Biofortification of Carrot (Daucus carota L.) with Iodine and Selenium in a Field Experiment

The low content of iodine (I) and selenium (Se) forms available to plants in soil is one of the main causes of their insufficient transfer in the soil-plant-consumer system. Their deficiency occurs in food in the majority of human and farm animal populations around the world. Both elements are classified as beneficial elements. However, plant response to simultaneous fertilization with I and Se has not been investigated in depth. The study (conducted in 2012–2014) included soil fertilization of carrot cv. “Kazan F(1)” in the following combinations: (1) Control; (2) KI; (3) KIO(3); (4) Na(2)SeO(4); (5) Na(2)SeO(3); (6) KI+Na(2)SeO(4); (7) KIO(3)+Na(2)SeO(4); (8) KI+Na(2)SeO(3); (9) KIO(3)+Na(2)SeO(3). I and Se were applied twice: before sowing and as top-dressing in a total dose of 5 kg I⋅ha(-1) and 1 kg Se⋅ha(-1). No negative effects of I and Se fertilization were noted with respect to carrot yield. Higher accumulation and the uptake by leaves and storage roots of I and Se were obtained after the application of KI than KIO(3), as well as of Na(2)SeO(4) than Na(2)SeO(3), respectively. Transfer factor values for leaves and roots were about a dozen times higher for Se than for I. Selenomethionine content in carrot was higher after fertilization with Na(2)SeO(4) than with Na(2)SeO(3). However, it was the application of Na(2)SeO(3), KI+Na(2)SeO(3) and KIO(3)+Na(2)SeO(3) that resulted in greater evenness within the years and a higher share of Se from selenomethionine in total Se in carrot plants. Consumption of 100 g f.w. of carrots fertilized with KI+Na(2)SeO(3) and KIO(3)+Na(2)SeO(3) can supply approximately or slightly exceed 100% of the Recommended Daily Allowance for I and Se. Moreover, the molar ratio of I and Se content in carrot fertilized with KI+Na(2)SeO(3) and KIO(3)+Na(2)SeO(3) was the best among the research plots.