| Summary: | 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. Plant response to simultaneous fertilization with I and Se has not been investigated in depth. Neither I nor Se is essential for higher plants but can be considered as a beneficial element. The study (conducted in 2012–2014) included soil fertilization of carrot cv. Kazan F1 in the following combinations: 1. Control; 2. KI; 3. KIO3; 4. Na2SeO4; 5. Na2SeO3; 6. KI+Na2SeO4; 7. KIO3+Na2SeO4; 8. KI+Na2SeO3; 9. KIO3+Na2SeO3. 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 KIO3, as well as of Na2SeO4 than Na2SeO3, 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 Na2SeO4 than with Na2SeO3. However, it was the application of Na2SeO3, KI+Na2SeO3 and KIO3+Na2SeO3 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+Na2SeO3 and KIO3+Na2SeO3 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+Na2SeO3 and KIO3+Na2SeO3 was the best among the research plots.
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