Study On Transfer And Transform Of Iodine In Soil-Crop System

In humans and other animals, iodine (I) is essential to health and forms an important constituent of the thyroid hormones thyroxine (T4) and triiodothyronine (T3). These hormones play a fundamental biological role controlling growth and development. If the hormone production is reduced it will results in a group of conditions in man, referred to as Iodine Deficiency Disorders (IDD). IDD include cretinism, mental retardation, deafness and retarded growth. In order to control and even to eliminate the IDD, it is necessary to get a better understanding of the transfer and transform of iodine in soil-crop system. For the purpose an isotope tracer experiment was conducted to study ¹²⁵I dynamics in the soil and diffirenent exterior iodine fertilizers was introduced to study the transfer and transform of the exterior iodine. The results showed that ¹²⁵I introduced into the soil inclined with the soil depth, but most of the applied ¹²⁵I remained in the 0⁶cm from surface layer and lower of ¹²⁵I moved downwards and volatilized into the air. The outer iodized fertilizer which was added into the soil would be help to the ¹²⁵I transfer in the soil. The ¹²⁵I, adsorption in the soil and absorption in the plant, could released into the air. The extraction content of the inorganic iodine was very great in the soil with the deionied water, CaCl₂, and acetum solution and the extraction ratio would be more than 90% of inorganic iodine in the CaCl₂, and acetum solution, which indicated the outer iodine added into the soil would be utilized by the plant but also readily move with the water in the soil. In addition, the iodate ion could activate the background iodine in the soil and at the same time, it would be turn into iodine ion in acid soil. The acidity of the soil had some effect in the extraction of iodine, and the extraction content of iodine would be lowest at pH4.6 and it would increase at pH6.5. In the acidic soil the iodine existed as iodine ion, and in the neutral soil the iodine existed as iodate ion. When the iodine was added into the soil, the iodine content would be increased in the arable layer of the soil and the crop roots.