Physiological responses of high-yielding rice cultivars to elevated nitrogen levels

The nitrogen (N) requirement of rice cultivars may differ because of differences in growth duration and N dynamics in the soil. Variability in N utilization, content and uptake by grains affects the physiological aspects and yield. Therefore, a glasshouse experiment was conducted in Bangladesh to investigate the impact of cultivars and N content on growth dynamics, biomass partitioning, yield, and nitrogen-use efficiency (NUE). Ten high-yielding boro (dry season irrigated) rice cultivars viz. BRRI dhan28, BRRI dhan29, BRRI dhan47, BRRI dhan50, BRRI dhan59, BRRI dhan60, BRRI dhan61, Binadhan-8, Binadhan-10, and Binadhan-14, along with four N concentrations (0, 70, 140, and 210 mg kg(-1) in the soil) were used. The cultivar Binadhan-8 had a higher yield in all N treatments because of the highest total dry matter (TDM), effective tillers hill(-1), and grains panicle(-1). Growth, TDM, yield, and NUE were increased with fertilizer application up to N-140, after which declined with increasing N. The highest N content in grain and straw (3.047% and 1.737%) was shown by Binadhan-8. Significant relationships between N concentration and growth dynamics, biomass partitioning, N content, uptake and yield were observed. In addition, excess use of N decreased efficiency, because at a higher concentration of N, absorption exceeds utilization. Therefore, the study was useful in the screening of the most efficient cultivars, which could be used to enhance crop yield and reduce the use of N fertilizer.