Master's Thesis from the year 2008 in the subject Agrarian Studies, grade: 3.17, University of Hawassa (Awassa College of Agriculture), course: Horticulture, language: English, abstract: Plant density and bulb size trial was conducted at Ziway in order to identify the optimum agronomic management practices, which contribute to maximized seed production in onion crop both in terms of quantity and quality. The experiment was laid down in split plot design with three replications, keeping plant density as main plot factor and bulb size as sub plot factor. The effects were studied by collecting data on bulb sprouting and plant performance, yield components, seed yield and seed quality parameters. Analyses of variance, mean comparison using least significant difference, correlation analysis were made using SAS computer software. Plant density significantly influenced bulb sprouting, umbel size, seed yield per 100m2and germination percentage. The largest umbel size (4.9cm) was obtained from low plant density; where as the smallest (4.4cm) from high plant density. Maximum seed yield per 100m2(1,163,446 seeds) was collected from high density while low density yielded only 416,240 seeds per 100m2. However the quality of seed in terms of germination was highest for seeds obtained from low density. The influence of bulb size was significant on plant height, number of flower stalks per plant, number seeded florets per umbel, seed per plant, seed per 100m2, seed yield (qt/ha) thousand seed weight. Plants grown from large bulbs produced plants with best height (72.3cm), highest number of flower stalks (8.5), seeded florets per umbel (368.7), seed per plant (1,539), seeds per 100m2(994,434) and seed yield in qt/ha (10.42). Seeds with best thousand seed weight (4.2g) were obtained from medium bulbs and small bulbs performed least in all aspects. Correlation analysis was made to study the relationship among plant growth, yield component, seed yield and quality parameters and their respective influence on yield and yield quality. Positive correlation existed between plant height and umbel size with seeded florets per umbel; flower stalk per plant, plant height, umbel size, seeded florets per umbel and number of seeds per floret with seed yield per plant, which was highly correlated with seed yield (qt/ha). However, further studies ought to be conducted in order to understand clearly, why bulb size and plant density interaction effect was insignificant Key words: Plant density, bulb size, bulb sprouting, plant performance, seed yield and seed quality