Abstract
The strong sorption of iodine in soils is a major factor that limits its uptake by plants. The aim of this study was to evaluate the influence of Humistar (a concentrate of exogenous humic acids 12 % w/w and fulvic acids 3 % w/w; abbreviated: HU) applied with KI or KIO3 on the efficiency of iodine biofortification, yield and the accumulation of undesirable compounds in spinach. Methods of iodine application with or without HU were tested in two pot experiments and a hydroponic study with spinach cultivation. The spinach biomass and the content of iodine, soluble oxalates, Cd and Pb in leaves were determined. The physicochemical properties and chemical composition of the soil and media were analysed. No negative influence of iodine and HU on spinach yield was observed. Fertigation with iodine resulted in a higher efficiency of iodine biofortification than its application pre-sowing (particularly for KIO3), with no increase in the Cd and Pb content in spinach plants compared to the control. The improvement of iodine uptake and root-to-leaf transfer (represented by higher transfer factor values) in spinach can be obtained by the application of HU via plant fertigation with IO3 −. The level of soluble oxalates in spinach grown in the pot experiments was not affected.
Highlights
Iodine is a micronutrient that is essential for the proper functioning of human and animal organisms, in the prenatal period as well as during the initial years of life (Walker et al 2007; Charlton et al 2010; MelseBoonstra and Jaiswal 2010; Guyot et al 2011)
Fertigation with iodine resulted in a higher efficiency of iodine biofortification than its application pre-sowing, with no increase in the Cd and Pb content in spinach plants compared to the control
No significant influence of HU and iodine application was observed on the mean weight of the spinach leaves in 2009 and 2010 (Fig. 1a and b)
Summary
Iodine is a micronutrient that is essential for the proper functioning of human and animal organisms, in the prenatal period as well as during the initial years of life (Walker et al 2007; Charlton et al 2010; MelseBoonstra and Jaiswal 2010; Guyot et al 2011). Iodine deficiency disorder (IDD) is a term that describes the entire spectrum of dysfunctions related to the inadequate supply of this micronutrient in the diet (Delange 1998; White and Broadley 2009; Winger et al 2008). The iodine biofortification of plants is proposed as an alternative way to introduce iodine into food and can be an efficient method of IDD prevention. Iodine is not an essential nutrient for plants, prior to the implementation of biofortification rules into agricultural practice, optimal agrotechnical methods for its application need to be developed. Iodine undergoes strong sorption with soil organic matter or mineral fractions. This process occurs from 2 h (Hakimi 1996) to a few days (Muramatsu et al 1990; Kashparov et al 2005) after iodine introduction into the soil. The aim of this study was to evaluate the influence of Humistar (a concentrate of exogenous humic acids 12 % w/w and fulvic acids 3 % w/w; abbreviated: HU) applied with KI or KIO3 on the efficiency of iodine biofortification, yield and the accumulation of undesirable compounds in spinach
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