Nitrogen % in both straw and grain, nitrogen uptake by straw and grain, total nitrogen uptake and physiological nitrogen use efficiency (PNUE) showed significant differences due to variable nutrient levels at maturity in traditional rice varieties. PNUE ranges from 40.58 to 49.88 (kg/kg N). Significantly higher PNUE without addition of nitrogen (Zero N) indicated the ability of utilization of the native nitrogen by traditional varieties. Traditional varieties produced 49.88 kg grain by the utilization of zero nitrogen treatment followed by 45.93 kg grain in cowdung (10 t/ha), while 40.58 kg grain by the application of 80 kg/ha nitrogen. The higher PNUE in zero nitrogen treatment confirmed the ability of producing similar yield level compared to added nitrogen treatment. Bashful chikon, might be important due to higher nitrogen content and Badiruzzman considered due to more straw nitrogen (0.71%). Barud also showed excellence with regards to PNUE and total nitrogen uptake. Leaf chlorophyll profile showed a very consistent level in all the varieties except Laichi. Soil plant analysis development (SPAD) value ranged from 34.06 to 41.69, while leaf nitrogen ranged from 2.99 to 3.49 %. SPAD value recorded over time showed four distinct patterns during 15 to 90 DAT.

A field study was conducted to understand nitrogen use efficiency of high yielding Japonica rice varieties under three levels of nitrogen fertilizer (90, 150 and 210 kg N ha -1 ) in Iksan, Korea. Two high yielding rice varieties, Boramchan and Deuraechan, and an control variety, Dongjin2, were grown in fine silty paddy. Nitrogen use efficiencies (NUE) were 83.3, 56.3, and 41.2 in 90, 150, and 210 Nitrogen is the most critical input that limits rice productivity (Mae, 1997). The required amount of nitrogen depends on soil type, variety, climate, method of application and type of fertilizer. However, supply of proper amount of nitrogen based on the physiological requirement is the key factor. Through proper nitrogen management, one kg of nitrogen accumulation can produce 50 kg of grain under irrigated conditions (Yoshida, 1981). However, acquisition of applied nitrogen by the rice crop is typically less than 40% in farmer's fields (Cassman et al., 1993). Further increase of yield from the existing cultivars is possible by increasing nitrogen use efficiency (NUE).For crops, NUE can be defined as grain yield per unit nitrogen supply (Moll et al., 1982). NUE is understood by the combination of the nitrogen uptake efficiency (NUpE) and nitrogen utilization efficiency (NUtE). Nitrogen use efficiency (NUE) largely depends on nutrient balance, water availability, light intensity, disease pressures and cultivated variety. Nitrogen efficient genotype is considered in two different terms: the ability to convert high nitrogen input into yield comparatively better than other genotypes or the ability to realize an above average yield at suboptimal nitrogen level. Rice genotypes showed different nitrogen uptake, nitrogen translocation efficiency, and also NUE (Broadbent et al., 1987; Koh, 2007, Singh et al., 1998). In some researches, increasing NUpE is focused as the strategy to increase NUE with high grain yield (Cassman et al., 1993;Rauna and and Johnson, 1999;Feng et al., 2011).Grain yield of rice is the final product of the combination of number of panicles per unit area, spikelet density, percentage of filled spikelets and grain weight. The primary yield determinant of yield in rice is the number of spikelets per unit land (Gravoid and Helms, 1992). For achieving higher yield in rice, the sink size should be increased by increasing panicle size or number or either. The cultivars having large panicles may the best option but the adequate numbers of panicles need to be maintained properly in terms of sink-source balance (Kim et al., 1993). Therefore, this study has undertaken to evaluate the morpho-physiological response of high yielding Japonica rice varieties under variable nitrogen levels. The experiment was laid out in a split plot design with three replications, where nitrogen levels were in the main plot and rice varieties were in subplots. The subplot size was 28 m × 2.6 m. The nitrogen levels were 90, 150, and 210 kg N ha -1 and three Japonica rice varieties were Boramchan, Deuraechan and Dongjin...