International Journal of Plant & Soil Science

Efficient nitrogen (N) management is critical for optimizing rice productivity, especially in nutrient-deficient soils of sub-Saharan Africa. A split-plot design with three replications was used, with rice variety as the main plot and nitrogen rate as the subplot. This study evaluated the response of five upland rice genotypes (Nerica 1, CSR36, Komboka, 17KH090014B, and AT058 to seven nitrogen application rates (0, 17, 34, 51, 67.5, 83.4 and 101 kg N ha^-1) in two agro-ecological zones Bura and Taveta across two cropping seasons.The Nitrogen (N) treatments were applied as topdressing in 3 equal splits, at 15 Days after Transplanting (DAT), peak tillering (30 DAT) and panicle initiation stage (45 DAT). Data collected was subjected to ANOVA using Statistical Tool for Agricultural Research and means were separated using the Turkey's Test Honest Significant Difference HSD test. All statistical analysis was performed at alpha=0.05. Nitrogen significantly (P < 0.05) enhanced vegetative and yield traits up to an optimal rate of 67.5 kg N ha⁻¹, beyond which gains were minimal. At this level, plant height, tiller number, leaf length, panicle length, and fertile grains per panicle increased by 12%, 15%, 9%, 8%, and 47%, respectively, over unfertilized plots. Genotype 17KH090014B exhibited superior performance, producing the highest total (142.22) and fertile (99.28) grains per panicle, longest panicles (20.65 cm), and most leaves per plant, while Nerica 1 was tallest (60.63 cm) and Komboka had the most tillers (25.2). The variety–nitrogen interaction peaked with 17KH090014B at 83.4 kg N ha⁻¹, yielding 143.8 grains per panicle. Findings suggest that 67.5 kg N ha⁻¹ for 17KH090014B during the long rains could be a variety- and site-specific recommendation for upland rice in Taita Taveta County, provided further validation is conducted using broader sampling across the region.