Abstract
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 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.
Highlights
For the last few decades selenium (Se) has been considered as a beneficial element for plants – its indispensability for plants has not been proved
There are known reports indicating its positive influence on higher plants (Lehr et al, 1958; Borst-Pauwels, 1961) as well as those underlining the lack of clear understanding and explanation of physiological role of I (Kabata-Pendias, 2011)
It is significant that I content in a single portion of carrot fertilized with KIO3 together with Se every year would supply less than 100% of Recommended Daily Allowance for I (RDA-I)
Summary
For the last few decades selenium (Se) has been considered as a beneficial element for plants – its indispensability for plants has not been proved. The classification of iodine (I) into the group of beneficial elements for plants is not as unanimous as of selenium. Differences in iodine classification as a beneficial element result, among others, from the great difficulty in its determination – in our opinion, even greater than in the case of selenium. Another issue is diverse response of individual plant species to iodine application. There are, strong indications on positive influence of iodine on nitrogen use efficiency by plants (Blasco et al, 2012; Smolenand Sady, 2012) or the improvement of tomato fruits (Kiferle et al, 2013; Smolenet al., 2015)
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