Different nitrogen levels are recommended in rice production systems but the judicious use of nitrogenous fertilizer is of supreme importance for economically viable and environmentally safe production. A field experiment was conducted from June to November, 2017 in Agronomy Research Block of Agriculture and Forestry University (AFU), Rampur, Chitwan to study the effect of different N levels on nitrogen uptake and nitrogen use efficiencies of improved and hybrid rice varieties. The experiment was laid out in split plot design with four replications. Three varieties with two improved (Sabitri and Hardinath-1) and a hybrid (Arize Tej Gold) were used as main plot factor. Similarly, five N levels (0, 40, 80, 120 and 160 Kg N ha-1) were used as sub-plot factor. Results revealed the highest grain, straw and total nitrogen uptake at 160 Kg N ha-1 which was significantly higher than any other doses and control. Partial Factor Productivity of Nitrogen (PFPN) of Arize Tej Gold hybrid was significantly higher (42.67 Kg grain Kg-1 N) than both Sabitri and Hardinath-1. In general, with significantly higher grain, straw and total nitrogen uptake, higher PFPN, hybrid rice showed more efficiency in nitrogen use so, the Arize Tej Hybrid can be considered as better varietal choice for increased profitability of the rice production system. Different indices of Nitrogen Use Efficiencies (NUE) showed decrease in efficiencies with the increasing levels of N application as found in the experiment.
Katuwal et al. (2021) studied this question.