Onion is an economically important cash crop in Ethiopia and the Amhara Region, which is widely produced under irrigation condition to meet year-round market demand. Despite its importance, however, onion production faces challenges such as low productivity due to a lack of improved varieties with extended shelf life, improper fertilization practices, suboptimal plant density. Studies were conducted in 2021–2023 in North Mecha (Koga), Bahir Dar Zuria (Woramit), and Fogera (Woreta) districts to assess farmers' knowledge and management practices, identify key supply chain constraints, and optimize nitrogen fertilizer rates and plant populations to enhance onion growth, yield, and quality. The study combined a field experiment and a survey. Field experiments were laid out in a factorial arrangement using a Randomized Complete Block Design (RCBD) with three replications. The survey result showed that onion production is dominated by adults households, but faces challenges of input shortages, high costs, and postharvest losses. Seven alternative marketing channels were identified, involving key actors such as farmers, local collectors, brokers, transporters, wholesalers, retailers, and consumers. The majority of the produce (66.15%) was sold to wholesalers. However, producers received only a small share of the final consumer price, while experiencing the highest average postharvest losses among all actors in the supply chain. Similarly, the experimental study indicate that onion growth and yield are significantly influenced by planting density, variety, and nitrogen fertilizer rate across growing location. Hybrid varieties (Russet and Jambar) consistently exhibited superior performance, achieving the highest bulb diameter, weight, harvest index, firmness, total yield, and marketable yield under the planting density of 666,666 plants ha 22 -1 across all locations. Russet and Jambar recorded the highest marketable yields of 28.54 t ha -1 and 26.61 t ha , respectively. Planting at higher densities (666,666 plants ha -1 ) with a spacing of 40cm x 20cm x 5cm between double rows, rows, and plants respectively resulted in the highest marketable yield (28.42 t ha -1 ). Moreover, the application of 82 kg ha -1 nitrogen fertilizer further enhanced growth and yield parameters, with Russet and Jambar achieving yields of 26.50 t ha -1 and 24.57 t ha -1 , respectively, across locations. The hybrid varieties (Russet and Jambar) and optimal nitrogen application rate (82 kg ha -1 ) also provided the highest net benefits. Postharvest quality was significantly influenced by packaging materials, nitrogen fertilizer, and variety. Proper handling allowed onions to be stored for up to one month without significant losses, regardless of the packaging materials used. Russet and Jambar varieties, when produced with optimum nitrogen fertilizer rate and stored on locally constructed shelves exhibited delayed sprouting, minimal decay, lower weight loss, and better firmness. In contrast, Bombay Red and Red Coach varieties showed higher storage losses. The study recommends for producers and traders in the study area, as well as similar to agro-ecologies adopt Russet and Jambar varieties, combined with higher planting densities and 82 kg ha -1 nitrogen fertilizer for improved onion. Storing bulbs on shelves until market conditions improved can contribute to a sustainable onion supply chain. Furthermore, the study found that pre-harvest treatments, such as toppling at 90% neck fall, improved postharvest storage. Onions of Jambar and Russet varieties were able to be stored for up to four weeks without significant loss. The study underscores the need for further exploration, particularly to evaluate various hybrid onion varieties at high plant density levels. The investigation of phosphorus fertilizer is also recommended for -1 future research, and since the study's limitation to a single season and location, further research is needed to test and to validate these findings across multiple locations and repeated years.