Abstract
Iodine deficiency disorders (IDD) in sub-Saharan African countries are related to low dietary I intake and generally combatted through salt iodisation. Agronomic biofortification of food crops may be an alternative approach. This study assessed the effectiveness of I biofortification of green vegetables (Brassica napus L and Amaranthus retroflexus L.) grown in tropical soils with contrasting chemistry and fertility. Application rates of 0, 5 and 10 kg ha−1I applied to foliage or soil were assessed. Leaves were harvested fortnightly for ~ 2 months after I application before a second crop was grown to assess the availability of residual soil I. A separate experiment was used to investigate storage of I within the plants. Iodine concentration and uptake in sequential harvests showed a sharp drop within 28 days of I application in all soil types for all I application levels and methods. This rapid decline likely reflects I fixation in the soil. Iodine biofortification increased I uptake and concentration in the vegetables to a level useful for increasing dietary I intake and could be a feasible way to reduce IDD in tropical regions. However, biofortification of green vegetables which are subject to multiple harvests requires repeated I applications.
Highlights
Iodine (I) is a constituent of thyroid hormones and critical for metabolism and overall human health (Ujowundu et al 2011)
Salt iodisation has been adopted with the aim of increasing dietary I intake to combat risks of Iodine deficiency disorders (IDD)
The sum of exchangeable cations, exchange capacity’ (ECEC), soil organic carbon (SOC) and nitrogen (N) contents were all greatest in the Vertisol and least in the Oxisol
Summary
Iodine (I) is a constituent of thyroid hormones and critical for metabolism and overall human health (Ujowundu et al 2011). Salt iodisation has been adopted with the aim of increasing dietary I intake to combat risks of IDD. In sub-Saharan countries such as Malawi, salt iodisation has been declared adequate to meet recommended dietary I intake (IGN 2017), salt intake varies according to cultural and economic factors (Joy et al 2015). Of I from foods other than salt is inadequate to meet the requirements of almost 100% of households in Malawi, and were this not present in the Malawian diet, there would be a typical dietary I intake of 12 lg day-1 (Joy et al 2015) and the same is true across much of the world
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