Received: 10th April, 2023; Accepted: 23rd May, 2023

Abstract

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%).