Genotypic Variation in Photosynthetic Traits, Grain Yield and Nitrogen Use Efficiency in Rice (Oryza sativa L.) Under Differential Nitrogen Levels

Nitrogen (N) is one of the yield limiting nutrients for rice. Unwarranted usage of N fertilizer to achieve higher crop returns is affecting environment and increasing the cost of cultivation. A field experiment was conducted under two differential N experimental plots (N-Low and N-Rec) to evaluate the effect of N on photosynthesis, grain yield and nitrogen use efficiency (NUE) of six rice genotypes belonging to three diverse groups. At N-Rec, Kolajoha3 exhibited highest mean SCMR value (43.2), flag leaf length (39.0 cm), flag leaf width (1.77 cm), flag leaf area (53.8 cm2 ), photosynthetic rate (19.50 µmol CO2 m-2 s-1),stomatal conductance (0.38 mol [H2 O] m-2 s-1),transpiration rate (10.72 mmol [H2 O] m-2 s-1). IC463254 recorded highest mean grain yield (621.5 g m-2), total dry matter (1302.5 g m-2), harvest index (47.7%), grain N uptake (84.4 kg ha-1) and nitrogen use efficiency (18.2). Significant reduction in growth, photosynthetic rate and yield of rice occurred under N-Low compared with N-Rec. In comparison N-Rec, Kolajoha3 exhibited least mean reduction in plant height (10.68%), photosynthetic rate (14.96%), productive tiller number (35.40%), grain yield (50.63%), straw yield (24.83%), total dry matter (36.03%), agronomic efficiency (14.6%) and NUE (26.21%) under N-Low, while IC463254 exhibited least mean reduction in SCMR value (14.11%) and flag leaf width (23.66%).