Onion is a key vegetable crop in Ethiopia, playing a significant role in household diets and serving as a vital income source for farmers. Despite its importance, onion productivity remains low, largely due to inadequate soil fertility and water stress. This study was conducted during the 2021/2022 cropping season at Melkassa, East Shewa, to evaluate the effects of varying NPS fertilizer rates and irrigation frequencies on onion yield and associated agronomic traits. The experiment employed a split-plot arrangement within a randomized complete block design (RCBD) with three replications. Treatments included five NPS fertilizer levels (0, 100, 150, 200, and 250 kg ha?¹) and three irrigation schedules: I? (3-4-5-6-days intervals), I? (5-6-7-8-days intervals), and I? (7-8-9-10-days intervals) across crop growth stages. Results indicated that both NPS fertilizer and irrigation frequency significantly (P<0.05) affected most yield and growth parameters. The highest marketable bulb yield (31.61 t ha?¹) was obtained from the 250 kg ha?¹ NPS application under the most frequent irrigation (I?), while the lowest yield (9.33 t ha?¹) was recorded under no fertilizer and the least frequent irrigation (I?). Therefore, applying 250 kg ha?¹ NPS fertilizer with frequent irrigation (I?) is recommended to enhance onion productivity in similar agro-ecological settings.

Keywords: Crop water requirement; Harvest index; Blended fertilizer; Marketable bulb yield; Total soluble solid