Effects of controlledrelease iodine fertilizers on iodine accumulation andsome physiological characteristics of lettuce

A greenhouse pot experiment was conducted to assess the effects of controlledrelease iodine fertilizers on the iodine accumulation and physiological response of lettuce in comparison with traditional iodine fertilizers. The plants were subjected to different iodine fertilizers containing two levels of iodine as iodate or iodide, 10 and 20 mg/kg soil. The results show that all the treatments with iodine applied significantly increase the iodine contents in leaves of lettuce. The leaf iodine contents developed from the controlledrelease potassium iodate and the controlledrelease potassium iodide are significantly enhanced by 46.60%-61.16% and 46.59%-58.53% in comparison with the corresponding traditional iodine fertilizers, respectively. The biomass amounts (fresh mass and dry mass of shoot and root) and leaf chlorophyll contents of lettuce grown with the controlledrelease iodine fertilizers are higher than those of the traditional iodine fertilizers. The growthpromoting function is also associated with the increases of vitamin C and activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) in lettuce leaves. Application of the controlledrelease iodine fertilizers results in the reduced NO-3-N content and diminished lipid peroxidation (MDA) content of lettuce leaves. Amount of iodine in leachate peaked with controlledrelease iodine fertilizers are higher than those of the traditional iodine fertilizers. The controlledrelease potassium iodate and the controlledrelease potassium iodide also significantly reduce the iodine leached rates by 45.99%-50.97% and 39.18%-46.29% compared to the traditional fertilizers, respectively. When iodine applied rate is 20 mg/kg soil, the leaf iodine content is significantly higher than that of the 10 mg/kg soil, while no significant differences are found in other indexes. Overall, the controlledrelease iodine fertilizers increase iodine accumulation in lettuce leaves, prevent iodine leaching and improve iodine use efficiency, and are proven to be the optimum for cultivating iodineenriched vegetables.