Abstract
Nitrogen (N) is the most important yield-limiting plant nutrient. Despite various measures available for improvement of N management, nitrogen use efficiency (NUE) is still very low in rice (Oryza sativaL.), particularly under rainfed conditions. A field experiment was conducted at the Regional Agricultural Research Station, Banke, Nepal, during the rainy seasons of 2017 and 2018 to study the effects of nitrogen application method on NUE and grain yields across different varieties. The field experiment was laid out in a split-plot design, consisting of three rice varieties-Arize 6444, Radha-4, andSukkha Dhan-3-as the main plots and five fertilizer treatments in sub-plots, and replicated thrice. The five fertilizer treatments included control (0 kg N ha(-1)), broadcast prilled urea at 78 kg N ha(-1)and 100 kg N ha(-1), and deep placement of prilled urea and briquetted urea at 78 kg N ha(-1). Both rice variety and fertilizer treatment had a significant (p < 0.05) effect on grain yield. The hybrid variety (Arize 6444) increased grain yield by 23% compared toSukkha Dhan-3(4.9 Mg ha(-1)). Deep-placed briquetted urea increased grain yield by 21-23% (6.7 Mg ha(-1)) compared to broadcast and deep-placed prilled urea. A higher grain yield for briquetted urea positively correlated (r = 0.43) with the number of tillers per hill. Deep-placed briquetted urea increased NUE (apparent N recovery, agronomic NUE, partial factor productivity of N, and physiological efficiency by 44%, 40%, 34%, and 3%, respectively), while reducing ammonia volatilization by 57% compared to the current recommended rate of broadcast prilled urea. Our results confirm that deep placement of briquetted urea significantly increases grain yields and NUE of rainfed rice.