AbstractA field experiment was conducted at the Livestock Research Centre of G. B. Pant University of Agriculture and Technology, Pantnagar, India during the wet season (June—October) of 1980 with the objectives of characterizing the seasonal changes inin vivonitrate reductase activity (NRA) and N contents of upland rice cultivars grown under rainfed condition at low (0 kg N/ha) and optimum (80 kg N/ha) N fertility.In vivoNRA increased initially up to panicle initiation stage (50 days after sowing) and declined, thereafter, until 90 days. Leaf NO3‐N content paralleled within vivoNRA throughout crop season. Total N content of leaves and stem declined with advance in crop age, whereas panicle N content increased with the crop development. Optimum N fertility (80 kg N/ha) always resulted in higher NRA, NO−3and total N contents of rice p