Impact of Blended Mineral NPSB and Urea Fertilizer Rates on the Growth, Yield, and Yield Components of Onion (Allium cepa L.) in Mersa, Northeastern Ethiopia

Onion (Allium cepa L.) is one of the most significant vegetable crops cultivated extensively in Ethiopia, especially in the northeastern region. However, due to environmental stresses, its productivity is lower than the world average. The lack of improved varieties, postharvest losses, diseases and pests, low soil fertility, and inadequate plant nutrients are key constraints limiting its productivity. An experiment was conducted at the Mersa College of Agriculture Research Station, Woldia University, to optimize the rates of blended NPSB and urea fertilizer for improving onion crop growth, yield, and quality. The experiment involved a factorial combination of four NPSB rates (0, 100, 200, and 300 kg/ha¹) and four urea rates (0, 100, 150, and 200 kg/ha), arranged in a Randomized Complete Block Design with three replications. The analysis of variance indicated that the interaction between blended NPSB and urea fertilizer significantly affected the days to 70% physiological maturity, plant height, leaf length, mean bulb weight, and both marketable and total bulb yields. Leaf and bulb diameter, neck thickness, dry weight, cumulative weight loss, bulb sprouting, and rotting percentage were significantly influenced by the main effects of blended NPSB and urea fertilizer rates. The highest total bulb yield (41.4 t/ha ¹) and marketable bulb yield (40.58 t/ha), along with the maximum net benefit (1,812,053 ETB/ha) at an acceptable MRR (7469%), were achieved with the combination of 200 kg ha⁻¹ blended NPSB and 150 kg/ha urea. Therefore, to maximize onion productivity in the study area and similar agroecologies, it is essential to apply economically feasible rates of 200 kg/ha blended NPSB combined with 150 kg/ha urea. However, the experiment should be repeated over different seasons and locations to make a decisive recommendation.