Study on Iodine and Bromine in Soil-Plant System in Relation to the “Reclamation-Akagare” Disease of Lowland Rice by Means of Radioisotope-Techniques

Abstract

In order to substantiate the hypothetical view that the iodine toxicity is responsible for the “Reclamation-Akagare” disease of lowland rice, a study on iodine and bromine in soil-plant system was performed by means of activation analysis and tracer technique.
The soils in volcanic ash origin from Kanto district contained 14 to 23 ppm I and 55 to 139 ppm Br, and the ratios of I/Br were from 0.12 to 0.41. According to an incubation test using an Akagare-soil of Nishinasu, the oxidative retention and reductive liberation of soil iodine was well recognized, and the maximum of 60 to 70% of soil iodine was released under submerged condition, resulting in about 4 ppm I in soil solution.
A plant culture test of rice revealed that the availabilities of iodine and bromine in soil as well as the applied ¹³¹I were highly variable due to soil conditions, such as moisture status, accompanied chloride and calcium addition. Among these treatments, soil submergence was most predominant for increasing their uptake by root, especially in iodine. In the case of Nishinasu soil, the contents in dried plant ranged from 1.3 to 341 ppm I and from 46 to 2170 ppm Br.