognized. The root activity seems to be influenced by the kinds of soil, facility of drainage and methods of watering. 4. Accordingly, the depression of physiological root-activity by nitrogen deficiency in the middle growth period can hardy be recognized under actual field conditions, because the nitrogen supply is completely interrupted only in very few cases and furthermore the soil in paddy field is commonly aerated by the practise of drying up soil in the middle growth period. 5. Sometimes it can clearly be recognized the phosphats and potash, not to speak of nitrogen, are absorbed the more by the plants in the period after the nitrogen supply is temporarily interrupted, as reported by the other authors.
