Effect of Sulfur on the Yield, Quality and Storability of Two Onion (Allium cepa L.) Cultivars

Effect of different amounts of sulfur fertilizer (0, 50, 100, 150, 200, 250 kg/ha) and 200 kg/ha of Thiobacillus inoculant on yield, quality and storability of two edible onion cultivars Red Rey and White Qom were investigated. The experiments were conducted at experimental field and laboratories of the Department of Horticulture, Seed and Plant Improvement Institute, Karaj, Iran in 2007-08 cropping seasons. A factorial arrangement in randomized complete block with four replications was employed. Effect of sulfur fertilizer on the yield and bulb mean weight was significant at the 5% level, and the highest yield and bulb mean weight was obtained at 200 kg/ha sulfur with Thiobacillus. The increase in yield and mean bulb weight was in accordance with the increase in above ground fresh weight. Furthermore, characteristics as diameter and height of the bulbs as well as the thickness of the bulb neck were affected by the sulfur treatments. Sulfur had positive effects on the total soluble solids (TSS), bulb dry matter (DM), bulb firmness and pyruvic acid of the bulbs as quality proporties. Increasing of Sulfur up to 150 kg/ha resulted in increase of TSS, DM, bulb firmness and pyruvic acid of the bulbs. Sulfur at 200 and 250 kg/ha levels resulted in decrease of TSS, DM, bulb firmness and pyruvic acid. However, the highest total soluble solids, bulb dry matter, bulb firmness and pyruvic acid resulted from application of 200 kg/ha with Thiobacillus. Sulfur affected weight loss (%) during the storage period and the increase of sulfur up to 200 kg/ha resulted in decrease in sprouted bulbs and weight loss. There was significant interaction between the levels of sulfur and onion cultivar. Yield and mean bulb weight, height of the bulbs, in White Qom was higher than Red Rey. Furthermore, the sharpest taste, and the lowest sprouted bulbs observed in the Red Rey cultivar. Therefore, application of 200 kg/ha of sulfur fertilizer with Thiobacillus had considerable effect on enhancement of yield and quality in white Qom and Red Rey onion cultivars.