Abstract
This study was carried out to determine whether or not the reduction of seed yield due to the high level of nitrogen results only from the effect of lodging. The levels of nitrogen studied were 0 (0N), 1 (IN, ) 2 (2N) and 4kg N/a (4N) and the latter two levels were taken for high levels of nitrogen here. In relation to the lodging, treatments consisted of 1) the lodged plot in which the plant was left lodging naturally by rain, wind etc. and 2) the prevented plot in which the plant was supported mechanically by means of bamboo frames. In both lodged and prevented plots, nitrogen application increased the forage weight, but the difference among levels of nitrogen was not found in the prevented plots whereas a marked difference in the lodged plots, showing an increase in forage weight with more nitrogen. The lodging in plots without nitrogen was less and occurred later than in plots with nitrogen, and among those it was less and not severe in plots 1N compared with those having higher levels of nitrogen application. Higher number of ears was produced in the prevented plot than in the lodged one. But the change of number of ears due to the level of nitrogen differed between Waseaoba and Yamaaoba and between lodged and prevented plots, that is, in Yamaaoba the maximum number of ears came out by 1N in both lodged and prevented plots, but in Waseaoba it came out by 1N in the lodged plot and by 2N in the prevented plot. Consequently, the difference in number of ears between varieties become greater in high levels of nitrogen. Higher seed weight per ear was also produced in the prevented plot than in the lodged one in all levels of nitrogen in both varieties, but the difference was observed between varieties in response to the nitrogen application. Seed yield was remarkably higher in the prevented plot than in the lodged one irrespective of varieties and levels of nitrogen. The effect of prevention of lodging was greater in high levels of nitrogen. The decrease of seed yield in the lodged plot was greater with more nitrogen, but the seed yield in prevented plot was also significantly decreased due to high levels of nitrogen as in lodged one. Consequently, it was recognized that the decrease in seed yield due to high levels of nitrogen application resulted not only from the lodging but also from other physiological reactions in plants.
