Nitrogen Effects on Growth Responses and Carbohydrate Concentrations in Source and Sink Tissues of Two Rice Cultivars

Two rice cultivars (Oryza sativa L.), Hwa-seongbyeo of Japonica type and Taebackbyeo of Indica/Japonica type, were cultivated with hydroponic culture to examine nitrogen effects on the growth responses, contents and utilizations of carbohydrates, and the ripening velocity of grains with three different N levels. Plant height and tiller number were clearly increased to 80 ppm N level compared to 40 ppm N level and then they were slightly decreased in N level of 120 ppm. Higher dry weights were appeared with 80 ppm N level than did with other N levels, showing statistically differences in both cultivars and N levels, while dry weight of roots was heavier with decreasing the N levels. Therefore, T/R ratios were not significantly different among N levels, although there was statistically differences between rice cultivars. After the flowering stage, higher water-soluble carbohydrate (WSC) and water-insoluble carbohydrate (WISC) were contained in stem compared with other parts, showing that WISC of sheath and stem, unlike WSC, was significantly different among N levels. Starch of grain, WISC, was remarkedly increased from 3.0% at just after the flowering to 52.0% and 75.0% at 15 and 30 day after the flowering, respectively, showing that lower N application had faster accumulation of starch in rice grains. N would affect the contents of carbohydrates of each tissue, and starch accumulation in rice grains.