抄録
Some relationships between the physiological and morphological characteristics of aerial parts in rice plants differing in plant type and other genetic characters, and root systems and root activities were presented in the previous papers (I to IV). In this study, a single variety, Nihonbare was used in order to find out effects of nitrogen level and placing position of the fertilizer on the chracteristics of root and aerial parts.The results obtained could be summarized as follows, (1) It was found that development and elongation of new roots were greatly retarded immediately after transplanting, when a higher level of nitrogen was applied as a basal-ferti-lizer. Therefore, a special caution should be paid to accelerate new root development through application of the optimum nitrogen amounts. (2) An excessive tillering of rice plants was observed at the stage of the maximum number of tillers, when a greater amount of nitrogen was applied as a basal-dressed fertilizer.This tendency was more pronounced as th amount of the upper roots was greater and the root activities were more active. However, the activities after this stage suddenly decreased, resulting in production of numerous invalid tillers. (3) On the other hand, the high root activity was maintained throughout the growth period, when the optimum amount of nitrogen as a basal-fertilizer was applied to deep-layer or to all the soil layers. As a results, a higher percentage of valid tillers was obtained in this case. (4) When the proper lelvel of nitrogen as a basal-feritilzer was applied to deep-layer and the whole layers, the activities of the total roots especially the lower nodal ones were active at the heading and ripening stages as compared with the activites in case of nitrogen, application to surface layer soil. The higher the lower-nodal root activity, the more chlorophyll was contained in the leaf and the slower destruction of chlorophyll in the leaf blade was taken place. It seemed very true that the higher yield was directly attributed to these relationships in case of nitrogen application to either deep-layer or the whole soil layers.
