Effect of Plant Density and Planting Arrangement on Yield, Bulb Size and Storage-Life of Two Onion (‌Allium cepa L.) Cultivars

To study the effect of plant density and planting arrangement on yield and bulb size of two onion cultivars, a filed experiment was carried out as split factorial arrangement in randomized complete block design with three replications in the research field of Seed and Plant Improvement Institute, Karaj, Iran, in 2018-2019. Two onion cultivars, Morvarid and Zargan, were assigned to main plots, and inter row spacing of 10, 15, 20 cm and intra row spacing of 5, 7.5, 10, 12.5 cm as factorial were randomized in sub plots. Cv. Morvarid and cv. Zargan had the highest marketable yield in 15 × 7.5 and 15 × 10 cm planting arrangements (88.8 and 66.7 plant m-2, respectively) with 73.7 and 67.6 t ha-1, respectively. In cv. Morvarid and cv.Zargan, with decreasing the plant density, the proportion of small bulbs decreased from 38.31 to 6.57% and from 64.12 to 7.77%, respectively. In cv. Morvarid, with decreasing the plant density, large bulbs, doubles and thick neck bulbs increased from 3.19 to 19.85% and from 7.92 to 29.41%, respectively. In cv. Zargan, with decreasing the plant density to 66.7 plant m-2 (15 × 10 cm), the proportion of medium size bulbs increased from 35.87 to 80.15%. During the storage period, cv. Morvarid had lower percentage of bulb sprouting and decay than cv. Zargan in all planting arrangements. The results of this research showed that in cv. Morvarid and cv. Zargan, planting arrangements of 15 × 7.5 cm and 15 × 10 cm, respectively, could be recommended to onion producers, because less seedlings are required for transplantation when compared with higher plant densities.