Nitrogen response of two high yielding rice varieties as influenced by nitrogen levels and growing seasons

Proper nitrogen (N) management of high yielding rice varieties is crucial for obtaining their potential yield benefit. In this study, we compared the effect of different N rates on rice growth, yield, and N use efficiency of two high yielding rice varieties (BRRI dhan58 and BRRI dhan75) in a Boro (dry season)-fallow-T. Aman (wet season) cropping pattern. The N rates were: 0, 25, 50, 75, 100, 125, 150 and 175 kg ha−1 which were assigned in randomized complete block design with three replications. In Boro season, BRRI dhan58 showed higher response to applied N compared to BRRI dhan75 in T. Aman season. The calculated optimum N dose to maximize yield of BRRI dhan58 and BRRI dhan75 were 142 kg ha−1 and 82 kg ha−1, respectively. The agronomic N use efficiency and fertilizer N recovery efficiency were comparatively higher in BRRI dhan58 grown in Boro season than BRRI dhan75 grown in T. Aman season, while in both seasons, the N use efficiencies decreased with increased N rates. This study results suggest that variety-specific N fertilization with respect to growing season is the best N management practice to maximize rice yield avoiding the excess use of N fertilizer.