Abstract
Investigations on the nitrogen metabolism was regarded as of great importance among the matter concerning plant nutrition. Especially in Japan, rice plants are raised at paddy field under waterlodged condition, thereby rice-plants preferentially absorb ammonia-nitrogen than nitrate form. We have attempted to explain the mechanism of nitrogen metabolism through qualitative and quantitative investigations of assimilation process on absorbed ammounia-nitrogen by roots. Riceplants (Norin No.18) were cultivated in Wagner pots. For nitrogenous fertilizer, sulphate of ammonia was given as basie application and top dressing at different stage, and then the growth and yield of rice crops were carefully examined. Among all plots, the best result was obtained at one of basic application and in addition top dressing at primordial stage, namely about three weeks before heading. Starch, reducing and non-reducing sugars were estimated about whole samples taken once a week. From the standpoint of carbohydrate accumulation, shortly after transplanting stored carbohydrates were exhaused. Then the content of carbohydrate generally arises, but at the younger stage nitrogen assimilation predominates than carbon assimilation. After primordial stage the photosynthesis exceeds the nitrogen assimilation. Dressing of nitrogen rapidly reduces the content of carbohydrate in the rice plant, and after some interval again rearises to the degree far higher than before. Especially dressing of primordial stage has strongest effect of promotion of carbohydrate content. This causes an effective increasing yield of crop.
