Soil versus foliar iodine fertilization as a biofortification strategy for field-grown vegetables

Abstract

Iodine (I) biofortification of vegetables by means of soil and foliar applications was investigated in field experiments on a sandy loam soil. Supply of iodine to the soil in trial plots fertilized with potassium iodide (KI) and potassium iodate directly before planting (0, 1.0, 2.5, 7.5, and 15 kg I ha-1) increased the iodine concentration in the edible plant parts. The highest iodine accumulation levels were observed in the first growing season: In butterhead lettuce and kohlrabi the desired iodine content [50–100 μg I (100 g FM)-1] was obtained or exceeded at a fertilizer rate of 7.5 kg IO3--I ha-1 without a significant yield reduction or impairment of the marketable quality. In contrast, supplying KI at the same rate resulted in a much lower iodine enrichment and clearly visible growth impairment. Soil applied iodine was phytoavailable only for a short period of time as indicated by a rapid decline of CaCl2-extractable iodine in the top soil. Consequently, long-term effects of a one-time iodine soil fertilization could not be observed. A comparison between the soil and the foliar fertilization revealed a better performance of iodine applied aerially to butterhead lettuce, which reached the desired iodine accumulation in edible plant parts at a fertilizer rate of 0.5 kg I--I ha-1. In contrast, the iodine content in the tuber of sprayed kohlrabi remained far below the targeted range. The results indicate that a sufficient spreading of iodine applied on the edible plant parts is crucial for the efficiency of the foliar approach and leafy vegetables are the more suitable target crops. The low iodine doses needed as well as the easy and inexpensive application may favor the implementation of foliar sprays as the preferred iodine biofortification strategy in practice.

Use of Iodine to Biofortify and Promote Growth and Stress Tolerance in Crops

“…This reductase activity also occurs in microorganisms (Amachi, 2008), but the magnitude of the microbial contribution in the soil process is unknown. In soils ${\text{IO}}_3^{-}$ is more efficient taken up by plants compared to I − (Lawson et al, 2015), and in soilless cultures the application of I − induces toxicity more easily in plants than does ${\text{IO}}_3^{-}$ (Borst Pauwels, 1962; Umaly and Poel, 1971; Muramatsu et al, 1983; Zhu et al, 2003). The lower toxicity of ${\text{IO}}_3^{-}$ could be explained by the iodate as an alternative substrate to other abundant enzymes, such as nitrate reductase (Barber and Notton, 1990), or by the activation of iodate reductase through ${\text{IO}}_3^{-}$ inducing other responses associated with redox signaling and iodine metabolism in plants, in addition to the reduction of ${\text{IO}}_3^{-}$.…”

Biofortificación con yodo en plantas para consumo humano

“…One way to avoid the complexity of the phenomena of absorption and transport of iodine when applied to the soil, is to apply it through foliar spraying as iodide and iodate (Zanirato and Mayerle, 2009), finding good results when compared to soil applications (Lawson et al, 2015). In another recent study Tonacchera et al (2013) achieved to increase iodine concentration in potato, carrot, tomato and lettuce applying iodine as foliar spray.…”

“…Una forma para evitar la complejidad de los fenómenos de absorción y transporte del yodo cuando este se aplica al suelo, es aplicarlo por medio de aspersión foliar en forma de yoduro y yodato (Zanirato y Mayerle, 2009), encontrándose buenos resultados al compararlo con las aplicaciones al suelo (Lawson et al, 2015). En otro estudio reciente Tonacchera et al (2013) lograron aumentar la concentración de yodo en papa, zanahoria, tomate y lechuga aplicando yodo como aspersión foliar.…”

Aplicaciones de aluminio mantienen el crecimiento de fresa (Fragaria × ananassa Duch.) suplementada con roca fosfórica en condiciones de cultivo sin suelo.

“…Lo anterior puede deberse a una toxicidad causada por el Al cuando este se aplicó directamente sobre las hojas, ya que estas no cuentan con mecanismos para excluir su absorción. Similares resultados se han reportado en lechuga (Lawson et al, 2015) y rábano (Strzelecki et al, 2010), en los cuales se compararon aplicaciones foliares y al suelo para aumentar los niveles de yodo; asimismo, el aumento en la cantidad de yodo se correlacionó con una disminución de la biomasa en rábano, pimiento y apio (Strzelecki et al, 2010).…”