Growth and yield response of irrigated rice to nitrogen fertilizer rates in Southern Bangladesh

Nitrogen (N) fertilizer application is crucial for rice cultivation, however both low and excessive applications decreased productivity. A field experiment was carried out to determine the optimum N fertilizer dosage for improved crop performance by utilizing RCBD design with eight treatments (recommended-124, recommended but no nitrogen, 50, 100, 150, 180, soil test based-88 kg ha-1 and untreated control) and three replications at Bangladesh Rice Research Institute, Sonagazi, Feni. The growth, yield components, and productivity were significantly influenced by N fertilization with increasing N rates up to 180 kg N ha-1, particularly in plant height, tiller and panicle number, panicle length, filled and unfilled grain number, and grain yield. Tiller and panicle numbers increased markedly with N application, underscoring nitrogen’s role in vegetative growth and development and sink capacity. Grain filling positively influenced by N rates, attributed to enhance photosynthesis and assimilate partitioning. Conversely, spikelet sterility was markedly higher in low or zero-N treatments, indicating N deficiency-induced reproductive failure. Days to flowering and maturity were slightly delayed at higher N rates. The thousand grain weight remained relatively unaffected by N levels, highlighting grain yields dependency on increased grain number rather than size. Regression analysis revealed a strong positive correlation (0.908) between N rate and grain yield at 150 kg N ha-1 and 180 kg N ha-1. Both straw and total biomass yields mirrored grain yield patterns, and higher harvest index values at elevated N (150 and 180 kg N ha-1) rates confirmed effective conversion of biomass to grain and might be used for higher productivity.