Abstract

Bombay Red’ is one of the most widely used onion cultivars in Ethiopia. Seed production of this cultivar is expanding among farmers. However, various constraints are reported for the low seed productivity of this cultivar, out of which inappropriate uses of bulb size and intra-row spacing are the most important ones. Therefore, a field experiment was conducted at Bati Futo watershed, Meskan Wereda, Southern Ethiopia under supplemental irrigation in 2012 to find out optimum bulb size and intra-row spacing for quality and economically feasible seed production of the cultivar. The crop was grown in factorial combinations of four different bulb sizes (3-4.0,4.1-5.0, 5.1-6.0 and 6.1-7.0 cm) and four intra-row spacings (10, 15, 20 and 25 cm) in a randomized complete block design with three replications. The results revealed that significantly highest value of days to 50% bolting (27 and 28 days), days to 50% flowering (75 and 81 days), days to 50% maturity (123 and 124 days), number of leaves per plant (37 and 36), biomass (130 and 146 g/plant), flower stalk height (84 and 74 cm), flower stalk diameter (1.62 and 1.75 cm), umbel diameter (5.52 and 5.82 cm), number of umbels per plant (11 and 10), number of umbels per plot (854 and 1016), 1000-seed weight (4.50 and 4.35 g) and seed germination percentage (92 and 91 %) were obtained from bulbs of 6.1 to 7 cm size and 25 cm intra-row spacing, respectively. However, the maximum (2.05 and 1.80) leaf area index was obtained at 6.1 to 7 cm bulb size and 20 cm spacing, respectively. The interaction effects of bulb size and intra-row spacing on number of seeds per umbel, weight of seeds per umbel, seed yield per plant and seed yield per hectare were significant. Significantly higher seed yield (920 to 995 kg/ha) was obtained at the larger bulb size (5.1 to 7 cm) grown at 20 and 25 cm spacing. The highest net field benefits of 245,678 Ethiopian Birr ha^-1 was obtained from a bulb of 5.1-6.0 cm sizes grown at 20 cm spacing. Hence, for quality and economically feasible seed yield of onion, the treatment combination of 5.1 to 6.0 cm bulb size and 20 cm spacing is recommended to the farmers at Bati Futo watershed.

Key words: Bulb size, intra-row spacing, onion seed production.