Effect of Increase of the Water Level on the Uptake and Distribution Pattern of Nitrogen in the Main Stem and Tillers of Floating Rice

Changes in the total nitrogen (N) and heavy nitrogen (15N) contents in the main stem and tillers of floating rice varieties grown at different water levels were investigated. The total N was predominantly accumulated in the main stem and the primary tillers originating from the lower nodes of the stem , regardless of the rate of increase of the water level, while that in the primary tillers on the upper nodes and in the secondary tillers decreased with the increase of the water level. The amounts of 15N in the primary tillers on the higher nodes and in the secondary tillers increased under standard submerged conditions and under deep water conditions, while those in all the tillers were translocated to the main stem when the water level was high (8 cm increase per day). These results suggest that under deep water conditions in floating rice the sink-source activity of N in the organs varies to preserve adequate physiological conditions.