Effect of irrigation regime and plant density on quantitative and qualitative traits of onion (Allium cepa L.) in Isfahan

In order to study the effects of irrigation regimes and plant spacing on bulb yield of two onion (Allium cepa L.) genotypes, an experiment was conducted at Kabootar Abad Research Station of Isfahan during two growing seasons (2005 and 2006). The experiment design was split-factorial with a randomized complete block arrangement with four replications. Main plots included three irrigation regimes (irrigation after T1= 503 mm, T2= 703 mm and T3= 903 mm evaporation from class A pan). Sub-plots formed from factorial combination of two spring onion genotypes (Yellow Sweet Spanish and Dorcheh-Isfahan) with three plant spacing in rows (5, 7.5 and 10 cm). The results showed that total yield, marketable yield, bulb diameter and bulb height decreased as irrigation frequency increased. The highest total yield (6.867 kg/m2) and marketable yield (5.761 kg/m2) were produced in T1 treatment. Regarding total yield, the response of genotypes to increasing irrigation frequency was different. The Yellow Sweet Spanish genotype tolerated water deficit more than Dorcheh. Total yield, marketable yield and bulb height in Yellow Sweet Spanish genotype were significantly greater than Dorcheh, but diameter of bulb neck, dry matter and total soluble solids in Dorcheh were significantly greater than Yellow Sweet Spanish. Among the plant spacings, the 10 cm spacing had the lowest total and marketable yield and there were no significant differences between 5 and 7.5 cm spacing. But bulb size (height and diameter) increased as plant spacing increased.