As is well-known, the iodine deficiency disorders (IDD) have tremendous adverse effects on the growth and development of human beings. The universal salt iodization (USI) has been introduced for the control and elimination of IDD in many countries. However, excessive iodine intake caused by USI may lead to new diseases such as hyperthyreosis, high level iodine goiter and thyroid cancer. Meanwhile, other investigations indicated that organic iodine is much safer than inorganic iodine added in salt.
A new strategy has been confirmed by pot and hydroponic experiments to cultivate the iodine- rich crops through biofortification for iodine supplement. This study aims to testify the feasibility of cultivating iodine-rich crops in a large scale under natural conditions, thus exploring a potential way for the prevention and elimination of the IDD.
Randomized block experiments were conducted in the farmland in Sha’an Village of Bihu Basin, which located in Lishui City of Zhejiang south mountain area, to explore the biofortification effect of seaweed iodine fertilizer on iodine contents of rice, vegetables and fruits in the field. The seaweed iodine fertilizer was prepared by mixing the smashed kelp with diatomite according to patent formula. The treatments of exogenous iodine were as follows：0, 0.375, 0.750, 1.500, 3.000, and 4.500 kg/hm². Spectrophotometric method was used to detect the iodine contents of crops and soil samples, and one-way analysis of variance was applied to analyze the difference of iodine contents among all treatments.
The results suggested that the iodine content in the edible parts of all the tested crops were significantly enhanced (P＜0.05) after biofortification by the seaweed iodine fertilizer, including rice, loofah, cucumber, tomato, eggplant, watermelon, edamame, cowpea, etc. The iodine content of rice grain on a dry mass basis increased from 0.019 mg/kg to 0.403 mg/kg after iodine biofortification, while the iodine content of the vegetables and fruits on a fresh mass basis may be enhanced from 0.01-0.05 mg/kg to 0.130 mg/kg after iodine application. Besides, the iodine translocation factors from the roots to the edible parts of cowpea and edamame were relatively higher than the others. A daily consumption of 0.38 kg fresh iodine-rich vegetables or fruits and 0.40 kg iodine-biofortified rice can offer 150 μg/d iodine for adults, which can meet the daily iodine intake recommended by the World Health Organization (WHO).
In conclusion, the iodine content varied significantly in different parts of rice, and increased gradually from roots to straws and grains. Low concentration (0.375 kg/hm²) of exogenous iodine had little effect on the iodine content of the edible parts of crops, while high concentration (≥3.000 kg/hm²) of exogenous iodine could reduce the iodine content of the edible parts of crops. Upon overall consideration of the costs and benefits for the plantation, 1.500 kg/hm² should be an optimal exogenous iodine dosage for the cultivation of iodine-rich crops in the field.